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The Neurological Exam

Thorough Small Animal Neurological Examination

The purpose of the neurological exam is to determine:

  1. Is there neurological disease?
  2. If so, is it in the brain, spinal cord or neuromuscular system?
  3. Be as precise as possible to determine the work up plan.

The neurological examination findings only tell us where the problem is but not what is causing it. Diagnostic testing will be needed to narrow down the diagnoses.

Because clinical signs are the same in two different dogs does not mean that they have the same diagnosis. Clinical signs reflect localization.  For example, if you lined up 3 dogs, one with a brain tumor, one that had a stroke and one that had a focal area of inflammation in the same area of the brain, their clinical signs would be similar, to identical.

Thus, the neurological exam tells us the location of disease and allows us to focus our diagnostic testing to a specific area of the nervous system.

The neurological examination is divided in five components of testing

  1. Mental awareness, gait and posture
  2. Cranial nerve examination
  3. Proprioception and placing
  4. Appendicular reflexes
  5. Pain evaluation and symmetry

 

PART I: MENTATION, GAIT AND POSTURE

Mental Status

Here we assess the animal’s level of consciousness, or mentation.  Knowledge of the patient’s mental status informs the examiner of the likelihood that damage has occurred to either the cerebral cortex and/or the ascending reticular activating system (ARAS). Thorough conversation with the owner will allow the examiner to know the “normal” from the abnormal for that patient.

How is the test done:

Quiet observation of the patient in a spacious room with a few obstacles while taking a history. Note if the patient is disoriented, gets stuck in corners, prefers to pace, seems to respond to the environment normally for that species and breed and per the owner’s feedback of the personality of the patient.

What do results mean:

Normal consciousness requires a functional cerebral cortex appropriately stimulated by activity within the ascending reticular activating system.  To describe the mentation, the terms alert, obtunded (dull), delirious (demented, disoriented), stuporous, semi-comatose or comatose are used.  Vocalization is part of the findings one looks for.

 

Behavior

Assess if the patient is showing behavioral changes that may impact the findings from the remainder of the neurologic examination.

How is the test done:

Many of the behavior changes will be reported in the history by the owner and include clinical

signs associated with behavioral abnormalities such as: lethargy, depression, obtundation, stupor, delirium, failure to learn, circling, pacing, polydipsia, polyphagia, pica, anorexia, and destructive behaviors.

What do results mean:

Normal behavior is the result of the entire nervous system action.  Because behavior is primarily controlled by the forebrain, changes can result from structural, psychologic, or metabolic abnormalities within the telencephalon or diencephalon.  Structural abnormalities, such as neoplasia, inflammation, or degeneration, may lead to behavioral changes if some component of the limbic system is involved in the structural abnormality. Behavioral changes can also be due to psychologic disturbances with structural and metabolic abnormalities excluded, or may be from metabolic disturbances, such as might occur with abnormal neurotransmitter levels or interactions.  Understand that because so much of the nervous system is involved in behavior, it can be challenging to localize a lesion just based on this.

 

Posture and gait

Careful examination and observation of the gait will help the examiner determine if any lameness is noted and if it is more orthopedic or neurological. As well, balance and dysmetria can be assessed

How do you test for:

Begin observation in the waiting room and observe while patient is walked to the spacious exam room. Ensure non-slip surfaces for easy of traction. If the clinic is small, the outdoor sidewalk will come handy. Note how the patient moves limbs, head and neck as well as tail. How the patient sits, stands, walks, trots will be informative. Walking in tight circles, up and down curves also can exaggerate signs. Observe circumduction, abduction, adduction and interference during gaiting

During the evaluation, make note of how the animal rises from a sitting position, how it sits from a standing position, and how the animal positions its limbs when standing and walking.  Most neurologic deficits related to posture and gait are exacerbated by turning or tight circling.  Therefore, the examiner should routinely assess these movements to avoid overlooking subtle deficits for which the animal can otherwise compensate during unidirectional travel. Use the time to take a history to observe the patient in a non-stressful manner, off leash.

What do findings mean:

There exists a grading system to assess the posture and gait caused by spinal cord lesions between segments T3 and L3. Paresis means weakness and the patient can be ambulatory or non-ambulatory. Paralysis is also called -plegia and is used when motor function no longer exists. Dysmetria is a poor judgement of distance and can be hypo- (not enough) or hyper- (too much) distance gauging. Ataxia is a loss of balance. Ataxia has nothing to do with weakness. The term para- means back limbs whereas if thoracic limbs only are affected there is no special term. Quadra- or tetra- reflects all four limbs affected.

 

PART II: CRANIAL NERVE EXAMINATION

CN I – Olfactory

Remember that olfaction requires cortical awareness which probably labels this test as more of a reaction than a reflex. This function is sensory.

How do you test for:

There are two ways to do this test. One is to cover the animal’s eyes using your hands or a blindfold to prevent visual input.  Then place a pleasurable or offensive odorant in front of the external nares and watch for a behavioral response. Another option is to hide a very tasty treat in one hand and both hands closed in front of the patient. Dogs are very likely to find the treat. Cats can ignore it all. Make sure the treat only has been in one hand or the patient can identify the scent in the hand without the treat and the test can be non-relevant.

What do findings mean:  

The animal should react to a pleasant odor and follow the source as it is moved in front of the external nares.  However, an offensive odor will result in avoidance behaviors such as turning the head away from the source. Few clients complain of anosmia in their pet but clinicians must consider it as a possibly cause of loss of appetite.  The most common cause of such deficiencies is severe rhinitis, but tumors within the nasal passages or those involving the cribriform plate are also deserving of consideration.  Viral infections (e.g. canine distemper virus, parainfluenza virus) and other inflammatory diseases can also impair the olfactory system.

CN II – Optic

Tracking

Visual tracking is a reaction rather than a reflex. It requires cortical awareness and the generation of a behavioral response. It involves the midbrain, particularly the rostral colliculi.

