Neurologic Examination and Lesion Localization

1 Neurologic Examination and Lesion Localization



Karen Dyer Inzana



1. Where do I start when performing a neurologic examination?

Always start by looking at the animal across the room. Look for abnormal body postures (i.e., head tilt or turn), abnormal movements (circling, head tremors), or behaviors that you would not expect from an animal in the hospital environment (dementia, excessive solumnence or extreme agitation). If any of these things are observed, then the problem must involve the brain lesion (above the foramen magnum).


2. How will changes in gait help localize lesions?

After observing the animal across the room, next watch the animal walk, preferably on a nonslippery surface. Look again for abnormal head postures or movements, but then concentrate on gait. Is there one side that appears weaker than the other? Is there a similar amount of coordination in the front and rear limbs? If the front limbs are abnormal, are they more or less abnormal than the rear limbs? Because the brachial intumescence in most dogs is located between C6 to T2 spinal cord segments, normal to near normal gait in the front limbs with poor coordination in the rear limbs suggests a lesion caudal to the second thoracic spinal cord segment (T2). If the front limbs are as weak or weaker than the pelvic limbs, then the problem likely resides within the cervical intumescence. If the front limbs are abnormal, but appear stronger than the pelvic limbs, this usually indicates a lesion rostral to C6. If one side (thoracic and pelvic limbs) appears weaker than the other (hemiparesis), the same rules apply as previously described, but one side of the spinal cord or brain is more severely affected than the other.


3. How can you be sure that an abnormal gait is caused by neurologic disease rather than an orthopedic condition?

Sometimes it can be difficult to differentiate between neurologic and orthopedic diseases. The best way to do this is with a series of tests referred to as postural reactions. Postural reactions are a series of maneuvers that place the animal’s feet in an abnormal position to bear weight. The animal must first recognize that the foot is in an abnormal position (sensory systems) and then have the strength to replace the foot in a more normal position (motor systems). Animals with orthopedic disease can accomplish most postural reactions. Occasionally animals with orthopedic disease will resist the postural reactions that require a lot of movement on the weight-bearing limb (e.g., hemiwalking, hopping, wheelbarrowing). However, it is extremely rare that all postural reactions are abnormal in an animal with only orthopedic disease. The following are the more common postural reactions.


• Conscious proprioception: Gently support the animal’s weight and turn one foot onto its dorsal surface. I place a hand under the pelvis when evaluating the pelvic limbs, and under the chest when examining the thoracic limbs. All four limbs should be examined. A normal response is to immediately flip the paw over onto the normal weight-bearing surface. Abnormal responses include leaving the foot in the abnormal position, repositioning it slowly or repositioning it incompletely (i.e., leaving one or more toes turned over).

• Wheelbarrowing: Support the animal’s pelvic limb with all of the weight on the thoracic limbs. Push the animal forward so it must take several steps with the thoracic limbs to maintain balance. This is often accomplished first with the head and neck in a normal position, then repeated with the head and neck elevated. Abnormal responses include delayed positioning of one or both thoracic limbs or exaggerated placement. Exaggerated placement may suggest an abnormality in the cerebellum or caudal brain stem.

• Extensor postural thrust: Lift the animal off the floor and gently lower it onto the pelvic limbs. A normal animal will often extend the limbs in anticipation of contact and then take several steps backwards to position the limbs correctly. An alternative technique for dogs that are too big to be picked up is to lift the front legs and push them backwards. I have rarely found this alternative helpful.

• Hemistanding and hemiwalking: Lift both front and rear limbs on one side so that one side supports all of the animal’s weight. Most normal animals can then accomplish lateral hopping movements with the supporting limbs.

• Hopping: This reaction is similar to hemiwalking, but all of the animal’s weight is concentrated on one limb. Again, normal animals can make lateral hopping movements in the one supporting limb.

• Visual and tactile placing: For small animals that are easily supported, bring the animal close to a tabletop while the examiner supports most of its weight. A normal response is for the animal to see the table and reach for it with the closest limb. A similar tactile response can be elicited by covering the animal’s eyes and advancing the animal so one limb brushes the side of the table. Again, a normal animal will attempt to place the limb in a position to bear weight.

4. When do you test spinal reflexes?

After completing the postural reactions, I have a good idea if the gait abnormality is orthopedic or neurologic in origin. If it is neurologic, I use the same information regarding localization of gait abnormalities that I described previously. Spinal reflexes help determine if the problem involves the intumescence (either cervical or pelvic) or is “upstream” of the intumescence. As previously mentioned, the cervical intumescence resides within spinal cord segments C6-T2, whereas the pelvic intumescence resides within spinal cord segments L4-S3. The intumescences contain the cell bodies for the lower motor neurons that innervate the thoracic or pelvic limbs, respectively. Injury to the lower motor neurons will cause spinal reflexes to be decreased or absent. Because the predominate clinical feature is caused by injury to the lower motor neuron, paresis or paralysis with decreased or absent spinal reflexes is frequently referred to as lower motor neuron clinical signs. Alternatively, if the lower motor neuron is intact but the problem resides in one or more neurons upstream or closer to the motor center in the brain, then spinal reflexes will still be intact and may be exaggerated even though the animal has lost some or all voluntary motor ability in that limb. Paresis or paralysis with normal to increased spinal reflexes if often referred to as upper motor neuron clinical signs that reflect that the injury is upstream from the lower motor neurons.


5. Do spinal reflexes help distinguish between neurologic and nonneurologic diseases?

Rarely. Postural reactions do a better job of answering the question, Is the problem neurologic or nonneurologic in origin? Spinal reflexes are strongly influenced by the temperament and anxiety level of the animal. If the animal is anxious, then the muscles are tense, and spinal reflexes often will appear exaggerated in an otherwise normal animal. If reflexes are abnormal, I will repeat postural reactions. It would be most unusual for neuronal injury severe enough to cause abnormal spinal reflexes to not also affect postural reactions.


6. Is it correct that spinal reflexes primarily distinguish between upper motor neuron and lower motor neuron injury?

Yes, this is the primary value of spinal reflexes in a neurologic examination.


7. How do you perform spinal reflexes and what should they look like?

Thoracic limb reflexes include the following:


• Flexor reflex, withdrawal reflex, pedal reflex: Pinching the toe (or other noxious stimuli) causes prompt flexion or withdrawal of the limb. The afferent branch varies with the area pinched; the efferent nerves are those that mediate flexion of the limb (axillary, musculocutaneous, median, and ulnar).

• Biceps reflex: This reflex is initiated by percussion of the biceps tendon (near its insertion on the craniomedial aspect of the forearm) and both afferent and efferent axons are carried in the musculocutaneous nerve (spinal cord segments C6-C8). The appropriate response is flexion of the elbow. However, this is often hard to see when holding the limb, so often you only see a visible contraction of the biceps muscle.

• Triceps reflex: This reflex is initiated by percussion of the triceps tendon near the olecranon. Both afferent and efferent axons are carried in the radial nerve (spinal cord segments C7-T2) and the appropriate response is extension of the elbow. This is the most difficult reflex to see in the front leg.

• Extensor carpi radialis response: Percussion directly over the belly of the extensor carpi radialis elicits extension of the carpus. Whereas they are both direct effects on the skeletal muscle and stimulation of stretch receptors (and associated myotatic reflex), a normal response requires an intact radial nerve. The appropriate response is extension of the carpus.
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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Neurologic Examination and Lesion Localization

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