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Myositis (dermatomyositis & polymyositis)
Autoimmune inflammation of the muscles that causes weakness around the hips and shoulders — sometimes with a rash or lung involvement.
What is myositis?
Myositis means inflammation of the muscles. In rheumatology it usually refers to the idiopathic inflammatory myopathies — autoimmune conditions in which the immune system attacks muscle, and sometimes the skin, lungs and joints. The main types are dermatomyositis (with a rash), polymyositis, antisynthetase syndrome, immune-mediated necrotising myopathy and inclusion body myositis.
Symptoms to recognise
- Weakness of the thighs, hips, shoulders and upper arms — trouble climbing stairs, rising from a chair, lifting the arms, combing hair
- A violet or reddish rash on the eyelids, knuckles, chest or back (dermatomyositis)
- Rough, cracked skin on the fingers ("mechanic's hands")
- Difficulty swallowing or a change in voice
- Breathlessness or a dry cough — lung involvement needs prompt assessment
- Joint pain, Raynaud's, fatigue
Muscle weakness is the key feature — muscle aches alone, without weakness, are rarely myositis.
How it is diagnosed
- CK (creatine kinase) and other muscle enzymes
- Myositis antibody panel — helps define the type and guides treatment
- MRI of the thigh muscles to show inflammation and guide biopsy
- EMG and muscle biopsy where needed
- Lung assessment — CT scan and breathing tests
- Cancer screening in adults with dermatomyositis, because of a known association
How it is treated
- Steroids to bring inflammation under control
- Steroid-sparing medicines: methotrexate, azathioprine, mycophenolate
- IVIG or rituximab for severe or resistant disease
- Physiotherapy and graded exercise — an essential part of recovery
- Sun protection for dermatomyositis rashes
Muscle strength usually recovers over months. Some statin-related forms improve on stopping the statin; others need full immunosuppressive treatment.
Common questions
Is myositis the same as muscle pain?+
No. Myositis causes true weakness of muscles, usually around the hips and shoulders. Muscle aches without weakness have many other causes.
Can statins cause myositis?+
Statins commonly cause muscle aches, which settle on stopping. Rarely they trigger an autoimmune necrotising myopathy that persists after stopping and needs specialist treatment.
Will my strength come back?+
For most forms, yes — with treatment and physiotherapy strength improves over months. Inclusion body myositis is different and progresses slowly despite treatment.