How do you test for:

The examiner can gather a general assessment of vision by observing the animal as it moves around the exam room and navigates around obstacles.  Visual tracking is then assessed by standing behind or above the animal, in a place the animal cannot see the examiner’s hands. Cotton balls are the best tool as they are non-odorant and do not make noise when landing thus not stimulating smell and hearing. Toss the cotton balls about in a direction about 45 degrees from the midline in front of the eye. The patient’s response is an eye or whole head movement towards the cotton ball as it lands. Assess both sides a couple of times.  

What do findings mean:

The animal should follow the fall of objects through each visual field.  Damage to the retina, optic nerve, optic chiasm, or optic tract will not only impair vision, but will also cause deficits in the pupillary light reflexes.  Damage to the cranial colliculus, lateral geniculate nucleus, optic radiation, or occipital cortex will produce visual deficits alone.

Menace

Menace evaluates the integrity of the visual system (sensory pathway) and the facial nerve (motor pathway). As well the globe will pull back as a response (abducens nerve).  Since it requires cortical awareness, this test produces a reaction rather than a reflex. Menace as a learned response is coordinated by the cerebellum.

How do you test for:

The stimulus is threatening gesture with finger, hand or object in front of the eyes, one at a time. The response is blinking of the eye (VII) and pulling the globe back (VI).  Avoid touching the skin, hair, or vibrissae of the face and gestures that produce air currents when performing the menace test as this will stimulate trigeminal afferents.

What do findings mean:

The normal response to a menacing gesture is a blink that can sometimes be accompanied by aversive movement of the head.  Normal cats will occasionally fail to menace despite having intact vision and facial nerve function.  Since the menace reaction is a learned response, it may be absent in very young animals under 8-12 weeks.  Failure to blink may be due to paralysis of the m. orbicularis oculi (facial n.) or may indicate blindness (retina, optic n., optic chiasm, optic tracts, lateral geniculate nucleus, optic radiation, occipital cortex).  To differentiate between these possibilities, observe the animal in unfamiliar surroundings to see if it avoids and navigates around obstacles.  Other tests that provide a good assessment of vision include the visual placing reaction and visual tracking of a moving object.  An animal with facial nerve paresis or paralysis may withdraw its head in an avoidance reaction or may retract the globe protrude the third eyelid briefly in response to a menacing gesture. The menace reaction involves a rather complex pathway and is often absent when extensive cerebellar disease is present.

Visual Placing

This test evaluates the patient’s ability to locate an obstacle visually and place on that obstacle as it approaches. Not only is vision evaluated but the interpretation and response as well thus needing complex pathways through forebrain and midbrain.

How do you test for:

Hold the animal so that the thoracic limb to be tested is farthest from the examiner’s body.  Cover the eye on the same side as the non-tested limb; the eye that is ipsilateral to the tested thoracic limb should not be covered.  Then move the animal toward a flat surface, such as an exam table, so that the limb distal to the carpus comes near with the table’s edge.  The procedure is repeated for the contralateral thoracic limb but only after the examiner has repositioned the animal and covered the appropriate eye. This test is done on the thoracic limbs only and is only done on smaller animals due to weight.

What do findings mean:

A normal animal will lift the tested limb and reach for the approaching table before the dorsum of the paw contacts the table’s edge.  Following this effort, the animal should place the limb in an appropriate weight-bearing position upon the surface of the table. Patients used to be held may not respond and thus need to be placed in a less secure position away from the examiner’s body.  Weakness, asymmetry, or absence of an effort to reach forward with the limb and place it normally on the table surface usually indicates dysfunction somewhere along the sensory or motor pathways responsible for this reaction.  Findings from the remainder of the neurologic exam will help differentiate among these possibilities to further localize the site of damage.

Pupillary Light Reflex

The pupillary light reflex (PLR) allows the examiner to assess the integrity of the optic nerve (CN II) pathway that serves as the afferent limb and the parasympathetic component of the oculomotor nerve (CN III) that provides the efferent limb.

How do you test for:

The examiner should first compare the size of the resting pupils from a distance and make note of any asymmetry, known as anisocoria.  Then use a bright light source and shine it into the pupil of one eye.  The light should be close to the eye but not touching it.  Observe the direct response of the eye into which you are shining the light and the indirect (consensual) response of the opposite eye.  Repeat this procedure for the other eye.

What do findings mean:

Directing the strong light source into one eye should elicit rapid constriction of the pupil (direct pupillary light reflex).  The contralateral pupil should also constrict, although the degree of constriction may be less than that of the eye into which the light is directed (indirect, consensual pupillary light reflex).  Lesions that affect the retina, optic nerve, optic chiasm, or optic tract will produce visual and pupillary deficits.  Lesions affecting the pretectal nuclei, the parasympathetic nucleus of the oculomotor nerve, the oculomotor nerve, the ciliary ganglion, the short ciliary nerves, or the m. constrictor papillae will produce pupillary deficits without affecting vision.  Therefore, pupillary light reflexes can be normal with total cortical blindness.  They can also be normal in the face of retinal disease that renders a patient effectively blind because the number of functional retinal cells necessary to generate the PLR is very small.  Severe damage to the retina or optic nerve will cause pupillary dilation (mydriasis) on the affected side and failure of both the direct and indirect pupillary light reflexes.  However, the pupil will react to light shined in the contralateral eye (indirect PLR).  Vision will be impaired or absent in the affected eye.

Cranial Nerve III – Oculomotor

Movement and Position

This test evaluates the functional integrity of the oculomotor (CN III), trochlear (CN IV), and abducent (CN VI) nerves which are responsible for producing conjugate movement of both eyes in the same direction at the same time.

How do you test for:

Turn the head from side to side or up and down while watching the eyes.  It may help to hold the eyelids open while performing this test.  Watch the globes move and catch up towards the side of the movement after a slight delay to the opposite side. When done moving the head also check for spontaneous nystagmus which will give indication of vestibular disease if noted.

