Diagnosing CMT
by Dorothy B. Gosling, Reg. N.

I was diagnosed with CMT at the age of 35. Having had symptoms all my life, they became a problem at this age. I had an EMG and many blood and urine tests before the diagnosis was reached. I never did have a muscle biopsy even though I did not have a family history available. DNA testing was not available at the time and would have been useless if it had been because I have CMT type II.

When you visit your doctor with your medical complaints related to CMT, usually you will be referred to a neurologist. The common complaints are numbness, pins and needles (in a stocking and glove pattern), frequent tripping, ankle sprains and loss of balance.

Medical history

The neurologist will do your medical history, paying particular attention to your family history if it is available. Family members, who have similar symptoms to yours, may be asked to come in as well.

Physical examination

Then, you will be examined. The neurologist will pay particular attention to how you walk, whether you have high arches and other foot or hand deformities and whether your hands and/or legs are thin compared to the rest of your body. Your skin will be pricked very lightly with a pin, up and down your legs and arms, to determine if you feel the touch as sharp, dull or not at all. A piece of cotton or tissue may be used in the same way as the pin to find out if you feel soft touch. A tuning fork that is vibrating will be used on specific bony prominences (your elbows, wrists, hips, the outside of your knees, ankles, fingers and toes) and you will be asked if you feel the vibration, when it starts and when it stops.

Reflexes

Your reflexes will be tested: feet tested with a dull object that is run from your heels up the middle of the soles of your feet and across the balls of your feet quickly (the Plantar or Babinski sign); ankles (achilles), knees (patellar), wrists (brachioradialis), elbows (biceps) are tested with a reflex hammer; and abdomen (abdominal) tested by running an object quickly and lightly across the skin of your abdomen. These tests are done to find out if your reflexes are normal.

The Plantar or Babinski reflex causes your toes to automatically curl if it is normal. It is only abnormal when the brain or spinal cord are involved, so the results of testing this reflex are important in the diagnosis of CMT to rule out diseases in the brain.

In CMT type I, the ankle, knee, wrist, elbow reflexes are often absent; in CMT type II, the reflexes are sometimes slow but usually not absent.

Proprioception

You will have your toes and fingers moved up and down by the doctor, while your eyes are closed, to find out if you know which direction they are being moved. This tests for problems with balance and knowing where your body parts are without looking at them. Another test of your sense of orientation in space is standing with your feet right together and eyes closed. If you automatically sway or fall more than you do with your eyes open, then Romberg's sign is positive, which means you have difficulty knowing where parts of your body are and are having problems with balance.

Electrodiagnostic tests

Once the physical examination is complete, the doctor often will ask you to have an EMG or electromyogram done. There are two parts to this test. The first part tests your different nerves for their ability to carry messages to the muscles and the speed at which the messages are carried. This is called an NCV - nerve conduction velocity test. This test uses pads (electrodes), like a heart ECG, attached at specific points along the nerve and muscle and a very small electric shock is applied to measure the speed at which the shock travels to the muscle, causing the muscle to contract. This test is done on both motor nerves (MNCV) and sensory nerves (SNCV).

In CMT type I, nerve conduction speed is slowed. In CMT type II, the nerve conduction speed is usually normal or only mildly slowed but the responses to the stimulus are small. If you have a muscle disease, the nerve conduction speed remains normal.

The second part tests the ability of your muscles to respond to electrical impulses supplied by the nerves. This is the uncomfortable part. Very thin needles are inserted into each muscle, and the activity of the muscle is recorded on an oscilloscope (like a TV screen). The muscle activity produces a wave form which shows normal and abnormal muscle activity, the condition of your muscles, whether you have a muscle disease or a nerve disease, and the areas of your body that are involved.

Blood and urine tests

After your EMG is done, you may be asked to have blood tests and urine tests, specially if there is no family history. These tests are vital to the diagnosis because they will eliminate other treatable causes of your problem; for example: diabetes, vitamin B12 deficiency, heavy metal poisoning (e.g. lead), nutritional deficiencies and alcoholism. There are many diseases that mimic CMT which always need to be ruled out.

Biopsy

A muscle and nerve biopsy is the next thing the doctor may want done. A small piece of muscle and diseased nerve is removed and then examined under a microscope and can lead to a more definite diagnosis.

This test is not always advisable due to slower healing ability which sometimes comes with CMT. The area where the biopsy has been done may take a long time to heal and may be quite painful. Discussing this with your doctor prior to the test is important!

DNA testing

If the doctor has found an indication of a demyelinating disease on your EMG (the myelin sheath or covering of the nerve is not intact - imagine an electric cord with the plastic cover that has worn thin) or there is a suspicion that you may have pressure palsies or evidence that the disease was transmitted in a genetic X-linked pattern by family history, you may be asked to have DNA testing done.

The DNA testing which is currently available will only diagnose CMT1A, HNPP (hereditary neuropathy with liability to pressure palsies) and X-linked CMT. A DNA test procedure has been developed for CMT 1B; however, it is not widely available yet, as it is in the final testing stages. Therefore, presently available DNA tests will diagnose what is felt to represent about 80% of all CMT but are not useful to diagnose the other types of CMT, e.g. Type II, Type III, IV, etc. (Please see our Testing section under this topic for an update from Athena Diagnostics)

Putting it together

Once the doctor has put all this information together, he can then diagnose CMT because of the known characteristics of the disease. Depending on the severity of your symptoms and family history, often the doctor can tell you if you have CMT before completing all the tests. Make sure you ask questions of the doctor and find out why certain tests are necessary. Get all your questions answered… it is your body!

Editor's note: Please remember that diagnosing CMT isn't always easy. It takes a doctor, usually a neurologist who has seen people with CMT before and knows what to look for, to really get to the bottom of things. Expecting a general practitioner who might see one person with CMT every four or five years to immediately pick up on it is unrealistic. Asks your GP to refer you to a neurologist at a large medical facility where chances are they see more people with CMT. Don't be afraid to ask about the blood tests that, if positive, will bring your search for a definitive diagnosis to an end.