People with myotonic dystrophy DM1 have an increased frequency of pilomatrixoma, a type of benign skin tumor. This type of tumor is rare in the general population but fairly common in people with myotonic dystrophy DM1. (No association between pilomatrixomas and DM2 has been reported).
Pilomatrixomas often occur around the head or neck and feel like firm lumps just beneath the surface of the skin. These tumors are benign and can be cured by surgical removal. Some researchers have suggested that DM1 may also be associated with an increased frequency of other types of tumors, such as tumors of the parathyroid, pituitary, or thymus glands. However, at this point there is no clear evidence to support this idea.