Making Sense of the Neuro Exam
By Phil Zeltzman, DVM, Dipl. ACVS
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.
|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
|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 no deep pain, to simplify, may have a poor prognosis.
Patients may go through these four stages very slowly—over weeks or months—or within days or even hours.
What Reflexes Show
Now we move on and test the patient’s reflexes. Many have been described. We will again simplify and focus on four common and simple reflexes:
- The patellar, or knee jerk, reflex is tested by stimulating the patellar tendon with a plexor, or hammer. A normal reaction is extension of the stifle. This is due to the femoral nerve, with nerve roots usually between L4 and L6.
- The cranial tibial reflex is elicited by percussion of the cranial tibial muscle. This should cause flexion of the hock via the peroneal nerve, with nerve roots usually between L6 and L7.
- The withdrawal, or flexor, reflex occurs after gently pinching or sometimes even touching the foot pads or toe web. Via the flexor muscles, the hip, knee and hock will flex with the help of the sciatic nerve. Its nerve roots are usually between L6 and S1.
- The perineal, or anal, reflex is tested by touching the left and right sides of the perineal area. When it is present, it causes contraction of the anal sphincter and flexion of the tail. It is mediated by the pudendal nerve, with nerve roots typically coming from S1, S2 and sometimes S3.
In Other Words
|Deep pain sensation is tested by using a hemostat to pinch a toe. Photo courtesy of Dr. Phil Zeltzman.|
With four simple reflexes, we can test the area between L4 and S3—the entire lumbosacral intumescence.
If the reflexes are normal or increased (hyper), the lumbosacral intumescence is normal and that’s not where the lesion is. The distinction between normal and hyper reflexes is somewhat irrelevant because it has the same meaning from a neurological point of view. The lesion is above the lumbosacral intumescence, between T3 and L3, which defines an upper motor neuron lesion.
If the reflexes are decreased (hypo) or absent, the lesion is within the lumbosacral intumescence—between L4 and S3. This means a lower motor neuron syndrome and has nothing to do with the prognosis. It helps us only to localize the lesion.
The controversy between deep pain sensation and withdrawal should not exist. Deep pain is one of the four stages. When it is absent, the prognosis may be poor. Withdrawal is merely a reflex, which helps us only to localize the lesion. So a patient can have excellent deep pain but a decreased withdrawal reflex, or vice versa.
Why is it important to understand the neuro exam and to be able to perform one? Well, besides the fact that it’s our job, it’s important because:
- It’s not rocket science.
- It helps us understand what’s wrong with our patient.
- It helps ruling out neurological vs. orthopedic conditions.
- It helps determine the prognosis, so we can guide our clients.
- It helps formulate a diagnostic plan. For example, it enables you to request an MRI of a specific spinal region, rather than asking “please MRI the spine.” You now can request an MRI of T3 to L3, or L4 to S1.
If the patient has a disc herniation, the lesion has an 85 percent chance of being located between T11-12 and L2-3. But keep in mind the many other possibilities, including tumors.
This is why it is preferable to study the whole area—T3 to L3 or L4 to S1. If in doubt, or if you are the surgeon who will need to count the vertebrae or ribs to plan the surgery, you can request a study of T1 to S1. <HOME>
Phil Zeltzman is a small-animal board-certified surgeon at Valley Central Veterinary Referral Center in Whitehall, Pa. His website is DrPhilZeltzman.com.
This article first appeared in the February 2010 issue of Veterinary Practice News
Because of an editing error, the captions for two photos were originally switched on Dr. Phil Zeltzman’s Surgical Insights column. The correctly labeled photos are shown here:
|The patellar reflex causes extension of the stifle.
||The cranial tibial reflex causes flexion of the hock.|
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