Skills Laboratory, Part 1: Performing a neurologic examination

Many veterinarians are uncomfortable when facing a patient with a neurologic problem. However, by taking the time to obtain a good, detailed history and by doing a methodical and thorough neurologic examination, these cases can be both challenging and interesting. In this article, I review the neurologic examination step by step and provide tips to help you better understand the significance of the abnormalities found. The next article describes how to interpret the results of the neurologic examination.

HISTORY

A good history is always important, but it is crucial when dealing with a neurologic case. In everyday practice, appointments are often booked every 10 to 20 minutes, so we tend to jump to the physical examination as quickly as possible. For a patient with a neurologic disorder, most of this time should ideally be spent collecting the history. If needed, do not hesitate to hospitalize the patient so you can do a complete neurologic examination and assessment later. Most clients will understand and appreciate that you are taking the time to listen to them and thoroughly evaluate their pets.

When listening to the history, try to separate the facts from the client's interpretation of the problems (Table 1). For example, many owners assume that their pets are in pain if their pets are having difficulty walking. However, an abnormal gait might be the result of a nonpainful condition that causes ataxia or weakness rather than pain. Most clients can readily identify problems or changes in their pets' behavior because they know their companions so well. However, their assessment of the problem's cause is not necessarily correct.

Table1. Clinical Signs and Possible Client Misconceptions

When questioning a client, be suspicious when, for example, he tells you that his 6-year-old golden retriever suddenly seems to be getting old. A middle-aged dog should not suddenly exhibit signs of old age; it could be mentally depressed or lethargic. Ask about the onset of the clinical signs (overnight or gradual over the past few days or weeks), the progression (better, worse, or stable), and the response to any treatment. Also ask clients about any change in behavior (hiding, sleeping more, pacing, confusion) and about their pets' activity (difficulty going up or down the stairs or jumping, shaking their heads). Difficulty going down the stairs or jumping off something is most likely associated with a problem of the neck, forelimb, or both, whereas a problem jumping on something or climbing the stairs is most often associated with a back or hindlimb problem (i.e. pain, weakness). A pet that is reluctant to shake its head or that refuses to flex its head to eat but will happily take food that is handed to it directly most likely has neck pain. You may need to ask the same question many times in different ways to obtain or validate the information. Also, don't push for a specific answer and always give the client the opportunity to answer "I don't know" without feeling negligent or guilty.

INITIAL OBSERVATIONS

While taking the history, look at the pet's behavior and attitude in the room. Most normal patients will hide or timidly explore the room. Try to determine what the normal behavior of that specific pet should be. For example, a puppy should move around and explore everything, whereas most cats will try to find a place to hide.

Have the patient walk freely (i.e. unleashed and on the floor) in the room while you take the history. This allows you to evaluate its gait without restraint as well as its behavior, mental status, and interaction with the surroundings and its owner. While the animal walks freely in the room, you may identify pacing, circling, bumping into things, or falling asleep in the middle of the room. Allow cats to jump if possible since this is a good way to evaluate their balance and strength. Perform a more complete gait evaluation during the neurologic examination.

NEUROLOGIC EXAMINATION

like to divide the neurologic examination into six sections: mental status, gait and posture, cranial nerves, spinal reflexes, conscious proprioception reactions, and other factors (e.g. evaluation of pain, tremors, seizures). (See the sample Neurologic Examination Form.)

Neurologic Examination Form

Mental status

Evaluate a patient's mental status while taking the history and making your initial observations. Take note of the client's evaluation, but also make your own assessment. A bright and alert pet with normal responsiveness has a normal mental status. A poorly responsive animal that is difficult to arouse but has a normal reaction to different stimuli (e.g. looks at owner and wags its tail when the owner calls its name) is lethargic or mentally depressed. The mental depression secondary to a brain lesion might be hard to differentiate from the lethargy secondary to a variety of other medical problems. The physical examination and the rest of the neurologic examination will help you differentiate between neurologic and other causes. A pet that can only be aroused by a strong stimulus such as pain is characterized as stuporous, whereas a pet that cannot be aroused at all is characterized as comatose.1 An animal with an improper reaction to stimuli is mentally confused.

