Autoimmune myositis

[Couch Potatoe]

Autoimmune myositis causes inflammation and weakness in the muscles (polymyositis) or in the skin and muscles (dermatomyositis).

Muscle damage may cause muscle pain and muscle weakness may cause difficulty lifting the arms above the shoulders, climbing stairs, or arising from a sitting position.
Doctors check muscle enzymes in the blood and may test electrical activity of muscles, do magnetic resonance imaging on muscles, and examine a piece of muscle tissue.
Corticosteroids, immunosuppressive drugs, immune globulin , or a combination is usually helpful.

(See also Overview of Autoimmune Disorders of Connective Tissue.)
These disorders result in muscle inflammation (myositis), disabling muscle weakness, and occasionally tenderness. The weakness typically occurs in the shoulders and hips but can affect muscles symmetrically throughout the body.
Autoimmune myositis usually occurs in adults aged 40 to 60 or in children aged 5 to 15 years. Women are twice as likely as men to develop it. Black people are 3 to 4 times more likely to develop it than white people. In adults, these disorders may occur alone or as part of other connective tissue disorders, such as mixed connective tissue disease, systemic lupus erythematosus, or systemic sclerosis.
The cause of autoimmune myositis is unknown. Viruses may play a role, and cancer may occasionally trigger this disorder. The disorder can run in families.
There are four types of autoimmune myositis:

Polymyositis
Dermatomyositis
Necrotizing immune-mediated myopathies
Inclusion body myositis

Dermatomyositis usually causes skin changes that do not occur in polymyositis, which helps doctors differentiate the two disorders. Biopsy samples of muscle also look different under the microscope.
Necrotizing immune-mediated myopathies are disorders that kill muscle cells (myocytes) and do not damage tissue other than the muscles.
Inclusion body myositis is a separate disorder that has symptoms similar to chronic polymyositis of unknown cause. However, this disorder develops in older people, frequently involves other muscles (for example, hand and foot muscles) often with muscle wasting, progresses slower, and does not respond to therapy. Also, the muscle tissue has a different appearance under the microscope.