The Neurologic Examination
Karen Kline, DVM
The neurologic examination is the cornerstone of the evaluation of the patient with neurologic disease. Components of the neurologic examination include the evaluation of mentation, cranial nerves, gait, proprioception, the motor system and the sensory system.
Mentation of the patient includes their content of consciousness (the mediated through the cerebral cortex) and the level of consciousness (mediated through the brainstem). The content of consciousness of the patient includes whether or not that animal is appropriate for its surroundings, is agitated or reticent, aggressive or timid. Changes in habits, pacing, inappropriate elimination and a change in sleep-wake patterns can all indicate that the patient may have disease of the cerebral cortex or forebrain. The level of consciousness of the patient is regulated thorough the brainstem which is composed of the activating reticular system (the rudimentary alerting system), the midbrain, pons and medulla (which house the ascending sensory and descending motor pathways, the cranial nerve nuclei and their corresponding peripheral nerves (CNN I-XII).
The cranial nerves are all paired and there are a total of 12 pairs. A pen light is used to assess the pupillary light response (PLR-CNN II, III) and to assess for Horner's syndrome and /or anisocoid. A complete fundoscopic examination is essential to differentiate between ophthalmic and cerebrocortical disease. The cranial nerve evaluation also assesses the palpebral reflex (CNN V, VII), the retractor bulbi reflex (CNN V, CNN VI), and vestibulocular reflexes (CNN III, IV, VI and VIII). Facial symmetry (CNN VII) and facial sensation (CNN V) should also be assessed. Nystagmus should also be evaluated in terms of character (horizontal, rotary and vertical downbeat) and whether or not it changes with a change in position.
Gait is evaluated by observing the patient attempt to walk or trot. It is important to delineate whether the gait disturbance is due to an orthopedic or neurologic cause. Once a neurologic cause has been determined, the gait disturbance may be determined to be sensory in origin (ataxia). There are 3 different types of ataxia: 1) Vestibular, 2) Cerebellar, and 3) Proprioceptive. An animal with vestibular ataxia may have a head tilt, roll, list or lean to one side or both sides. The may exhibit a "drunken sailor" type gait disturbance. A patient with cerebellar ataxia may exhibit a goose-stepping or dysmetric gait either unilaterally or bilaterally, and may exhibit head tremors. A patient with proprioceptive ataxia may knuckle-scuff the nails or cross over in the front or hind limbs.
Postural reactions involve the patient's ability to now where their limbs are in space. One can test the patients' proprioception by turning the foot over and observing whether or not it is replaced in the correct position. Proprioception can be abnormal with cerebral, brainstem or spinal cord disease.
The motor system can be evaluated by observing whether or not the patient can support weight against gravity. Paresis (weakness) implies an inability to support weight and may involves a short, choppy gait and a crouched gait. Paralysis (plegia) implies a complete loss of voluntary motor activity. Myotatic reflexes of both the front and hind limbs can be assessed by evaluating the extensor carpi radialis and triceps reflexes (radial nerve) in the front limbs and the patellar (femoral nerve) and cranial tibial reflexes (sciatic reflexes) in the hind limbs. The withdrawal reflexes can also be assessed in the front and hind limbs; and can be used to evaluate the brachial (front limbs) and lumbosacral (hind limbs) plexi.
The final evaluation of the neurologic examination involves the sensory system. Starting at the head and working caudally, the head and the ventral aspect of the neck and cervical vertebrae are palpated and evaluated for pain and hyperpathia. The dorsal spinous processes are palpated cranially to caudally. The tail is hyperextended and rectal examination is performed. If the patient is paretic or plegic, conscious pain perception should be evaluated. It is important to note that conscious proprioception is lost first, voluntary motor second, superficial pain third and deep pain last in spinal cord disease. Superficial pain is evaluated by taking the tips of the hemostat and pressing down on the toe webbing. Deep pain is assessed by taking the inside portion of the hemostats and pressing down on the toe of the patient. In both cases, the animal should turn around and acknowledge the noxious stimulus by trying to bite, raising its heart or respiration rate, or vocalizing. At this point, once the neurologic examination is complete, a neurolocalization can be made and the patient can undergo further diagnostics.