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.