Short, plain-language answers to the questions we hear most often. For anything specific to you, your care team is the best guide.
Myositis, or idiopathic inflammatory myopathy, is a group of rare autoimmune diseases in which the immune system attacks the muscles. This leads to inflammation, muscle weakness, and sometimes changes in the skin, lungs, joints, or swallowing. It can affect both adults and children.
The most common symptom is muscle weakness, often in the hips, thighs, shoulders, and upper arms, which can make climbing stairs, lifting, or rising from a chair harder. Some people also notice muscle aching, tiredness, a skin rash, trouble swallowing, or shortness of breath. Symptoms usually build up over weeks to months.
The exact cause is not fully understood. In most types, the immune system mistakenly attacks muscle tissue. Some cases are linked to specific antibodies, and in a small number of adults dermatomyositis is associated with an underlying cancer, which is why screening is sometimes done. Myositis is not contagious and cannot be passed from person to person.
The main types are dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, inclusion body myositis, and antisynthetase syndrome, along with juvenile myositis in children. They differ in their symptoms, the antibodies involved, and how they respond to treatment. Understanding myositis →
Myositis is usually not inherited, and most people have no family history of it. You cannot pass it on the way you would a simple genetic condition. Some genetic factors may slightly raise the risk of inclusion body myositis, but that does not mean it runs directly in families.
Myositis is rare. Estimates vary, but inflammatory myopathies affect only a few people in every 100,000. Because it is uncommon, care is best guided by a team that sees it often.
Myositis is a serious condition, but with the right treatment many people do well and stay active. Some forms can affect the lungs, heart, or swallowing, which is why regular monitoring is part of care. Outcomes vary by type, and a specialist team can help manage both the disease and any complications.
Yes. Some types, particularly antisynthetase syndrome, can cause inflammation and scarring in the lungs known as interstitial lung disease. This is why breathing tests, and sometimes a CT scan of the chest, are part of care. Tell your team about any new cough or shortness of breath.
Diagnosis usually combines your history and physical examination, blood tests (including muscle enzymes and a myositis-antibody panel), and further tests such as an EMG, an MRI, or a muscle biopsy. Together these confirm the diagnosis and the type of myositis. Tests and procedures →
A common blood test measures creatine kinase (CK), an enzyme that rises when muscle is inflamed or damaged. A myositis-antibody panel looks for specific antibodies that help identify the type of myositis and predict which organs may be involved.
An EMG is usually uncomfortable rather than painful, and the discomfort is brief. It involves small electrical pulses on the skin and a fine needle placed into a few muscles. Most people tolerate it well and can drive themselves home afterward. Read the EMG guide →
Most types of myositis can be controlled with treatment, even if they are not permanently cured, and many people improve and regain strength. Inclusion body myositis is the exception, as it does not respond well to immune-suppressing medicines and is managed mainly with rehabilitation and staying active.
Treatment often starts with a corticosteroid such as prednisone, usually alongside a steroid-sparing medicine that lowers the immune attack. Some people also receive intravenous immunoglobulin (IVIG) or other targeted treatments. The right combination depends on the type of myositis. Medication guides →
Yes. It was once thought that exercise might worsen myositis, but we now know that guided exercise is helpful and important. A physiotherapist can design a safe program to build strength and keep you moving. Exercise and myositis →
There is no single myositis diet, but eating well supports your muscles, bones, and general health, especially while taking steroids. Our patient nutrition guides, including a vegetarian option, offer practical starting points. Diet and nutrition →
Myositis is usually cared for by a rheumatologist, a neurologist, or both, often together with a physiotherapist. The Toronto Myositis Centre at St. Michael's Hospital brings these specialists into one clinic, so people across Ontario can be assessed and treated by a team experienced in inflammatory muscle disease. How referral works →
This page is for general information, not medical advice. Myositis affects everyone differently, so always discuss your own situation with your care team.