ConditionBones, joints & muscles
Myositis: Understanding Inflammatory Muscle Diseases
Myositis means inflammation of the muscles. It causes muscle weakness, usually in the shoulders, hips and thighs, and sometimes pain and tiredness. The most common cause is a short-lived viral infection such as flu. Less often it is a chronic autoimmune disease, an idiopathic inflammatory myopathy, such as dermatomyositis, polymyositis, inclusion body myositis or necrotizing myopathy. These need prompt diagnosis with blood tests, EMG, MRI and a muscle biopsy, and are treated with steroids, immunosuppressants and exercise.
Also called: Inflammatory myopathy, idiopathic inflammatory myopathies, muscle inflammation
At a glance
- What it is
- Inflammation of skeletal muscle causing weakness, sometimes with pain.
- Most common
- Short-term viral myositis, especially after flu in children.
- Chronic types
- Dermatomyositis, polymyositis, inclusion body myositis, immune-mediated necrotizing myopathy, antisynthetase syndrome.
- Diagnosis
- CK blood test, autoantibodies, EMG, MRI and muscle biopsy.
- Treatment
- Corticosteroids plus steroid-sparing immunosuppressants, IVIG for some, and physical therapy.
When to get help
Call 911 or go to the ER
- Difficulty breathing, or choking and coughing when swallowing, with muscle weakness
- Dark brown or cola-colored urine with severe muscle pain and weakness (possible rhabdomyolysis)
- A child with severe calf pain after flu who refuses to walk and has dark urine
See a doctor within a day or two
- Rapidly progressive weakness: trouble climbing stairs, rising from a chair or lifting arms over the head over days to weeks
- Weakness with a new cough or breathlessness (possible lung involvement)
- Muscle weakness and pain after starting a statin that does not settle after stopping it
Book a routine appointment
- Gradual difficulty with stairs, standing up or reaching overhead
- A purplish rash on the eyelids or red bumps over the knuckles
- Frequent falls, or weakness in the grip or thigh muscles in an older adult
Types of myositis
| Type | Who | Key features |
|---|---|---|
| Viral myositis | Often children after flu; any age | Calf pain and tenderness, toe-walking; resolves in days |
| Dermatomyositis | Children and adults | Weakness plus a distinctive rash; linked to cancer in some adults |
| Polymyositis | Adults | Weakness without rash; less common than once thought |
| Inclusion body myositis | Usually over 50, more in men | Slow weakness of thigh muscles and finger grip; often asymmetric; poor response to immunosuppression |
| Immune-mediated necrotizing myopathy | Adults | Rapid, severe weakness, very high CK; can be triggered by statins (anti-HMGCR antibodies) |
| Antisynthetase syndrome | Adults | Myositis, interstitial lung disease, arthritis, "mechanic's hands" |
| Overlap myositis | Adults | Myositis with lupus, scleroderma or other autoimmune diseases |
Symptoms
Muscles
- weakness, usually symmetrical, of the shoulders, upper arms, hips and thighs
- difficulty climbing stairs, getting up from a chair, lifting the arms above the head or brushing hair
- in inclusion body myositis, weak grip and quadriceps
- muscle aches and tenderness in some, but often painless
- fatigue
Skin (dermatomyositis)
- purple-red discoloration of the upper eyelids (heliotrope rash), often with swelling
- red, scaly bumps over the knuckles (Gottron's papules)
- a red rash on the chest (V-sign) or upper back (shawl sign)
- rough, cracked skin on the hands ("mechanic's hands")
- calcium deposits under the skin in children
Other organs
- swallowing problems (difficulty swallowing) and aspiration
- lung involvement: interstitial lung disease, causing cough and breathlessness
- heart involvement: rhythm problems or heart muscle inflammation
- joint pain and Raynaud's phenomenon
Causes
- viral infections: influenza, COVID-19, enteroviruses and others
- autoimmune processes in idiopathic inflammatory myopathies
- medicines: statins (most statin muscle aches are not myositis; rarely they trigger an autoimmune necrotizing myopathy), some immune checkpoint cancer drugs, and others
- cancer: dermatomyositis in adults is associated with an increased risk of cancer, especially in the first few years
Diagnosis
- CK (creatine kinase) and other muscle enzymes: often raised, sometimes very high
- myositis-specific and associated autoantibodies such as anti-Jo-1, anti-Mi-2, anti-HMGCR and anti-SRP
- EMG (electromyography): shows muscle-related rather than nerve-related weakness
- MRI of the thighs: shows inflamed muscle and guides biopsy
- muscle biopsy: confirms the type
- lung tests: breathing tests and chest CT
- heart tests: ECG and echocardiogram
- cancer screening in adults with dermatomyositis and some other types
Muscle weakness has many other causes, including thyroid disease, electrolyte imbalance, muscular dystrophies and nerve disease, which doctors exclude.
Treatment
Viral myositis
Rest, fluids and pain relief such as acetaminophen (paracetamol) or ibuprofen at label doses. Symptoms usually resolve within a week. Watch for dark urine, which can signal rhabdomyolysis.
Autoimmune myositis
- corticosteroids (such as prednisone) as initial treatment
- steroid-sparing immunosuppressants: methotrexate, azathioprine, mycophenolate
- intravenous immunoglobulin (IVIG): approved for dermatomyositis and used for severe or resistant disease and swallowing problems
- rituximab and other therapies for refractory disease
- treatment for lung disease, skin disease (sun protection, hydroxychloroquine) and calcinosis
- stopping statins if they triggered necrotizing myopathy
Inclusion body myositis does not respond well to these medicines; care focuses on exercise, mobility aids and managing swallowing.
Exercise and therapy
Supervised exercise and physical therapy are safe and help maintain strength and function in all types. Speech therapy helps swallowing problems.
Outlook
Viral myositis resolves completely. Many people with dermatomyositis and polymyositis improve substantially with treatment, though some need long-term therapy, and relapses can occur. Inclusion body myositis progresses slowly over years. Lung involvement and cancer association affect prognosis, so regular follow-up matters.
Frequently asked questions
What is myositis?
Myositis is inflammation of the muscles, causing weakness and sometimes pain. It can be a short-lived complication of a viral infection or a chronic autoimmune disease such as dermatomyositis, polymyositis or inclusion body myositis.
What are the first symptoms of myositis?
Early symptoms are usually difficulty climbing stairs, rising from a chair or lifting your arms, along with tiredness. Dermatomyositis also causes a purplish eyelid rash and red bumps on the knuckles. Viral myositis in children causes calf pain and difficulty walking after flu.
How is myositis diagnosed?
Doctors use blood tests for muscle enzymes (CK) and specific antibodies, EMG, MRI of the muscles and often a muscle biopsy. Lung and heart tests and cancer screening may also be done.
Can myositis be cured?
Viral myositis resolves on its own. Autoimmune myositis is usually a long-term condition, but treatment with steroids, immunosuppressants and exercise brings many people into remission or good control. Inclusion body myositis responds poorly to medicines.
Sources
This guide was written from current patient and clinical guidance, including:
- The Myositis Association: Types of myositis
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS): Myositis
- National Institute of Neurological Disorders and Stroke: Inflammatory myopathies
- American College of Rheumatology: Myositis
- EULAR/ACR classification criteria for idiopathic inflammatory myopathies