Extensor indicis proprius syndrome secondary to an anomalous extensor indicis proprius muscle belly

The complaint of dorsal hand pain is common among patients seen in a primary care practice. The differential diagnosis includes tenosynovial disease, ganglion, trauma, and soft-tissue tumors. Rarely is an anomalous muscle an etiologic factor. Reported here is an anomalous indicis proprius muscle that was manifested as a painful dorsal hand mass. Also discussed are the anatomic variations of the extensor indicis proprius syndrome.