Medical Info: Polymyositis

Polymyositis is a disease of muscle featuring inflammation of the muscle fibers. The cause of the disease is not known. It begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles. The muscles affected are mostly those closest to the trunk or torso. This results in weakness which can be severe. It is a chronic illness with periods of increased symptoms, called flares or relapses, and decreased symptoms, known as remissions.

Polymyositis is slightly more common in females. It affects all age groups, although its onset is most common in middle childhood and in the twenties. Polymyositis occurs throughout the world. Polymyositis can be associated with skin rash and is then referred to as "dermatomyositis." It also can affect other areas of the body and is, therefore, a systemic illness. Occasionally, it is associated with cancer, or with other diseases of connective tissue (see systemic lupus erythematosus, scleroderma and rheumatoid arthritis).


Medical info:

Causes:

To date, no cause of polymyositis has been isolated by scientific researchers. There are indicators of heredity (genetic) susceptibility that can be found in some patients. There is indirect evidence of infection by a virus that has yet to be identified in a form of polymyositis that is particularly resistant to treatment, called inclusion body myositis. This form of polymyositis is diagnosed by the pathologist, a physician specialist who interprets the microscope findings of muscle tissue. The muscle tissue in this form of polymyositis displays clear areas within the muscle cells (called vacuoles) when viewed under the magnification of a microscope.

Aside from diseases with which polymyositis can be associated (as mentioned above), many other diseases and conditions can mimic polymyositis. These include nerve-muscle diseases (such as muscular dystrophies), drug toxins (such as alcohol, cocaine, steroids, colchicine, hydroxychloroquine, and cholesterol lowering drugs), metabolic disorders (where muscle cells are unable to process chemicals normally), hormone disorders (such as abnormal thyroid), calcium, and magnesium conditions), and infectious diseases (such as influenza virus, AIDS, streptococcus and Lyme bacteria, pork tapeworm and schistosomiasis).


Symptoms:

Weakness of muscles is the most common symptom of polymyositis. The muscles involved usually are those that are closest to the trunk of the body. The onset can be gradual or rapid. This results in varying degrees of loss of muscle power and atrophy. The loss of strength can be noticed as difficulty getting up from chairs, climbing stairs or lifting above the shoulders. Trouble with swallowing and weakness lifting the head from the pillow can occur. Occasionally, the muscles ache and are tender to the touch (25% of patients).

Patients can also feel fatigue, a general feeling of discomfort and have weight loss and/or low-grade fever.

With skin involvement (dermatomyositis), the eyes can be surrounded by a violet discoloration with swelling. There can be scaly reddish discoloration over the knuckles, elbows and knees (Gottron's sign). There can also be reddish rash on the face, neck and upper chest. Hard lumps of calcium deposits can develop in the fatty layer of the skin, most commonly in childhood dermatomyositis.

Heart and lung involvement can lead to irregular heart rhythm, heart failure, and shortness of breath.

Because polymyositis can present in combination with other illnesses (see related articles on systemic lupus erythematosus, scleroderma and rheumatoid arthritis), it can also have overlap features with them. These illnesses are discussed elsewhere.

Both polymyositis and dermatomyositis can sometimes be associated with cancers, including lymphoma, breast cancer, lung cancer, ovarian cancer, and colon cancer. The cancer risk is reported to be much greater with dermatomyositis than polymyositis.