What do findings mean:

The eyes should move freely and conjugately in all directions and should be centered in the palpebral fissures when at rest.  Side to side head movements should elicit horizontal physiologic nystagmus with obvious laterad (abducent nerve) and mediad (oculomotor nerve) eye movements.  Likewise, movement of the head in the vertical plane should elicit vertical physiologic nystagmus (oculomotor nerve).  Paresis or paralysis of the extraocular muscles due to lesions of the oculomotor, trochlear, or abducent nerves results in fixation of the globe, disconjugate eye movements, and failure to exhibit a full range of ocular motion.  As well as changes in movement, note that lesions of the oculomotor nerve will produce a ventrolateral strabismus of the affected eye and a decrease or absence of medial movement during elicited physiologic nystagmus and lesions of the trochlear nerve may produce rotation of the globe but this is difficult to appreciate in species with round pupils without a fundic exam.  Lesions of the abducent nerve will produce a medial strabismus.

Pupillary Light Reflex

See above

Cranial Nerve IV – Trochlear

Movement and Position

See above

Cranial Nerve V – Trigeminal

Jaw tone and symmetry of muscles of mastication

To evaluate the mandibular branch of the trigeminal nerve (CN Viii) and its motor innervation of the masticatory musculature.

How do you test for:

Palpation is key (mm. temporalis, masseter, pterygoideus, mylohyoideus, and the rostral belly of the m. digastricus) to compare their mass and tone for bilateral symmetry.  Then evaluate jaw tone by gently opening the mouth while assessing the amount of resistance with which this motion is met.  

What do findings mean:

Symmetry of the muscle mass and normal prehension and drinking should be present. When resting, the jaw should not be dropped but unilateral damage does not usually interfere with jaw closure, but may result in decreased jaw tone or slight deviation of the jaw toward the normal side due to unopposed tone in the normal pterygoid muscles.  Chewing may also be asymmetric.  Trismus, also known as 'lockjaw', is prolonged spasm of the muscles of mastication as seen in tetanus.  Lesions in the medulla that involve the spinal tract of the trigeminal nerve will cause ipsilateral loss of facial sensation but motor innervation to the masticatory muscles will be unaffected.  Lesions in the pons or those that affect both sensory and motor nerve fibers will cause loss of both sensory and motor function.  Lesions in the trigeminal motor nucleus or those that preferentially affect motor fibers will cause selective loss of motor function with no sensory impairment.

Palpebral reflex

The reflex arcs that exist between both the ophthalmic (CN Vi) and maxillary (CN Vii) branches of  the trigeminal nerve and the facial nerve (CN VII) are evaluated

How do you test for:

A hemostat or fingertip is used to lightly touch the medial, and then lateral, canthus of the eye and the result is a blink response.  The examiner can then use the hemostat to apply a light stimulus to the mucosa of the nasal vestibule.  This stimulus will not only elicit the brainstem-mediated palpebral reflex, but should also elicit an avoidance reaction that requires central integration and cortical awareness.

What do findings mean:

Touching the medial and lateral canthi should elicit the palpebral reflex and the animal should completely close the eyelids, or blink.  Animals that are naturally exophthalmic (Pekingese, Pugs, etc.) may incompletely close the eyelids.  In these cases, preexisting evidence of exophthalmia is generally evident and may include corneal pigmentation and scarring secondary to exposure irritation.  A lesion that affects the trigeminal nerve, brainstem integration pathway, or facial nerve will reduce or eliminate the palpebral reflex.  Touching the mucosa of the nasal vestibule should elicit both the palpebral reflex and an avoidance reaction, or movement of the head away from the stimulus.  The pathway involved in this reaction requires transmission of afferent information along the ophthalmic branch of the trigeminal nerve, relay through the thalamus, and conscious integration in the somesthetic cortex.  Upper motor neurons in the somesthetic cortex activate multiple somatic nerves to generate the voluntary avoidance movement.  A lesion anywhere along this pathway will reduce or eliminate this reaction.

 Corneal Reflex

This test evaluates the reflex arc that exists between the ophthalmic (CN Vi) branch of the trigeminal nerve and the abducent nerve (CN VI).

How do you test for:

Holding the eyelids open, briefly (and gently) touch the cornea using a moistened cotton tip applicator.  Retraction of the globe and protrusion of the third eyelid should easily be visualized if the eyelids are held open throughout the test.  

What do findings mean:

Stimulation of the cornea (CN Vi) should cause reflex retraction of the globe (CN VI) and passive protrusion of the third eyelid.  Damage to the sensory limb of the corneal reflex may produce decreased or absent corneal sensitivity without affecting innervation to the mm. retractor bulbi by the abducent nerve.  Similarly, damage to the motor limb of the corneal reflex can result in selective loss of innervation to the mm. retractor bulbi without affecting corneal sensitivity.  Therefore, a lesion that affects the ophthalmic branch of the trigeminal nerve, brainstem integration pathways, or the abducent nerve will reduce or eliminate the corneal reflex.

Autonomous zones

This evaluates the sensory distribution of the ophthalmic (CN Vi), maxillary (CN Vii), and mandibular (CN Viii) branches of the trigeminal nerve.

How do you test for:

The examiner should use the tip of a hemostat to gently touch the medial aspect of the nasal vestibule to assess the cutaneous autonomous zone of the ophthalmic nerve.  Care must be taken to avoid stimulating the planum nasale as this will activate the infraorbital nerve, a direct continuation of the maxillary nerve.  Gently pinch the upper lip with a hemostat or nails to assess the cutaneous autonomous zone of the maxillary nerve.  A similar stimulus should be applied to the lower lip to assess the cutaneous autonomous zone of the mandibular nerve.  The animal should respond to each of these stimuli by generating avoidance behavior that generally includes withdrawal of the head from the inciting stimulus.

What do findings mean:

A lesion that affects the ophthalmic, maxillary, or mandibular nerve will reduce or eliminate the reaction to a noxious stimulus applied to its respective autonomous zone.  Damage to the ipsilateral brainstem, thalamus, or contralateral cerebral cortex can produce unilateral elimination of the animal’s reaction to a noxious stimulus.

Cranial Nerve VI – Abducens

Movement and Position

See above

Cranial Nerve VII – Facial

Facial expression

This helps evaluate the motor component of the facial nerve (CN VII).

