Short, plain-language answers to the questions we hear most often. For anything specific to you, your care team is the best guide.
Myositis simply means muscle inflammation. It is not a specific condition. A more specific term is "Idiopathic Inflammatory Myopathies" (IIM). This refers to a group of rare autoimmune diseases in which the immune system attacks the muscles. This leads to inflammation and muscle weakness. These diseases can also affect other areas of the body including the skin, lungs, joints, or swallowing. There are several different sub-types of these conditions and they 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 sub-types, the immune system mistakenly attacks muscle tissue. Some cases are linked to specific antibodies, different types of medications, and in a small number of adults it is associated with an underlying cancer. These autoimmune muscle conditions are not contagious and cannot be passed from person to person.
The main subtypes of autoimmune myositis are dermatomyositis, immune-mediated necrotising myositis, antisynthetase syndrome, and overlap connective tissue disease myositis, as well as juvenile myositis in children. They differ in their symptoms, antibodies involved, and how they respond to treatment. There are many other types of muscle conditions that are unrelated to autoimmune disease but can lead to similar symptoms of progressive weakness. These include degenerative, genetic, and neurological conditions, such as inclusion body myositis, which can sometimes be confused with the autoimmune types. Our team can help distinguish between these causes. Understanding myositis →
These are rare conditions. Estimates vary, but IIM affect only a few people in every 100,000. Because it is uncommon, care is best guided by a team that sees it often.
These are generally serious conditions, but with the right treatment many people do well and stay active. Severity can vary greatly from one person to another, even within the same myositis sub-type. Some forms can affect the lungs, heart, or swallowing, which can lead to serious complications. This highlights the need for regular monitoring as part of care. Outcomes vary by type, and generic information you may find online might not capture the variability and spectrum of disease manifestations.
No. Most people with these conditions never develop cancer. Some forms, mainly dermatomyositis in adults and certain antibodies, carry a higher risk that a cancer is found, particularly in the first few years after myositis diagnosis. That is why your team screens carefully in the first years after diagnosis, to try and identify an underlying cancer as early as possible. How antibodies guide screening →
Yes. Some types, particularly antisynthetase syndrome, can cause inflammation and scarring in the lungs known as interstitial lung disease (ILD). 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 can help predict which organs may be involved. Our new guides cover this in detail: blood tests and the antibody panel.
Yes. While this is less common, in some myositis subtypes normal or only mildly raised muscle enzymes could be seen, and not all people test positive for one of the myositis antibodies. Therefore normal bloodwork does not always end the diagnostic journey. Additional testing might be needed, including considering alternative causes of your symptoms. Read the blood tests guide →
It does not mean something specific. You can still have the condition with a weak positive result. At the same time, false positives are not unheard of on the myositis panel. It is important to understand that these antibodies are not diagnostic by themselves. Some can also be found in healthy people. Your specialist reads the result in the context of your whole picture rather than just relying on it or on how positive it is. Read the antibody panel guide →
An EMG could be mildly uncomfortable rather than painful, but the discomfort is typically brief. It involves small electrical pulses on the skin and a fine needle placed into a few muscles. Most people tolerate it well with no adverse effect. Read the EMG guide →
Untreated inflammation keeps damaging muscle, and weakness that lasts a long time becomes harder to reverse. Myositis can also involve the lungs, the swallowing muscles, and the heart, and finding that early changes how well treatment works. This is why we treat promptly rather than watching and waiting. With treatment, most people improve, and many return to the activities that matter to them.
These autoimmune muscle conditions are not curable. However, we have effective medications to control them and achieve a state of remission where the disease is not active. Many people improve and regain strength. This is different when compared to other types of muscle conditions such as inclusion body myositis, which does not respond to immune-suppressing medicines.
Treatment often starts with a corticosteroid such as prednisone, usually alongside a steroid-sparing medicine that lowers the immune attack on the muscle and other affected areas. 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 autoimmune-related 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 patients 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.