Dermatomyositis - Causes

Causes

The cause is unknown, but it may result from either a viral infection or an autoimmune reaction. In the latter case it is a systemic autoimmune disease. Many people diagnosed with dermatomyositis were previously diagnosed with infectious mononucleosis and Epstein-Barr virus. Some cases of dermatomyositis actually "overlap" (i.e. co-exist with or are part of a spectrum that includes) other autoimmune diseases such as Sjögren's syndrome, lupus, scleroderma, or vasculitis. Because of the link between dermatomyositis and autoimmune disease, doctors and patients suspecting dermatomyositis may find it helpful to run an ANA - antinuclear antibody - test, which in cases of a lupus-like nature may be positive (usually from 1:160 to 1:640, with normal ranges at 1:40 and below).

Several cases of polymyositis and dermatomyositis were reported as being triggered by the use of various statin drugs used to control blood cholesterol. Muscle biopsies of these patients showed rhabdomyolysis, and degeneration and regeneration of muscle tissue.

High blood levels of creatine kinase (CPK) showed greater than 5 times the normal levels also supporting the rhabdomyolysis findings. CPK is an enzyme found mainly in heart, brain, and skeletal muscle that tends to rise when inflammation occurs during normal exercise. When these levels rise in excess of the normal level (less than 200), and become more than five times higher, severe cell damage to the muscles, brain, and heart ensue. The higher the CPK, the greater the cellular damage done. Extremely high levels of CPK cause rhabdomyolysis to these muscles and organs. Without treatment, kidney damage occurs and death in the more severe cases. Confirmed polymyositis with the skin signs is known as dermatomyositis.

Some cases of dermatomyositis are a paraneoplastic phenomenon, indicating the presence of cancer. In cases involving cancer, the cancer is usually pre-existent, with removal of the cancer resulting in remission of the dermatomyositis. The onset of a rash in patients with pre-existing myositis requires investigation of the neoplastic possibility.

In his 1988 article, Clinical pathologic correlations of Lyme disease by stage, noted Lyme disease researcher Dr. Alan Steere observed, " the perivascular lymphoid infiltrate in clinical myositis does not differ from that seen in polymyositis or dermatomyositis. All of these histologic derangements suggest immunologic damage in response to persistence of the spirochete, however few in number."