Charcot-Marie-Tooth disease (CMT) is the name given to a group of heritable conditions associated with progressive degeneration of the peripheral nerves. Peripheral nerves are those that carry sensory information from the body to the brain, and allow the brain to send nerve signals to muscles for movement.
CMT patients commonly experience difficulty walking due to loss of sensation and muscle strength in the feet and legs. Some may also develop difficulties with hearing sounds well, or hearing loss.
What causes hearing loss in CMT?
To perceive sound, vibrations are detected in the inner ear and converted to a nerve signal, sent by cochlear nerves to the brain to be interpreted. CMT can damage cochlear nerves, either through the degradation of the nerve fibers themselves or of the protein coat, called the myelin sheath, that protects these fibers.
This damage reduces a patient’s ability to hear, and usually occurs in both ears. Hearing loss can range from mild to severe in CMT, and patients usually have difficulty hearing mid- and high-frequency sounds.
How common is hearing loss in CMT?
There are different types of CMT, all caused by different genetic mutations. The symptoms and inheritance pattern of each type is different. Around 15 percent of patients with CMT type 1 experience hearing loss, while this percentage is higher — 30 percent — among those with CMT type 1B and CMT type 4. Some people with X-linked CMT and CMT type 2 may also have hearing loss.
A study published in Scientific Reports measured hearing loss in patients with CMT type 1, and found that these people often had “hidden hearing loss” — their ability to hear and to follow conversations appeared normal in quiet backgrounds, but was impaired in noisy environments.
Treatment of hearing loss
There are currently no treatments available to prevent or slow the progression of hearing loss in CMT patients. However, hearing aids can be of use to them, especially newer “programmable” ones, which can selectively amplify sound in environments with high background noise such as can occur at social gatherings, in cafeterias or classrooms, or on public transport.
Hearing loss in CMT patients may be present from infancy and worsen with disease progression. Late in life, some patients may lose the ability to hear.
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