Diagnosis of CMT

CMT is usually first noticed when someone develops lower leg weakness and foot deformities such as foot drop, hammertoes and high arches, but that alone will not lead to diagnosis. A visit to a neurologist will start with a physical exam to look for further signs of distal weakness and sensory loss. To identify weakness, the patient may be asked to walk on his heels or to move part of his leg against an opposing force. Sensory loss is often identified when the doctor tests for deep tendon reflexes, such as the knee jerk, which are reduced or absent in CMT patients.

The doctor will also ask about family history. Since CMT is strongly hereditary, it is important to tell the doctor about any other family members with CMT-like symptoms. Lack of family history does not rule out CMT, but it will cause the doctor to look further to rule out other causes of neuropathy such as diabetes or exposure to certain chemicals or drugs.

Further testing may be electrodiagnostic, genetic, or both. Electrodiagnostic testing used to diagnose CMT usually includes a nerve conduction velocity test (NCV), which measures the strength and speed of electrical signals moving down the peripheral nerves. Delayed responses are a sign of demyelination (type 1) and small responses are a sign of axonopathy (type 2). An electromyogram (EMG) is also used to measure the electrical signal’s strength in the muscles of the arms or legs. NCVs and EMGs may cause mild discomfort and a topical anesthetic or mild sedative can be administered, especially if the patient is young and frightened of the procedure.

Generally, electrodiagnostic tests are performed by a neurologist or by a physician specializing in physical medicine and rehabilitation. Click here to find a physician who is board-certified to conduct needle EMGs and nerve conduction studies, or click here for more information about electrodiagnostic testing.

Genetic tests, done by drawing blood, are available to test for many, but not all, of the common chromosomal defects causing CMT. A positive genetic test can provide definitive diagnosis and provide useful information for family planning. However, a negative result does not rule out CMT since some forms cannot yet be tested by DNA sampling. Currently, 18 types can be identified by DNA testing: 1A, 1B, 1C, 1D, 1E, 1F, 1X, 2A, 2E, 2I, 2J, 2K, 4A, 4E, 4F, HNPP, CHN, and DSN. Click here to view a booklet on genetic testing and CMT prepared by Athena Diagnostics.

If genetic testing is recommended or desired, a patient’s physician can request a kit from Athena Diagnostics. The testing can cost several thousand dollars and may or may not be covered by a patient’s health insurance. Athena does, however, have a Patient Protection Program, which can limit a patient’s out-of-pocket cost to 20 percent of the total cost of the test. Athena also has a Patient Assistance Program, which may pay a substantial portion of the cost of testing for patients who qualify. (To qualify, a patient must submit tax returns and other financial records.) For more information, contact: 

Athena Diagnostics,Inc

Four Biotech Park

377 Plantation Street

Worcester, MA 01605

1-800-394-4493

www.athenadiagnostics.com