Familial Carpal Tunnel Syndrome (CTS)

At a glance

A familial disorder of constrictive median neuropathy caused by enlarged tendons and/or ligaments in the wrist.

Synonyms

Thenar Amyotrophy of Carpal Origin; Constrictive Median Neuropathy.

Incidence

The incidence and prevalence for this medical condition remains unknown. However, it is believed to be underdiagnosed as a familial condition and for this reason must be highly prevalent.

Genetic inheritance

Autosomal dominant. A high degree of penetrance within affected families has been described.

Familial transthyretin (TTR) amyloid polyneuropathy (also called hereditary TTR amyloidosis, or TTR-type of familial amyloid polyneuropathy) is a rare systemic disorder that can present with progressive, sensory and motor neuropathy and restrictive cardiomyopathy (transthyretin cardiomyopathy), or less frequently as cerebral amyloid angiopathy. CTS is the presenting symptom in about one-third of these patients, often with no other clinical manifestations occurring for about 5 years on average. The defect has been linked to mutations in the TTR (transthyretin from [transporter of thyroxine and retinol]; formerly thyroxine-binding prealbumin) gene, which has been mapped to chromosome 18q12.1. TTR protein is a systemic amyloid precursor and involved in different forms of amyloidosis that can accumulate in peripheral and autonomic nerves and in the heart. TTR protein aggregation is also found in senile systemic amyloidosis, a late onset disease that results in protein deposits in the heart, gut, and carpal tunnel.

Diagnosis

Early age of onset (usually third decade of life, but onset already in the first year of life is possible) of entrapment neuropathy. The progressive course most often needs surgical decompression. The clinical course is characteristic and includes paresthesia in the distribution of the median nerve with nocturnal aggravation of symptoms, and thenar atrophy and hand weakness in long-standing cases. Electromyography can be used to confirm the diagnosis. In isolated, bilateral, early onset CTS, the possibility of familial TTR amyloid polyneuropathy (although rare) should be kept in mind.

Clinical aspects

The sporadic and more common form of CTS occurs bilaterally in half of the cases, typically affects middle-aged women and rarely occurs before 20 years of age. In contrast, familial CTS is almost always bilateral, presents at a mean age of about 27 years, and in one-third of the patients even before the age of 20 years. Familial CTS is caused by marked, noninflammatory thickening of the transverse carpal ligaments (flexor retinaculum) and/or flexor tendon sheaths, or digital flexor tenosynovitis and leads to constrictive median neuropathy, associated with thenar atrophy and weakness of the hand. Severe vitamin B₆ deficit can be associated with CTS, and supplemental vitamin B₆ has improved the symptoms in some cases, even obviating surgery. The typical clinical manifestation can be reproduced three ways: volar wrist percussion (Tinel sign), sustained ...