How do you test for:

Compare left and right side of the face for symmetry by evaluating the eyelids, palpebral fissures, lips, and ears.  Watch the nostrils as the animal breathes to determine whether they are both flaring on inhalation.  Observe spontaneous blinking and ear movements.  Note any asymmetry in the corner of the lips as the head and neck are extended.  After passively observing the animal, the examiner should then apply a noxious stimulus to each of the cutaneous autonomous zones of the trigeminal nerve while noting the animal’s reaction.

What do findings mean:

The normal animal will have symmetrical muscles of facial expression.  Spontaneous blinking and ear movements will also be readily observable.  The animal should respond to noxious stimulation of trigeminal afferents by generating avoidance behavior that may include withdrawal of the head, curling the lip, or even biting.  Unilateral lesions lead to asymmetry. Initially the side affected is droopier and over time seems even then later may show contraction. In the case of the nares, deviation may occur.  Since facial expression requires cortical involvement, lesions that affect upper motor neurons to the facial motor nucleus may cause abnormal facial expression without affecting palpebral reflexes.  It has also been shown that diseases of the inner ear may extend to the facial nerve to produce ipsilateral facial paralysis.

Taste

The goal is to evaluate the chorda tympani, a branch of the facial nerve that supplies gustatory fibers to the rostral two-thirds of the tongue.

How do you test for:

Use a cotton-tipped applicator to apply a bitter tastant (atropine or tartaric acid) to the rostral two-thirds of the tongue. The best place is between upper and lower teeth, laterally when lifting lips.  If facial nerve damage is suspected, it is recommended that the examiner test gustation on the affected side of the tongue first and watching for a reaction or lack thereof.  The contralateral half of the tongue can then be assessed. The response is moving head away or licking or hypersalivation. Count licks number.

What do findings mean:  

Immediate salivation is a result of reflex activity between special visceral afferent fibers of the chorda tympani and the parasympathetic nuclei of cranial nerves VII, IX, and X that innervate the salivary glands.  The animal will react to the stimulus with chewing motions, extension of the tongue, and head shaking to eliminate the bitter taste from its mouth.  This reaction requires conscious perception and voluntary activation of general somatic efferent neurons in the hypoglossal nucleus and the motor nucleus of the facial nerve.  Facial nerve damage involving the chorda tympani will decrease or eliminate the animal’s reaction to a bitter tastant.  With repeated application of a tastant, the animal will learn to anticipate the stimulus and react accordingly.  Since this can interfere with your evaluation, it is recommended that the examiner begin by testing the affected side before proceeding to test the normally innervated side of the tongue.

Facial Tear production- STT

Lacrimal glands are innervated by the parasympathetic of CN VII. STT paper provides a noxious stimulation of the cornea and conjunctiva and tears result via a reflex arc between ophthalmic (CN Vi) afferent fibers and general visceral efferent fibers of the facial nerve (CN VII).

How do you test for:

The Schirmer tear test is a means of evaluating production of the precorneal tear film.  This test utilizes a sterile strip of absorbent paper that is standardized to absorb aqueous solutions at a constant rate.  The examiner inserts the notched end of the strip into the conjunctival sac and holds the palpebrae shut for 60 seconds.  After 60 seconds, the strip is removed and the amount of moisture is measured.  This procedure is repeated for the opposite eye and the findings are compared.  It is important to remember that the minor irritation caused by the strip is necessary to performance of the test so the Schirmer tear test cannot be performed after application of topical anesthetics.  Normal and abnormal reference values are available for several species.  

What do findings mean:

Inadequate tear production may suggest loss of parasympathetic innervation to the lacrimal gland.  This could result with damage to the major petrosal nerve since it carries the preganglionic parasympathetic fibers that synapse in the pterygopalatine ganglion.  Similar results would be produced by damaging the lacrimal nerve since it carries the postganglionic parasympathetic fibers that arise in the pterygopalatine ganglion.  Another condition that will cause inadequate tearing is keratoconjunctivitis sicca (KCS), or ‘dry eye’.  In contrast, blockage of the nasolacrimal duct will produce epiphora, or overflow of tears onto the face, due to inadequate drainage of the precorneal tear film.  

Cranial Nerve VIII- Vestibulocochlear

Hearing

Evaluate the cochlear division of the vestibulocochlear nerve (CN VIII).

How do you test for:

Snapping fingers is rather unspecific to test hearing. The animal will turn head towards the sound as a response. The most specific way to assess audition is via electrophysiologic tests known as Brainstem Auditory Evoked Potentials (BAEP) that allow the examiner to localize which side is affected in cases of unilateral deafness.  Since these are not very practical in a general practice setting, it is more common to perform a rather crude evaluation of audition.

What do findings mean:

Deafness can be classified as either sensorineural, conductive or central in nature.  Subtotal hearing loss is extremely difficult to detect/quantify.  Damage to the external or middle ear will result in conductive deafness, whereas inner ear lesions will cause sensorineural deafness.  Conductive deafness is most often caused by chronic otitis externa or media.  It usually only causes partial hearing loss.  In sensorineural deafness, the specialized receptor cells either fail to develop or are damaged by toxins (e.g., aminoglycosides, chloramphenicol, furosemide, etc.).  Damage to these receptors or the cochlear nerve itself will result in complete deafness. Central deafness refers to lesion that are affecting hearing pathway intracranially.

Gait and Stance

Initial way to evaluate the vestibular division of the vestibulocochlear nerve (CN VIII).

How do you test for:

Observe from all sides and during gait, circles to both sides and blindfolded if needed because patients with vestibular ataxia use vision to compensate and maintain their balance.  

What do findings mean:  

The normal animal will have a straight body axis with a regular and purposeful gait.  The animal may lean, drift, fall, circle, or even roll toward the affected side.  Torticollis may be evident with the concave surface of the body on the same side as the vestibular lesion.  Occasionally, there will be mild hypertonia in the limbs that are contralateral to the side of damage.  Interestingly, cats will often carry their tails straight up when they experience significant loss of balance. The lesion is usually ipsilateral to the side of lean, head tilt, circling.

