Several tests are usually done to diagnose Charcot-Marie-Tooth disease, a group of inherited peripheral neuropathies — disorders that affect the nerves that control sensation, movement, and motor coordination. In rare cases, those assessments can be inconclusive.
There are different types of CMT, caused by different genetic mutations. These mutations either affect the nerve cells themselves or the myelin sheath, the insulating layer protecting nerve fibers that is critical for proper transmission of nerve signals. Ultimately, such mutations impact the peripheral nerves, which are located outside the brain and spinal cord and control movement and coordination of the arms and legs, as well as sensation.
The most common tests for diagnosing CMT include nerve conduction studies or electromyography — which check how well electrical signals are being transmitted by the nerves to the muscles — and genetic testing, used to check for mutations known to cause the disorder. In a nerve biopsy, a small piece of nerve tissue is tested.
What is a nerve biopsy?
A nerve biopsy involves the surgical removal of a small piece of peripheral nerve tissue — usually taken from one leg — to be examined in a laboratory.
For the procedure, a small incision is made under a local anesthetic to remove the piece of the nerve. The biopsy is generally taken from the calf region of the lower leg.
How does a nerve biopsy diagnose CMT?
Particular abnormalities in the peripheral nerves — and specific to disease type — can be evident in CMT patients and visible under a microscope in tissue removed by biopsy.
For example, CMT type 1 can cause repeated demyelination and remyelination, or the loss and reformation of the protective myelin sheath. This is associated with nerve fibers being surrounded by “onion bulb”-shaped clumps of Schwann cells, which form myelin in the peripheral nervous system. Some CMT type 1 patients also may have “tomacula,” or swellings in the myelin sheath.
CMT type 2 is expected to lead to changes common to Wallerian degradation, the set of cellular and molecular events that result in nerve fiber degeneration after sustaining damage.
In different types of CMT, immune cells known as lymphocytes and macrophages may indicate the presence of inflammation.
Risks associated with nerve biopsy
A nerve biopsy carries a very low risk of causing nerve damage. After it is performed, a small area may be permanently numb. Potential discomfort and infection are other possible risks. There also is a risk of the patient having an allergic reaction to the anesthetic.
Last updated: Oct. 20, 2021
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