Hypertrophied reverse palmaris longus muscle: a rare cause of carpal tunnel syndrome

Abstract

Carpal tunnel syndrome (CTS) is usually secondary to compression or irritation of the median nerve in the fibro-osseous canal formed by the flexor retinaculum (transverse carpal ligament) and the carpal bones. The prevalence of CTS in the general population is about 7 to 19%. Several causes both local and systemic have been described, but CTS due to aberrant musculature are rare. Here we report a case of a middle-aged female with paresthesia of the hand and a positive Phalen’s test with nerve conduction study of the median nerve showing sensorimotor neuropathy. The patient underwent surgery for open CTS release where we found a hypertrophied reverse palmaris longus muscle attached to the palmar aponeurosis which was excised along with its proximal tendon. On post-operative follow up all the symptoms of CTS were completely resolved. Muscle abnormalities concern three muscles: the palmaris longus, the flexor digitorum superficialis of index, and the lumbricals. These muscles can be hypertrophied, bifid, duplicated, digastric, inverted or have an abnormal insertion, thus creating a mechanical restriction of the carpal tunnel. Surgical resection of abnormal muscle provides excellent functional recovery.