A rare heterotopic ossification, especially of the great toe. The term 'exostosis' is a misnomer since there is no continuity within the underlying bone. This lesion is unrelated to OSTEOCHONDROMA, which is a true exostosis with continuity to the underlying bone, and is more similar to MYOSITIS OSSIFICANS. This subungual lesion usually presents as a painful dorsomedial mass, often associated with elevation and ultimately ulceration of the nail plate and bed. Occurs most often in patients between 15 and 25 years of age. OMIM: 603656