Gait and posture

Evaluate the gait and posture on a nonslippery surface. A carpeted room or a hallway with a large rug is ideal. If needed, take the patient outside. Many neurologic abnormalities are more obvious when a patient walks slowly. So have the client walk the patient at different paces and in circles to improve your chance of defining the problem. Allow cats to jump on chairs or other furnishings while in the exam room. Also, do not assume that a pet is paralyzed because the client says so. Unless there is a possibility of spinal fracture, try to support the patient with a sling or a towel under the abdomen or even with a sling for the back and a harness for the front. Have the client step back and call for the pet to see if it wags its tail or moves its limbs voluntarily. You will gain important information by doing this with and without supporting the animal, since some pets will be inhibited by sling support.

First, assess whether the pet is ataxic. Evaluate whether the pet's feet are randomly placed on the floor or whether the gait is regular. Look for possible overreaching with the forelimbs, delayed protraction, hypermetria, and loss of balance. If the animal is ataxic, characterize the ataxia. Vestibular ataxia is characterized by a head tilt, a wide-base stance, and a loss of balance (e.g. falling to one side, leaning). The head is usually (but not always) tilted toward the side of the lesion. Sometimes, the body can be completely curved with the concavity on the side of the lesion. Cerebellar ataxia is characterized by dysmetria and a bouncing gait because of an inability to regulate the rate and force of movement.2 Hypermetria, or greater movement of the limb than normal, is most often recognized.2 It can be accompanied by intention tremors, which are fine tremors present on initiation of voluntary movements. They are particularly visible in the head, especially when the animal is trying to smell something or is reaching for food. These tremors are absent during sleep or complete rest. Strength is preserved with a pure cerebellar problem. Proprioceptive ataxia is almost always accompanied by some degree of paresis (weakness or partial paralysis) and is characterized by the body's tendency to deviate from the midline. Crossing of the limbs, dragging of the toes, knuckling (walking on the dorsal surface of the paw), overreaching, and circumduction can also be seen.

Once the presence and type of ataxia are determined, evaluate whether weakness or lameness is present. If you notice a gait abnormality, evaluate whether it affects only one limb, both hindlimbs, the ipsilateral limbs, or all four limbs. A marked asymmetry may occasionally be present, and, although only one limb may seem to be affected, carefully assess whether a subtle deficit is present in the contralateral limb. Keep in mind that a dog can get up and walk fairly well with only three limbs (e.g. a dog with an amputated limb). If you see a problem in one limb in an animal that can hardly walk without falling and needs help to get up, then most likely another limb (contralateral or ipsilateral) is affected also.

When describing ambulation, record the type of ataxia, if present, and the gait (normal, ambulatory paresis, nonambulatory paresis, paralysis) and limbs affected. Again, it is important to evaluate whether voluntary movements are present when a patient is nonambulatory by supporting the patient. If paresis is present, qualify it as upper motor neuron (normal to increased spinal reflexes and muscle tone) or lower motor neuron (absent or reduced reflexes and tone).

Cranial nerves

When evaluating the cranial nerves, it is important to differentiate between a reflex and a reaction. A reaction implies conscious manifestation and participation of the cerebral cortex.

The first cranial nerve, the olfactory nerve is an afferent nerve responsible for the perception of smell. It is rarely evaluated because of the difficulty in stimulating only one side at a time and because of the concomitant stimulation of the sensory fibers of the trigeminal nerve in the nasal mucosa when using a strong or irritating substance. Specific information from the owner (e.g. the pet does not smell its food) might be more helpful.

The second cranial nerve, the optic nerve, is the afferent nerve for vision and the pupillary light reflex (PLR). It is evaluated by the menace reaction and the PLR (see oculomotor nerve below). The menace reaction not only evaluates the second cranial nerve but also the ocular components, the optic chiasm and other structures of the visual pathway, the contralateral occipital cortex, and the ipsilateral cerebellum and facial nerve. Test the menace reaction by holding the pet's head, covering one eye with one hand, and making a forward gesture with the other hand (Figure 1). The expected response is closure of the eyelids, possibly accompanied by a backward movement of the head and retraction of the eye. When making the forward gesture, be careful not to get too close to the eye, as the air movement produced by the hand movement might stimulate the sensory fibers of the cornea and produce a false positive reaction. Remember that the menace reaction is a learned reaction and is absent in kittens and puppies up to about 12 weeks old.2

