Anomalous Muscles, A Rare Cause of Carpal Tunnel Syndrome: A Case Report

Abstract

Carpal tunnel syndrome (CTS) is secondary to compression or irritation of the median nerve in the osteofibrous canal formed by the flexor retinaculum and the carpal bones. The prevalence rate in the general population is between 7 and 19%. Several local and systemic causes have been described, but muscular abnormalities have rarely been reported in the literature. We report a clinical case that we encountered during a carpal tunnel release in our practice. A 62-year-old right handed, female patient, presented to the orthopedic consultation with paraesthesia of the first three fingers. The electromyogram showed motor deficiency in loaf muscles therefore, allowed the diagnosis of CTS. The patient underwent surgery for CTS release. There was anomalous muscles attached to the palmaris longus, which was excised and the canal left open. At six month, follow up all the symptoms of CTS completely resolved. Muscular abnormalities are found mainly in manual workers. Those 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. It is relevant to think about of a muscular cause in clinical atypical presentation of carpal tunnel syndrome and MRI investigation. Complete and successful surgical resection of abnormal muscle provides excellent functional recovery.