We report a case of carpal tunnel syndrome caused by palmaris profunda. Palmaris profunda is an anatomical variation of palmaris longus, which runs beneath the transverse carpal ligament and inserts palmar aponeurosis. Only six clinical cases with carpal tunnel syndrome caused by palmaris profunda have been reported in English medical literatures.
A 58-year-old man had numbness in the median nerve distribution of his left hand for three years. He visited our hospital because of exacerbation of numbness and development of the thenar muscle atrophy. Intraoperatively, palmaris profunda tendon was found in the carpal tunnel and median nerve was compressed under this tendon. Section of the transverse carpal ligament and excision of this tendon were performed. Complete relief of numbness and recovery of thenar muscle atrophy were achieved after surgery.