 Nystagmus/strabismus

 How do you test for:

Begin by noting any abnormal deviation of the eyes, strabismus (failure to maintain the eyes in a conjugate visual axis), resting nystagmus, or lack of movement in a certain direction.  Elicit normal physiologic nystagmus by gently directing the patient’s head from side to side and then up and down.  The animal should display normal, conjugate nystagmus in the direction of head movement.  Sequentially place the animal in right lateral, dorsal, and left lateral recumbency while observing the eyes at each position for signs of positional nystagmus.  A normal patient will have no evidence of positional nystagmus.

What do findings mean:

The fast phase away from the affected side, and head tilt and circling toward the side of the lesion.  Strabismus may be present.  Unlike strabismus due to paralysis of extraocular eye muscles, vestibular strabismus is usually positional.  The usual presentation is a ventral or ventrolateral deviation of the eye ipsilateral to the lesion when the nose is elevated.  Be aware that this eye movement is normal in horses and cattle.  Peripheral (inner ear) and central (brainstem) lesions can be differentiated based on the following clinical features:

  1. Peripheral lesions will not affect ascending or descending tracts that are not specifically part of the vestibular system.  Therefore, the patient will have normal proprioception and normal strength.  Paresis and loss of general proprioception may indicate a brainstem lesion.
  2. The thought that vertical nystagmus is always central is not always so. But a Disconjugate nystagmus is.

Cranial Nerve IX – glossopharyngeal

Taste

The glossopharyngeal nerve (CN IX) oversees taste and sensory distribution to the caudal one-third of the tongue.

How do you test for:

You can use the same method as for CN VII but it is harder to reach the caudal third of the tongue.

What do findings mean:

A better test is the gag reflex

Swallowing Reflex

How do you test for:

The most reliable means of assessing the animal’s ability to normally swallow is to provide the animal with food or water and observe as it eats and drinks. If you may plan a work up it may not be possible to feed the patient.  It is important to differentiate problems with swallowing from those with prehension or mastication.  Animals that are unable to prehend food due to paralysis of the muscles of mastication and/or the tongue may still swallow normally if a food bolus is delivered to the pharynx.  If the animal is too nervous to eat in the exam room, the owner’s description of the patient’s eating habits at home may become especially helpful.

What do findings mean:

The normal animal will prehend and swallow without difficulty.  Any abnormality or difficulty associated with swallowing is termed dysphagia.  Lesions that affect the rostral portion of the nucleus ambiguus (where the glossopharyngeal and vagus nerves originate), the general somatic efferent (GSE) axons in the glossopharyngeal or vagus nerves, or the muscles of the pharynx and esophagus will often produce dysphagia as the primary clinical sign.  The site and severity of the lesion will determine the severity of dysphagia displayed by the patient.  In the case of unilateral pharyngeal paresis, the animal retains some ability to swallow but is more likely to choke.  Bilateral paresis usually precludes swallowing and increases the likelihood of choking.  In these cases, it is also very common for patients to present with a depressed or absent gag reflex.  In both conditions, a major concern is the risk for aspiration of ingesta.

 Lesions that affect the glossopharyngeal nerve will also decrease or eliminate the animal’s reaction to a bitter tastant applied to the caudal one-third of the tongue.

Gag Reflex

How do you test for:

Use a finger down the throat to touch the base of the animal’s tongue or caudal wall of the pharynx.  Evaluate the subsequent gag reflex and ability of the animal to swallow normally. It is also helpful to evaluate the tongue for symmetry and coordinated movement now.  Exercise caution when testing the gag reflex in animals with questionable vaccine histories since rabies exposure is possible.  A less consistent, but safer way of inducing the gag reflex in aggressive animals or those suspected of having a zoonotic disease, is to apply pressure to the laryngeal/pharyngeal region externally.  However, this technique will not consistently elicit the gag reflex.  

What do findings mean:

The normal gag reflex consists of a brisk elevation of the soft palate and bilateral contraction of the pharyngeal muscles elicited by a stimulus in the caudal pharynx.  Avoid touching the soft palate when evaluating the glossopharyngeal nerve since this will elicit a similar reflex but the sensory limb will be the maxillary branch of the trigeminal nerve rather than the glossopharyngeal nerve.  The normal gag reflex is usually followed by swallowing.  

Cranial nerve X – Vagus

Gag/Swallow

See above

Cranial Nerve XI – Accessory

To evaluate the functional integrity of the accessory nerve. This test is not used much in small animal but more relevant in horses.

How do you test for:

Carefully palpate the neck to evaluate the symmetry, tone, and muscle mass of the trapezius, cleidomastoideus, cleidocephalicus, sternocephalicus, and omotransversarius muscles.  Be sure to make note of any atrophy or asymmetry.  Next gently flex the head and neck from side to side and then up and down to determine whether the animal adequately resists passive flexion.  Be sure to make note of either increased or decreased resistance to passive flexion in any direction.

What do findings mean:

Damage to the accessory nerve will produce ipsilateral atrophy of the trapezius, cleidomastoideus, cleidocephalicus, sternocephalicus, and omotransversarius muscles.  If palpable atrophy is not observed, the examiner may notice decreased resistance to passive flexion of the head and neck in the direction opposite the side of damage.  In chronic cases, the neck may deviate toward the affected side.  Lesions that affect the caudal portion of the nucleus ambiguus (where the accessory nerve originates), the general somatic efferent (GSE) axons in the internal branch of the accessory nerve, the cervical portion of the vagus nerve, the recurrent laryngeal nerve, or the caudal laryngeal nerve will often produce laryngeal paralysis.  Clinical signs of this condition include inspiratory dyspnea or stridor due to failure of the cricoarytenoideus dorsalis muscles to completely abduct the vocal folds.  In small animals, laryngeal paralysis is usually bilateral, but it is often unilateral in racehorses and is a common cause of poor performance.  Since the inspiratory dyspnea is usually of sufficient severity to be audible, horses with this condition are often referred to as "roarers."

Cranial Nerve XII – Hypoglossal

Tongue motor

How do you test for:

Water on the nostrils, observing after a gag will encourage the patient to lick and the function of the tongue can be observed. When doing the gag reflex, pay attention to the symmetry of the tongue.

