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Carpal tunnel syndrome caused by an anomalous palmaris profundus tendon.

The carpal tunnel syndrome is the most common entrapment neuropathy in adults. Rarely, compression of the median nerve at the wrist may be caused by the presence of a tendon or muscle anomaly. Palmaris profundus, the tendon of which runs deep to the flexor retinaculum and inserts into the palmar aponeurosis, is an anomalous muscle arising from the fibrous tissue of the proximal portion of the forearm. As cited by Fatah (1984), it was first described by Frohse & Frankel in 1908. In an anatomical study of 1600 limbs, Riemann et al. (1944) found palmaris profundus in only 1 cadaver in which the associated absence of palmaris longus led to the conclusion that the former was an anatomical variant of the latter. Brones & Wilgis (1978) described 2 further examples of palmaris profundus. Dyreby & Engber (1982) reported a case of palmaris profundus causing the carpal tunnel syndrome in which the anomalous muscle was situated behind palmaris longus and, from its origin on the radius, passed through the flexor retinaculum. Fatah (1984) also described 2 cases of palmaris profundus associated with the carpal tunnel syndrome. In 1 of these cases a muscle bundle in the middle portion of the forearm was found when the dissection was extended proximally. Floyd & Burger (1990) published a case of bilateral carpal tunnel syndrome caused by bilateral palmaris profundus muscles coexisting with palmaris longus. We describe a further case in which tendons from both palmaris profundus and palmaris longus were present.