Myotonic dystrophy is associated with a modest reduction in the amount of immunoglobulin in the blood (hypogammaglobulinemia). The production of antibodies is normal, however the antibodies do not last as long in the circulation, hence the amount in the blood at any time is somewhat reduced. The myotonic dystrophy-associated reduction of immunoglobulin appears to be well tolerated. So far there is no clear evidence that alteration is associated with an increased frequency of infection.
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.