Familial amyloid polyneuropathy (FAP) results from a mutation in the transthyretin (TTR) gene that causes abnormal TTR protein deposits, called amyloids, to accumulate in the peripheral nervous system, and other tissues and organs.
The buildup of amyloids on the peripheral nerves impedes communication between the brain and the rest of the body, causing the peripheral neuropathy symptoms observed in FAP.
Carpal tunnel syndrome is one of the most commonly reported symptoms of peripheral neuropathy in FAP patients.
What is carpal tunnel syndrome
The carpal tunnel is a narrow passage of the wrist through which the median nerve, which originates at the base of the neck, passes into the hand. The median nerve is the main nerve in the hand and responsible for sensations in the thumb, index, middle and ring fingers. It also supports the muscles at the base of the thumb.
Carpal tunnel syndrome develops as the result of the compression of the median nerve. It causes symptoms such as numbness, pain, and tingling in the hand and arm, and gripping difficulties.
In FAP, the damage to the peripheral nerves caused by the buildup of amyloid deposits can cause median nerve compression, leading to these symptoms.
Diagnosis of carpal tunnel syndrome
To diagnose carpal tunnel syndrome, the doctor will first review the patient’s medical history. The little finger is not connected by the median nerve, so any symptoms associated with the pinky can help to rule out carpal tunnel syndrome.
Physical examination to test strength and sensation in the fingers and hand muscles will also be performed. Two common tests are the Tinel’s sign test and Phalen’s test or wrist flexion test. In Tinel’s test, the doctor taps the median nerve to see if it elicits symptoms of carpel tunnel syndrome, such as tingling in the fingers. In the Phalen’s test, he or she flexes the patient’s wrist back and forth. People with carpal tunnel syndrome will feel numbness and tingling in the fingers within 60 seconds of this test.
A doctor can also order specific tests to rule out other conditions than FAP as a possible cause of carpal tunnel syndrome. For example, a wrist MRI can help to rule out arthritis or a fracture.
Electromyography (EMG) and nerve conduction studies (NCS) will be performed to assess the level of median nerve function. EMG evaluates muscle activity and damage. NCS evaluates the ability of nerves to transmit messages.
Management
Resting the hand, and avoiding strenuous activities that trigger carpal tunnel syndrome can help to manage the condition.
Exercise to support the carpal tunnel, along with other treatments, can also help alleviate the symptoms of tingling and numbness. Physical and occupational therapy can help manage carpal tunnel syndrome symptoms and guide patients to readjust activities that trigger the condition.
Yoga has proven helpful in some instances.
Treatment
Wearing a splint or wrist brace to support the wrist, and using nonsteroidal anti-inflammatory medications such as aspirin or ibuprofen to alleviate pain can help patients with mild or moderate carpal tunnel syndrome.
Doctors may recommend corticosteroids injections in the wrist to relieve inflammation and swelling, which eases pressure on the median nerve. This can reduce carpal tunnel syndrome-associated pain.
Surgery is an option for patients with severe carpal tunnel syndrome. The doctor may either relieve the pressure on the median nerve endoscopically, with the guidance of ultrasound, or through open surgery.
In open surgery, an incision is made on the palm just above the wrist to visualize the median nerve, and necessary adjustments are made to decrease the pressure on it. Although the skin incision may heal within weeks, internal healing can take months. Some of the risks associated with this surgery include incision infection, scarring, incomplete release of pressure, or nerve injuries.
Endoscopic surgery is quicker, less painful, and heals faster than open surgery.
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