What do findings mean:

Lesions that affect the hypoglossal nerve will impair normal functions of the tongue, including prehension, mastication, and deglutition.  Unilateral tongue atrophy is a reliable clinical sign of unilateral hypoglossal nerve damage.  Acute lesions will cause the tongue to deviate toward the denervated side on protrusion and toward the normal side on retraction due to unopposed contraction and then relaxation of the normal contralateral genioglossus and intrinsic tongue muscles.  With chronic lesions, however, it is common for the tongue to always deviate toward the denervated side due to atrophy and contracture of the paralyzed muscles rather than because of contraction of the normal contralateral muscles.

PART III: PROPRIOCEPTION

Proprioceptive Placing

All animal need to be able to recognize the spatial orientation and generate an adequate voluntary movement to place their limbs to a normal weight-bearing position.

How do you test for:

Straddle the patient over his chest area, facing forward and bend your knees slightly. With a lean over and reach to the sternum, one hand to provide support. The animal is not lifted but provided with support to avoid loss of balance when one leg is taken off the ground. The other hand slides slowly down the leg to the carpus and bends the leg back placing the dorsum of the paw on the ground. When the paw is released, normal CP is noted when the animal rights the paw back to normal supporting position immediately. The test is repeated two to three times for each front leg to ensure consistency. If the patient pulls the leg up, it is a withdrawal reflex and not a proprioceptive response.

For the back legs, the examiner is crouched behind the patient with one knee down. The ipsilateral hand to the up knee is placed under the pelvis and that same side elbow on the up knee to providing back support to the examiner, particularly for large and giant breed handling. The other hand slides down to the dorsum of the paw contralateral to the hand used to support and turned under. The righting response should be prompt. The test is repeated 2-3 times on each limb.

What do findings mean:

Proprioceptive placing is considered normal if the animal quickly recognizes the abnormal paw placement and generates an adequate voluntary movement to return the limb to an appropriate weight-bearing position.  Delayed or absent response means neurological deficits and not orthopedic. The cause of the delay is either perception deficit or initiation of movement malfunction.  However, animals that are generally weak for other disorders such as anemia, early shock, may not respond. The examiner must interpret the patient’s overall status to interpret proprioception.

Hopping

Evaluate all components required for voluntary limb movement, including proprioception, mechanoreception, muscle strength, weight bearing capacity, coordination, and balance.  Each limb is tested individually and thus, the hopping reaction is more sensitive and will assess more subtle abnormalities than other postural reactions.

How do you test for:

Straddling the animal over mid body, the examiner used legs to keep pelvic limbs in place. One hand reaches for the elbow and foreleg on one side and lifts that leg off the ground. Then the animal is pushed to the opposite side. The quality and speed of the hop is assessed. The animal is not lifted. Both sides are tested. The pelvic limbs can be also assessed but are not usually done

What do findings mean:

The hopping reaction is considered normal if the animal detects changes in its center of gravity upon lateral displacement and repositions the limb into its next weight-bearing position.  Hopping motions should be smooth, brisk, and regular.  The animal should show good strength and the limb should not collapse upon bearing weight.  Delay or failure to initiate the hopping reaction implies proprioceptive deficits involving interruption of sensory pathways while poor completion of hopping suggests paresis due to damage along the motor pathways.  This test is excellent in cats but some prefer to roll.

Wheelbarrowing

How do you test for:

Starting behind the animal, lift the back legs off the ground and push the animal forward as a wheelbarrow. Similar testing can be done by holding the front legs and pushing animal back. Head position should be neutral. Elevating the head will stimulate more vestibular pathways.

What do findings mean:

The normal animal will walk forward (thoracic limbs) or backward (pelvic limbs) in a coordinated manner so that weight is borne equally by both limbs. With head elevation, the response produces increased extensor tone in the forelimbs.  This is manifest clinically by a stiff and short-strided thoracic limb gait. Abnormalities include toe-scuffing or consistent lagging of one limb behind the other.  In cats, it is common to use wheelbarrowing as an alternative postural reaction to hopping since they respond more consistently to wheelbarrowing.  

Hemistanding & Hemiwalking

How do you test for:

Stand on the side of the animal contralateral to the limbs being evaluated.  Simultaneously lift both the thoracic and pelvic limbs closest to you off the ground by flexing and holding the carpus and tarsus, respectively. The animal needs to be kept body level.  Alternatively, the animal may be less resistant if more proximal joints (e.g. elbow, shoulder, stifle, hip) are flexed and held instead of the carpus and tarsus.  Allow the animal to regain its posture and balance after lifting the non-tested limbs (hemistand).  Then gently push the animal laterad away from its center of gravity to evaluate its ability to sequentially reposition the limbs and bear weight (hemiwalk).

What do findings mean:

A normal animal will maintain its posture and balance while hemistanding.  While hemiwalking, the animal should sequentially step with the ipsilateral thoracic and pelvic limbs in a controlled fashion while maintaining normal posture and balance.  The animal should place each limb in a normal weight-bearing position and should not collapse into the limb after stepping.  Likewise, the animal should initiate a voluntary movement to reposition the limbs before the torso becomes tilted too far over the center of gravity.  It is considered abnormal for the animal to hop with the ipsilateral thoracic and pelvic limbs simultaneously rather than in sequence.  Likewise, the sequential stepping efforts should be symmetrical between contralateral paired limbs.  

Extensor Postural Thrust

How do you test for:

Hug the animal from behind and around the chest, behind the front legs, then left it up with the legs off the ground. Gently bring the back limbs down to the ground again. The animal will place it limbs rapidly under itself with increased extensor tone and resume normal pelvic posture.

What do findings mean:

When lowered to the ground, a normal animal will extend the approaching limbs in anticipation of bearing weight.  Many animals (especially cats) will even hyperextend the digits of the tested limbs during the lowering phase of this reaction. The response is vestibular and thus when the vestibular system is affected, this response may or not be present. Any asymmetry in placing limbs is noted as abnormal.

