Polymyositis

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Overview
Polymyositis is a type of inflammatory myopathy, related to dermatomyositis and inclusion body myositis. Polymyositis means 'many muscle inflammation'.

Polymyositis is one of a group of muscle diseases known as the inflammatory myopathies, which are characterized by chronic muscle inflammation accompanied by muscle weakness. Polymyositis affects skeletal muscles (those involved with making movement) on both sides of the body. It is rarely seen in persons under age 18; most cases are in adults between the ages of 31 and 60. Slow, but progressive muscle weakness starts in the proximal muscles (muscles closest to the trunk of the body) which eventually leads to difficulties climbing stairs, rising from a sitting position, lifting objects, or reaching overhead. People with polymyositis may also experience arthritis, shortness of breath, difficulty swallowing and speaking, and heart arrhythmias. In some cases of polymyositis, distal muscles (muscles further away from the trunk of the body, such as those in the forearms and around the ankles and wrists) may be affected as the disease progresses. Polymyositis may be associated with collagen-vascular or autoimmune diseases, such as lupus. Polymyositis may also be associated with infectious disorders, such as HIV-AIDS.

Polymyositis tends to become evident in adulthood, presenting with bilateral proximal muscle weakness, often noted in the upper legs due to early fatigue while walking. Sometimes the weakness presents itself by the person being unable to rise from a seated position without help, or inability to raise their arms above their head. The weakness is generally progressive, accompanied by lymphocytic inflammation (mainly cytotoxic T8 lymphocytes). The cause is unknown, but seems to be related to autoimmune factors, genetics, and perhaps viruses. In rare cases, the cause is known to be infectious, associated with the pathogens that cause Lyme disease, toxoplasmosis, and others.

Polymyositis, like dermatomyositis, strikes females with greater frequency than males. The skin involvement of dermatomyositis is absent in polymyositis.

Diagnosis
Diagnosis is fourfold, including elevation of creatine kinase, signs and symptoms, electromyograph (EMG) alteration, and a positive muscle biopsy. Treatment generally involves glucocorticoids, especially prednisone. At present, a number of studies are underway to determine whether patients diagnosed with polymyositis will benefit from newer drugs inhibiting the biologic effects of TNF alpha, such as Infliximab ("Remicade").

Sporadic inclusion body myositis (sIBM): IBM is often confused with (misdiagnosed as) polymyositis and polymyositis that does not respond to treatment is likely IBM. sIBM comes on over months to years, polymyositis comes on over weeks to months. It appears that sIBM and polymyositis share some common features, especially the initial sequence of immune system activation, however, polymyositis does not display the subsequent muscle degeneration and protein abnormalities as seen in IBM. As well, polymyositis tends to respond well to treatments, IBM does not. IBM and polymyositis apparently involve different disease mechanisms than are seen in dermatomyositis.

Treatment
There is no cure for polymyositis, but the symptoms can be treated. Options include medication, physical therapy, exercise, heat therapy (including microwave and ultrasound), orthotics and assisted devices, and rest.

The standard treatment for polymyositis is a corticosteroid drug, given either in pill form or intravenously. Immunosuppressant drugs, such as azathioprine and methotrexate, may reduce inflammation in people who do not respond well to prednisone.

Periodic treatment using intravenous immunoglobulin can also improve recovery.

Other immunosuppressive agents used to treat the inflammation associated with polymyositis include cyclosporine A, cyclophosphamide, and tacrolimus.

Physical therapy is usually recommended to prevent muscle atrophy and to regain muscle strength and range of motion.

Prognosis
The prognosis for polymyositis varies. Most people respond fairly well to therapy, but some have a more severe disease that does not respond adequately to therapies and are left with significant disability.

In rare cases individuals with severe and progressive muscle weakness will develop respiratory failure or pneumonia. Difficulty swallowing may cause weight loss and malnutrition.