The neurological exam seems to be one of the most confusing concepts in veterinary medicine. Let’s try to clarify things. To simplify, we will focus on the hind legs only.
One way to look at the neuro exam is to divide it into an assessment of “the four stages” and an evaluation of four reflexes.
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| The patellar reflex causes extension of the stifle. Photo courtesy of Dr. Phil Zeltzman. |
The four stages require a functional spinal cord and a functional brain, and they help us determine a lesion’s severity. Reflexes tell us only where the lesion is localized.
Since I am a surgeon and not a neurologist, I talked to Todd Bishop, DVM, Dipl. ACVIM (neurology), of Upstate Veterinary Specialties in Latham, N.Y., to ensure the accuracy of the following information.
Decline Into Nociception
Patients might go through four stages between normalcy and being paralyzed with no deep pain:
- First-stage patients may feel back pain. They can exhibit pain by vocalizing. Certain breeds, such as beagles, are especially good at expressing their feelings. Others may arch their back.
. - As they get worse, patients may become ataxic or lose proprioception. When a patient knuckles, or doesn’t reposition a flipped paw within a couple of seconds, we say he has proprioceptive deficits.
. - The next step is loss of conscious motor function. This means voluntary motion of the hind legs is weak, even if helped by a sling.
. - The last step is loss of pain sensation, or nociception. It is tested by using a hemostat to pinch a toe. Though nobody enjoys performing this test, doing it correctly is critical. We are trying to cause a painful reaction by stimulating the periosteum of the phalanges.
When a deep pain sensation is present, the patient should have a voluntary reaction such as whining, trying to bite or moving away from the painful stimulus. A very stoic patient may show only dilatation of the pupils.
The order of these four stages is fixed. They occur in the same order and always return in the reverse order. Therefore, there is no need to crush a toe in a patient who has motor function. If he has motor function, he has deep pain by definition. Purists will argue that this is not true with a “spinal walker,” but let’s keep things simple.
The Spinal Cord
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| The cranial tibial reflex causes flexion of the hock. Photo courtesy of Dr. Phil Zeltzman. |
Incidentally, these four stages correlate with the anatomy of the spinal cord. Nerve fibers involved with proprioception are located superficially in the cord. This explains why a mild lesion has mild effects on the patient.
A deeper lesion will affect the nerve fibers that control motor function. And a very severe lesion will apply pressure in the deepest nerve fibers—those that relay deep pain.
These four stages help us determine the severity of the lesion. A dog with proprioceptive deficits is mildly affected. At the other end of the spectrum, a dog with n...
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