The oculomotor nerve, the third cranial nerve, is divided into a motor part bringing innervation to most extraocular muscles (dorsal, ventral, and medial recti and ventral oblique) and a parasympathetic part responsible for pupillary constriction. The motor part is evaluated by checking for physiological nystagmus (sometimes called doll's eyes or oculocephalic reflex) and strabismus. To test for physiological nystagmus, move the animal's head quickly from side to side while looking in the animal's eyes. Physiological nystagmus is characterized by a quick eye movement phase in the direction of the head movement and a slow phase in the opposite direction. When examining cats for physiological nystagmus, I prefer to hold them under their forelimbs and then turn myself in both directions with the cat facing me. Lesions of the oculomotor nerve will cause a fixed, ventrolateral strabismus (Figure 2) along with a lack of conjugate nystagmus. The third cranial nerve also innervates the levator palpebrae muscle, and a lesion may cause ptosis. The parasympathetic part of the third cranial nerve is the efferent part of the PLR. To evaluate the PLR, cover one eye, and use a powerful light such as a transilluminator or a good penlight to stimulate the tested eye (via the optic nerve) and look for the pupil's contraction (via the oculomotor nerve). Once the pupil is constricted, quickly move the light to the other eye to see if there is an indirect response as well. The contralateral pupil should already be constricted. Repeat on the other side.

1. Testing the menace reaction. 2. Direction of strabismus after cranial nerve involvement.

The trochlear nerve (fourth cranial nerve) and the abducent nerve (sixth cranial nerve) are also assessed as part of the physiological nystagmus and strabismus evaluation. The trochlear nerve innervates the dorsal oblique muscle of the eye. A lesion involving this nerve causes a lateral, rotational strabismus (Figure 2). In dogs, a retinal examination is necessary to evaluate the rotational strabismus associated with trochlear nerve involvement since the pupils are round and, thus, a rotational strabismus cannot be seen. The abducent nerve innervates the lateral rectus muscle of the eye. A lesion involving this nerve will cause a medial strabismus (Figure 2). The abducent nerve is also responsible for the retraction of the eyeball in the orbit (innervation of the retractor bulbi muscle), and this can be tested by gently touching the cornea with a finger or a moist cotton swab.

The trigeminal nerve, or fifth cranial nerve, is divided into a motor part and a sensory part. The motor part (mandibular branch) innervates the masticatory muscles and is evaluated by palpating the temporal and masseter muscles on both sides and by assessing the patient's ability to close its mouth. The sensory part is evaluated by assessing the palpebral reflex and the nasal sensation reaction. For the palpebral reflex, gently touch the medial canthus (ophthalmic branch), lateral canthus (maxillary branch), and base of the ear and the jaw (mandibular branch). The efferent part of the reflex is mediated by the facial nerve and results in eyelid closure. The nasal sensation reaction is tested by touching or poking the upper lip, nasal septum, or both to elicit a reaction from the patient (Figures 3 & 4). In addition to eyelid closure (reflex portion), you should see an aversion reaction (e.g. backward movement of the head, licking of the nose). This reaction requires not only trigeminal sensory function but also good function of the contralateral somesthetic cortex of the brain.

3 & 4. Testing nasal sensation

The facial nerve, the seventh cranial nerve, innervates the muscles of the face. It is responsible for facial expression (absence of innervation causes a droopy face, dropping or absence of ear movement) and eyelid closure. When evaluating eyelid closure, make sure that the closure is complete by gently passing your finger along the eyelids' surfaces since a facial paresis might be missed otherwise.

Like its name indicates, the vestibulocochlear nerve, or eighth cranial nerve, has two parts. The vestibular component is responsible for balance, and the cochlear part is responsible for audition. It is difficult to evaluate the cochlear part objectively without using a specific diagnostic procedure (brainstem auditory evoked potentials). The vestibular part is evaluated by assessing for the presence of a head tilt, loss of balance, and pathological nystagmus (i.e. nystagmus present in the absence of any head movement). In cases of peripheral vestibular disturbance, pathological nystagmus can be horizontal, rotary, or both, and the fast phase is in the opposite direction of the head tilt. Pathological nystagmus can be present all the time (resting) or can be induced by holding the head in lateral flexion or full extension (positional).2 The latter is usually seen in cases of less severe involvement or after a few days and suggests a certain compensation of the vestibular system. When a vertical nystagmus is present, when the fast phase is toward the side of the head tilt, or when the direction of the nystagmus changes direction with alteration of the head's position, a central involvement (brainstem or cerebellum) must be suspected. In cases of severe, bilateral vestibular involvement, nystagmus (either physiological or pathological) is usually not seen. Instead of a head tilt, head movement from side to side might be seen.