Visual Placing Reaction

See above

Tactile Placing Reaction

To evaluate the animal’s ability to perceive and appropriately respond to the tactile stimulation provided by touching the dorsum of each distal thoracic limb to a table’s edge.

This test is done exactly like visual placing is done but both eyes are blindfolded in the process.

Righting Reaction

Evaluate the animal’s ability to right itself into a sternal position after being placed in lateral recumbency.

How do you test for:

The patient is placed in lateral and dorsal recumbency and once you let go, the animal should naturally right itself back sternal or standing

What do findings mean:

The righting response involves flexing all four limbs under the body and lifting the head and neck upwards into a more horizontal position.  Patients with abnormalities of the vestibular system, cerebellum, or any of the sensory and/or motor pathways necessary for normal postural reactions can show problems righting themselves from lateral to sternal recumbency.  Their attempts at righting may be delayed, uncoordinated, or altogether absent.

Tonic Neck Reaction

Another evaluation of the vestibular system and motor pathways that produce vestibulocervical responses following tonic neck movements assessing cerebellar modulation of neck, body, and limb posture with changes in head and neck position.

How do you test for –

Gently manipulate the neck up and then down to the sternum. Feel for resistance.

What do findings mean -  

The normal response is slight extension of the thoracic limbs and slight flexion of the pelvic limbs with extension of the neck and slight flexion of the thoracic limbs and slight extension of the pelvic limbs with flexion of the neck.  Lateral movement of the head and neck to one side should elicit slight extension of the ipsilateral thoracic limb and slight flexion of the contralateral thoracic limb. Normal animals may consciously inhibit the tonic neck reactions, but abnormalities will likely be seen in animals with proprioceptive or motor pathway deficits.  Cerebellar lesions will result in exaggerated tonic neck reactions.

PART IV: SPINAL REFLEXES

Reflexes are graded in two ways. The numerical evaluation is widely accepted at 0 being absent, 1 being decreased, 2 being normal, 3 being increased and 4 being clonic. Another option is to simply use the terms themselves: clonic, normal, decreased and absent. Stay consistent in your choice.

Biceps Reflex

Evaluating the musculocutaneous nerve, spinal cord segments C6 – C8, and the biceps brachii muscle. Musculocutaneous nerve (spinal cord segments C6, C7, & C8).

How do you test for:

The biceps are a flexor so ensure it is in extension by holding limb extended at elbow and drawn backwards a bit. Place finger on the biceps brachii anteromedially to the elbow tendon insertion and gently tap finger with pleximeter.

What do findings mean:

Brief contraction of the biceps brachii muscle results in slight flexion of the elbow.  Note a contraction of the biceps muscle and/or a twitch of the toes anteriorly

Triceps Reflex

Evaluating the radial nerve, the mid to caudal brachial plexus, spinal cord segments C7, C8, & T1(T2), and the m. triceps brachii. Radial nerve (spinal cord segments C7, C8, & T1(2)).

How do you test for:

The triceps is an extensor so the limb is held in flexion at the elbow, drawn anteriorly and slightly abducted to get the most tension on the tension insertion. Keep the limb somewhat relaxed to some degree while holding the position. To assess the phasic stretch reflex of the m. triceps brachii, the patient is placed in lateral recumbency with the thoracic limb being tested on the up side.  The limb should be as relaxed as possible and is supported with the elbow in flexion to put tension on the tendon of the triceps muscle complex.  The antebrachium should not be grasped since this will interfere with the expected reflex extension of the elbow

What do findings mean:

Brief contraction of the m. triceps brachii results in brisk but often subtle extension of the elbow.  Since the elbow extension might be too subtle to detect, the examiner can also use the supporting hand to directly feel for contraction of the m. triceps brachii.  Remember, many otherwise normal dogs will not have a triceps brachii muscle reflex. This is particularly true in large breed dogs.

Withdrawal reflex – nociceptive

Here the sensory component of the radial, median, and/or ulnar nerves depending on the site (usually between forelimb digits) chosen for noxious stimulation.  The motor components of nerves responsible for innervating thoracic limb flexors include the entire intumescence (spinal cord segments C5 – T1(2)).

How do you test for:

This is best assessed in lateral recumbency with a relaxed extended limb. Grab and pinch the web of the feet for sensory stimulus. Sometimes the examiner can pull the leg gently prior to pinching.

What do findings mean:

The initial reflex is manifest as rapid shoulder flexion and withdrawal of the entire limb.

Cutaneous trunci or panniculus – nociceptive

With this reflex, the examiner can determine the level of spinal cord damage based on the point at which a panniculus is elicited. The general somatic afferent fibers are contained within the dorsal branches of spinal nerves (C8/T1 through L3) that innervate the skin in overlapping dermatomes over the dorsolateral aspect of the torso. The tracts cross over and travel both ipsi and contralaterally. The efferent neurons exit the ventral gray columns of spinal cord segments C8 and T1 to innervate m. cutaneous trunci via the lateral thoracic nerve.

How do you test for:

Place the animal in a standing or sitting position.  Palpate the wings of the ilium and find the L7 spinous process.  Use a hemostat to pinch the skin just lateral (1-2 inches) to midline beginning at the level of L7 spinous process.  Continue cranially on the ipsilateral side to the next spinous process and repeat application of noxious stimulus; repeat this procedure until contraction of the cutaneous trunci muscle is noted.  Test the contralateral side.

What do findings mean:

Bilateral contraction of the cutaneous trunci muscle induced by noxious stimulation at the level of L7 spinous process.  The spinal nerve dermatome at which a noxious stimulus causes m. cutaneous trunci contraction indicates the first spinal cord segment cranial to the lesion.  However, a normal panniculus reflex does not rule out a lesion within the C8/T1 – L3 region; it may simply suggest that the lesion is not defined or severe enough to affect the fasciculus proprius.  With myelopathy at C8-T1 or nerve damage (brachial plexus avulsion for example) at these nerve roots, the motor response is absent.  Regardless of which side of the dermatome is stimulated, a unilateral lesion to the lateral thoracic nerve will result in contraction of m. cutaneous trunci on the side contralateral to the lesion.  Brachial plexus avulsion or damage to spinal cord segments C8 and T1 will cause this reflex to be absent at all levels.

