Myositis (Idiopathic Inflammatory Myopathy)

Myositis is a disease that makes your immune system attack your muscles. It causes chronic muscle inflammation. Eventually, the inflammation makes your muscles feel increasingly weak. It can also sometimes cause muscle pain.

These days, healthcare providers call myositis by a more accurate medical name, idiopathic inflammatory myopathy (IIM). Your provider may use either name, but they both refer to the same condition.

IIM is a form of myopathy. These are diseases that affect muscles that connect to your bones (skeletal muscles). Different types affect different muscle groups throughout your body.

Myositis usually affects the muscles you use to move, especially those in your:

• Arms and shoulders
• Thighs and hips
• Abdomen and spine (but this is less common)

You might experience muscle weakness in or near your esophagus and diaphragm.

Experts aren’t certain what causes IIM, and there’s no cure for it. Your healthcare provider will treat the symptoms you’re experiencing. They’ll also recommend exercises or stretches that can help your affected muscles between episodes.

Visit a healthcare provider if you feel weak, have trouble moving or notice new pain or skin rashes. Go to the emergency room if you have trouble breathing or swallowing.

Types of myositis

A healthcare provider will diagnose a type of idiopathic inflammatory myopathy based on the symptoms you have and which muscles are affected. There are a few different forms, including:

• Anti-synthetase syndrome: This condition causes inflammation in your muscles, joints and lungs. It usually leads to muscle weakness, especially in muscles close to the center of your body. You might have joint pain, breathing problems and skin changes on your hands.
• Immune-mediated necrotizing myopathy: This can happen when your immune system attacks your muscles. You’ll have severe muscle weakness, usually in your shoulders, hips, arms and legs. Symptoms often develop quickly and make it hard to do physical activities.
• Dermatomyositis: You’ll have symptoms that affect your skin along with your muscles. Dermatomyositis can be fatal if it’s not treated as soon as possible. Visit a healthcare provider right away if you think you may have it.
• Inclusion body myositis: This type affects your extremities (your hands and your legs below your knees). Inclusion body myositis can also weaken the muscles in your throat that help you swallow. It’s most common in people over 50.

Symptoms of myositis

Myositis symptoms include:

• Muscle weakness
• Joint or muscle pain
• Fatigue
• Swelling
• Trouble breathing or swallowing
• Arrhythmia (if the myositis affects your heart)
• A skin rash (if you have dermatomyositis)

During an episode of symptoms, you might have trouble moving or doing certain activities you usually can do. You might get tired faster, or feel like you can’t control your arms, hands or legs.

Different types of myositis have different symptoms. Your healthcare provider will tell you what to expect and which symptoms you’ll experience.

Myositis causes

Experts don’t know for sure what causes myositis. It can occur on its own. Sometimes, other health conditions trigger it.

Idiopathic inflammatory myopathy is an autoimmune disease. Autoimmune diseases are the result of your immune system accidentally attacking your body instead of protecting it. It’s unclear why your immune system does this. You’re more likely to develop myositis if you have other autoimmune diseases, including:

• Lupus
• Rheumatoid arthritis
• Scleroderma

You may develop myositis after you have a viral infection. Causes of viral myositis can include:

• The common cold
• Influenza (the flu)
• HIV
• COVID-19

How doctors diagnose this condition

A healthcare provider will diagnose myositis with a physical exam and tests. They’ll examine any symptoms you have and ask how it feels when you do certain movements or motions. You might need a few tests, including:

• Blood tests
• MRI
• EMG or nerve conduction velocity (NCV) test
• Muscle biopsy

How is myositis treated?

Your healthcare provider will treat the IIM symptoms to reduce their impact on your daily routine. Their goal will be to treat symptoms until the myositis goes into remission (when there’s little or no inflammation in your muscles). Typical treatments for myositis include medications like:

• Corticosteroids
• Immunosuppressants
• Intravenous immunoglobulin

Your provider or a physical therapist will give you stretches and exercises to keep your affected muscles flexible and strong. This can help reduce pain, stiffness and how much you’re affected by future episodes.

When should I see my healthcare provider?

Visit a healthcare provider right away if you experience new muscle weakness, pain or other symptoms — especially if they don’t get better in a few days. Talk to your provider if the symptoms get worse or spread to other parts of your body.

Go to the emergency room if you:

• Can’t move a part of your body you usually can
• Have trouble breathing
• Have trouble swallowing

What can I expect if I have idiopathic inflammatory myopathy?

In most cases, treatment can put myositis into remission. Most people with IIM have it for the rest of their lives.

Myositis can cause severe, potentially life-threatening complications. But this is rare. Your healthcare provider will tell you how often you’ll need checkups and tests. Monitoring your body for changes is the best way to prevent these issues. Talk to your provider right away if you notice any changes in the symptoms you have.