The glossopharyngeal and vagus nerves, the ninth and 10th cranial nerves, are usually evaluated together. Most of the time, important information regarding their function can be obtained from the history by asking about any difficulty swallowing, upper respiratory noises, change in voice, or regurgitation. The gag reflex should be evaluated with extreme caution or not at all in aggressive animals. In cooperative patients, a swallowing reflex can be induced by touching the pharynx with a tongue depressor or something similar. Valuable information can also be obtained by offering food or water and looking at the swallowing process.

The accessory nerve, the 11th cranial nerve, is evaluated by palpating the neck and shoulder area. This nerve innervates the trapezius, sternocephalic, and brachiocephalic muscles. Involvement of the accessory nerve can cause muscle atrophy.

The hypoglossal nerve, the 12th cranial nerve, innervates the tongue. To evaluate it, open the patient's mouth, and look for signs of atrophy or asymmetry. Try to have the patient lick its nose on both sides; you might have seen this when evaluating the nasal sensation reaction. You can also put a little food on the patient's nose to stimulate licking.

Spinal reflexes

The spinal reflexes can be qualified as normal (+2), increased (+3), clonic (+4), reduced (+1), or absent (0). Normal to increased muscle tone and reflexes are a sign of upper motor neuron involvement, whereas reduced to absent reflexes are a sign of lower motor neuron involvement. Because the separation between normal and increased can be subjective, especially in a nervous patient in which the reflexes might seem falsely increased, and because this differentiation does not change the interpretation of the lesion's location, I rarely try to differentiate between the two.1

The most, and sometimes only, reliable tendon reflex is the patellar reflex.2 The flexor (withdrawal), perineal, and cutaneous trunci reflexes should also be evaluated. With the animal in lateral recumbency, start by palpating the muscles and joints for any evidence of pain or swelling. Also evaluate the muscle tone while the patient is in lateral recumbency by feeling the resistance of the limb to manipulation or a pressure of the hand over the plantar or palmar surface of the paw (Figure 5). For the patellar reflex, gently but firmly tap the patellar tendon. Both the afferent and efferent pathways of this reflex are mediated through the femoral nerve (L4-L6 segments of the spinal cord). The effector muscle is the quadriceps femoris, and the stifle should extend. I like to elicit the reflex on both the recumbent and nonrecumbent sides. In a tense animal, the recumbent limb is usually more relaxed, so it may be more reliable for evaluating the patellar reflex. Be cautious in your interpretation in patients that are excessively tense and holding their limbs in extension. It might lead to a falsely reduced or increased reflex. Be aware that some dogs will eventually lose their femoral reflex as they age.3 It may not be possible to elicit the reflex in dogs with previous orthopedic problems such as an anterior cruciate ligament rupture.4

The flexor reflex is evaluated by pinching both the lateral and medial toes at the base of the nail of the nonrecumbent limb. Complete limb flexion is expected (Figure 6). The afferent pathway of the reflex is mainly from the sciatic nerve and part of the femoral nerve on the medial toe, and the efferent pathway evaluates the integrity of the sciatic nerve (L6-S1 segments of the spinal cord). When evaluating the flexor reflex, make sure that there is maximal flexion of all joints before concluding that the reflex is normal. In many patients with sciatic paresis (e.g. polyneuropathy, lumbosacral compression), flexion of the hocks might be incomplete. Because marked joint pain can result in poor flexion and lead to a wrong assessment, it is important to evaluate the limb for any sign of pain before testing the flexor reflex by performing a good orthopedic examination.

