Charcot-Marie-Tooth disease

Diagnosis and Testing

Is there more than one test for Charcot-Marie-Tooth disease?

A doctor may suspect a diagnosis of Charcot-Marie-Tooth (CMT) disease because of certain symptoms. These signs can include muscle weakness particularly of the legs, difficulty lifting the feet when walking, or a loss of reflexes in the legs. Physical signs like toes that are curled so that the middle knuckle in rounded up (hammer toes), or a high arch to the bottom of the foot may also be seen.

Two tests that may be ordered are the nerve conduction velocity test and an electromyogram. These tests tell the doctor how well the motor or sensory nerves function. Motor nerves cause muscles to contract and allow people to perform voluntary functions like walking or talking. Sensory nerves have cells, or receptors, that respond to stimuli and send information to the brain. For example, in the skin they respond to touch, pressure, vibration, temperature, and pain.

A nerve conduction velocity test is when the motor and sensory nerves are electrically stimulated so doctors can determine how well the nerves pass along nerve impulses. Doctors will place an electrode on a motor or sensory nerve and stimulate the nerve with a small electric charge that can cause mild discomfort. How the nerves respond to this electric charge will be recorded and evaluated to see how well the nerves pass along nerve impulses.

An electromyogram records the electrical activity of muscles when they are at rest and when they are being used. This test uses a needle electrode, which is a very thin wire through which doctors can send an electrical charge. The needle electrode is inserted through the skin into the muscle where it can record the electrical activity of the muscle.

Some forms of CMT can be diagnosed through genetic testing. These tests involve studying the genes known to cause specific forms of CMT, like the PMP22 and MPZ genes, for mutations or other changes. Doctors do not know the underlying genetic cause of all forms of CMT, so these tests cannot confirm a diagnosis for everyone with CMT.

Charcot-Marie-Tooth Disease Fact Sheet. The National Institute of Neurological Disorders and Stroke website.

Bird TD. Charcot-Marie-Tooth Hereditary Neuropathy Overview. GeneReviews website.

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