Patellar reflex

Evaluate the femoral nerve, spinal cord segments L4-L6, and quadriceps femoris muscle. The function is extension.

How do you test for:

With the patient in lateral recumbency with the pelvic limb being tested on the up side, the stifle is flexed and should be as relaxed as possible.  The patellar ligament is then lightly tapped using the flat end of a reflex hammer.  The quadriceps femoris muscle should contract causing the stifle to briskly extend.  The patellar tendon tap reflex is the most reliable of all the muscle spindle reflexes that we examine.  To assess the tonic stretch reflex, palpate the quadriceps femoris muscle for tone and mass and passively manipulate the stifle.

What do findings mean

L4-L6 spinal cord segment or nerve lesions result in decreased or absent patellar reflex. Pseudohyperreflexia of the patellar reflex may be observed with lesions involving the sciatic nerve or its associated spinal cord segments L6 – S1(2).  These lesions result in loss of muscle tone to antagonists (flexors) of the quadriceps muscle group.  Therefore, the patellar reflex is hyperreflexic even without a true UMN lesion due to exaggeration of the quadriceps muscle contraction.  

Gastrocnemius reflex

The tibial branch of the sciatic nerve (one of the two terminal branches of the sciatic nerve), the spinal cord segments that supply the tibial nerve (L6 – S2), and the gastrocnemius muscle are evaluated. The sciatic nerve functions to flex the stifle and extend the hock.

How do you test for:

With the patient is placed in lateral recumbency with the pelvic limb being tested on the up side, the hip and stifle are extended and the tarsus is tightly flexed.  Use the flat end of a reflex hammer to tap the tensioned gastrocnemius tendon just proximal to its attachment on the tuber calcaneus.  

The gastrocnemius muscle and its synergists should rapidly contract to cause extension of the tarsus.  

What do findings mean:

Either a rapid contraction of the muscles that contribute to the gastrocnemius tendon (gastrocnemius, popliteus, superficial, and deep digital flexor muscles) and/or a slight extension of the tarsus and foot can be noted. Also, look for contraction of the caudal thigh muscles (semitendinosus and semimembranosus muscles) due to secondary spread of this monosynaptic reflex within the spinal cord to involve other branches of the sciatic nerve.

Withdrawal reflex

As with the thoracic limb withdrawal. The intumescence is involved but mostly the sciatic distribution (L6-S2) It is tested as the thoracic limb is tested.

Perineal reflex – nociceptive

The pudendal nerve and its branches (perineal and caudal rectal nerves), sacral (S1 – S3) and caudal (tail flexion) spinal cord segments, the cauda equina, and the external anal sphincter are evaluated. The sensory fibers are contained within the perineal branches of the pudendal nerve (spinal cord segments S1 – S3).  Constriction of the external anal sphincter is elicited by the caudal rectal branch of the pudendal nerve (S1 – S3).  Ventral tail flexion is mediated by the sacral (S1 – S3) and caudal spinal cord segments.

How do you test for:

Gently pinch the perineum (laterally, dorsally, and ventrally) with a hemostat or fingernails.  Observe reflex constriction of the external anal sphincter and ventral flexion of the tail elicited by noxious stimuli.

What do findings mean:

The segments of the cord and the nerves of S1-3 integrity is evaluated.  LMN damage will produce hypo- or atonia of the external anal sphincter and decreased to absent tail flexion following noxious stimulation of the perineum.  Involvement of the cauda equina will be manifest by flaccid paralysis of the tail, perineum, rectum, and bladder.  Overflow incontinence and fecal incontinence may result. Perineum should result in constriction of the external anal sphincter and ventral flexion of the tail.

Cross Extensor

This reflex is most often observed in the pelvic limbs, but can also occasionally be elicited in the thoracic limbs.  It is considered abnormal in a recumbent animal and indicates damage to UMN pathways.  However, the gray matter of the lumbosacral enlargement (L4 – S1(2)) must be intact for this reflex to be elicited in the pelvic limbs of a recumbent animal. The sciatic nerve (spinal cord segments L6, L7, & S1 (2)) supplies sensory and motor innervation necessary for flexion of the hock and stifle.  The femoral nerve (spinal cord segments L4, L5, & L6) supplies motor innervation for hip flexion.  The same nerves are responsible for extension of the contralateral limb.

How do you test for:

With the patient in lateral recumbency, both limbs are resting relaxed. The bottom limb can get gently extended and withdrawal response performed. As the animal pulls that leg up the upper limb will normally not move.   

What do findings mean:  

The crossed extensor reflex is considered normal in a standing animal because it serves as a mechanism by which one limb can provide greater weight-bearing support when the contralateral limb is flexed.  A normal animal in lateral recumbency will not develop extension of the up limb in response to noxious stimulation of the contralateral paired limb.  When the crossed extensor reflex is elicited, the up limb develops complete and involuntary extension in response to noxious stimulation of the down limb.  The crossed extensor reflex is normally inhibited through descending UMN pathways in a recumbent animal.  It reflects UMN disease.

 

PART V: PALPATION

The last segment of the exam is thorough palpation of all muscles and the spine.

Palpation of the cervical spine is done side to side, and up and down. It is also performed by isolating the upper and lower cervical spine. To evaluate the upper cervical spine, ne hand is placed as a fulcrum on the upper neck about the level of AA and AO and the opposite hand is used to move the muzzle around to the ipsilateral side of the hand and side of neck tested. Do not move the lower neck. Test other side.  For the lower neck evaluation, one hand is placed as fulcrum over the lower cervical spine just ahead of the shoulder and the opposite hand on the opposite side bracing head and upper neck. The motion is to pivot the neck towards the side being tested without moving the upper neck. The ventro and dorso flexion as done slowly and as a whole.

Palpation of the thoracic, lumbar and sacral spine is done by supporting the animal with one hand to avoid pressure over joints and with the other hand, apply pressure with downwards (examiner should not pinch the spine) straddling the spine and testing vertebra by vertebra. At the LS, the tail can be elevated fully to assess LS pain as well.