5. Evaluating muscle tone. 6. Testing the flexor reflex.

For the thoracic limbs, the most reliable myotatic reflex is the extensor carpi radialis. With the patient in lateral recumbency, support the nonrecumbent thoracic limb at the level of the elbow. With the elbow and carpus in slight flexion, strike the extensor carpi radialis muscle with a plexor. A slight extension of the carpus is expected, although it cannot be elicited in some patients. The afferent aspect of the extensor carpi radialis reflex is mediated mainly by the radial nerve for the medial toe and the ulnar nerve for the lateral toe. A complete and prompt normal reflex requires the proper function of many nerves of the brachial plexus coming from the C6-T2 segments of the spinal cord (axillary, musculocutaneous, median, ulnar, and radial nerves). Other tendon reflexes can be evaluated, but they are not always reliable.2 A good description of these reflexes can be found elsewhere.1

The perineal reflex is evaluated by gently touching the perineal area with a pin or forceps (the afferent pathway is the pudendal nerve). The normal response is flexion of the tail and contraction of the anal sphincter mediated by the S1-S3 and caudal segments of the spinal cord. Evaluate the reflex on both sides.

The cutaneous trunci reflex allows evaluation of the superficial sensation of the thoracolumbar spinal cord along with the cutaneous trunci muscle, innervated by the lateral thoracic nerve (spinal cord segment C8-T1). The afferent nerve comes from the stimulated segment, enters the spinal cord at the level of the stimulation, and travels cranially (bilateral). A synapse occurs at C8-T1 causing a bilateral contraction of the cutaneous trunci muscle. With the animal standing or in sternal recumbency, gently pinch the skin lateral to the spine from caudal to cranial. As mentioned previously, the stimulation of one side should stimulate a bilateral contraction of the cutaneous trunci muscles. In cases of a unilateral C8-T1 involvement, the cutaneous trunci reflex will be absent unilaterally on the side of the lesion, regardless of the side of the stimulation. In cases of a transverse myelopathy, the cutaneous trunci reflex may be absent bilaterally, caudal to the lesion. In normal animals, the reflex gradually disappears in the middle to lower lumbar area. It can be difficult to elicit in some animals, especially in cats.2

Conscious proprioception reactions

You first evaluate the conscious and unconscious proprioception while evaluating the gait (e.g. knuckling, dragging of the toes); however, it is worth further evaluation. Conscious proprioception is a reaction and, thus, requires normal function of all the ascending and descending pathways in the spinal cord up to the contralateral somesthetic cortex. In dogs, evaluate conscious proprioception with the animal standing. For the hindlimbs, I like to support the patient's weight under the pelvis and gently place the foot on its dorsal surface (Figure 7). A normal patient will quickly and properly replace the foot on its plantar surface. Some animals are more relaxed with support under the abdomen. Also, a submissive or painful dog may be slow to replace the limb even if the proprioceptive pathway is intact. For the forelimb, I like to stand over the dog and support the patient under the chest with one hand (Figure 8). Gently place the front paw on its dorsal surface. It is not unusual that a pet won't let you place the dorsal surface on the floor before attempting to replace it.

While in this position, have the dog hop from side to side by holding the back end and one forelimb up without supporting all the weight and pushing the animal laterally on the side of the tested limb (Figure 9). This evaluates both conscious proprioception and strength since the weight of the dog is shifted to the tested side. Because motor function is also evaluated by these manipulations, it will be necessary to support the weight to really evaluate the proprioception component in a weak animal. When evaluating hopping and placing reactions, poor initiation of the movement suggests a sensory (proprioceptive) deficit, whereas poor performance of the movement suggests a motor problem.

7-9. Evaluating conscious proprioception.

In cats, conscious proprioception reactions are best evaluated with hopping, wheelbarrowing, and nonvisual tactile placing. The wheelbarrowing reaction is evaluated by supporting the patient under its abdomen and lifting its hindlimbs so that all its weight is supported by the forelimbs. A normal animal should be able to walk forward and from side to side. Be careful not to elevate the hindlimbs too much since it may result in an abnormal body posture. The extensor postural thrust reaction is somewhat similar and is used to test the hindlimbs. To evaluate it, support the animal by the thorax, just caudal to the forelimbs, and gently lower it until its hindlimbs touch the floor. A normal animal will move its limbs caudally in a walking motion as it touches the floor to gain normal support. Nonvisual tactile placing is evaluated by supporting the patient under the thorax while covering its eyes and bringing the forelimbs (at or distal to the carpus) in contact with the edge of a table, one at a time. The normal reaction is for the animal to place its foot on the surface of the table immediately after contact with the table. Be careful not to restrict the patient's movement while testing because it can result in a lack of reaction.

