Skills Laboratory, Part 1: Performing a neurologic examination - Veterinary Medicine
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Skills Laboratory, Part 1: Performing a neurologic examination
Take your time and be thorough, advises this author-neurologist, who tells you step by step how to examine a patient with a possible neurologic problem.


VETERINARY MEDICINE


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


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Source: VETERINARY MEDICINE,
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