Other factors

As part of the neurologic examination, you should also evaluate the muscle mass of the head, limbs, and trunk. I like to evaluate the muscle mass while the animal is standing, just before I evaluate conscious proprioception. I also evaluate the muscle tone of the tail. Any asymmetry is often more informative than a bilateral, symmetric atrophy. Neuropathic atrophy can be identified as quickly as seven to 10 days after the insult, whereas disuse atrophy will be apparent after a few weeks.

Evaluate deep pain perception in all paralyzed dogs. Deep pain perception is not a reflex, so we want to see a reaction from the animal (e.g. turns its head, cries, tries to bite). If the superficial pain perception is intact, then the deep pain perception will be as well. When testing for deep pain perception, apply a strong pressure at the base of the third phalanx with forceps. Limb flexion is only a reflex (flexor reflex) and should not be interpreted as a sign of positive deep pain perception.

Finish your examination by evaluating the animal for a painful area. For the cervical spine, I find that observation of the animal and manipulation of the neck are more informative than palpation of the spine (the spine being ventral to a large muscle mass in that area). Do not move the neck if a spinal fracture or an atlantoaxial instability is suspected. Also, neck manipulation is not necessary if obvious neck pain is noted on simple observation of the animal (e.g. the pet screams when it moves its neck itself, the pet holds its neck still and looks around by moving its eyes only, or muscle spasms can be seen in the neck). If there is no risk of fracture or instability and if pain is not evident, gently move the neck from side to side and up and down and note any pain or resistance. Try to reduce the stress of the patient by talking or rubbing its ears while doing this. You can also move a toy or some food around the animal's head to evaluate the range of movement. Open the mouth to identify pain from the temporomandibular joints or tympanic bulla area, and then palpate the thoracic and lumbar spine by using moderate pressure with one finger on each side of the spine. For the lower back and lumbosacral area, elevating the tail and extending the hips (avoid the latter in dogs with known painful hips or hip dysplasia) can help identify pain in addition to applying digital pressure to the lumbosacral area. Dorsal pressure through rectal palpation can be useful in identifying lumbosacral pain.5,6

Before making your final assessment of the lesion's location, make sure to note any other abnormalities in the animal, such as generalized tremors or seizures.

CONCLUSION

Performing a neurologic examination is not difficult and can be easily included as part of your physical examination. The tricky part is the proper evaluation and interpretation of the findings (see the article "Skills Laboratory, Part 2: Interpreting the results of a neurologic examination"). As it is when performing a physical and orthopedic examination, it is important to be familiar with what is normal in dogs and cats before deciding what is abnormal in a given patient.

Veronique Sammut, DVM, DACVIM (neurology)

California Animal Hospital

1736 S. Sepulveda Blvd.

Los Angeles, CA 90025

REFERENCES

1. Lorenz MD, Kornegay JN. Handbook of veterinary neurology. 4th ed. St. Louis, Mo: WB Saunders, 2004.

2. de Lahunta A. Veterinary neuroanatomy and clinical neurology. 2nd ed. Philadelphia, Pa: WB Saunders, 1983.

3. Levine JM, Hillman RB, Erb HN, et al. The influence of age on patellar reflex response in the dog. J Vet Intern Med 2002;16:244-246.

4. Olby NJ. Decreased mobility in old dogs: Causes and treatment, in Proceedings. Forum Am Coll Vet Intern Med, 2004.

5. Sharp NJH, Wheeler SJ. Small animal spinal disorders: Diagnosis and treatment. 2nd ed. St. Louis, Mo: Mosby, 2005.

6. Muñana KR. Canine and feline myelopathy, in Proceedings. West Vet Conf, 2002.

SUGGESTED READING

1. Chrisman CL, Mariani C, Platt S, et al. Neurology for the small animal practitioner (made easy series). Jackson, Wyo: Teton New Media, 2002.

2. Chrisman CL. Problems in small animal neurology. 2nd ed. Portland, Ore: Lea & Febiger, 1991.

3. Vite CH, Braund KG. Braund's clinical neurology in small animals: Localization, diagnosis and treatment. Available at: www.ivis.org. Accessed 2003.