Inflammatory Myopathies

Inflammatory myopathies are muscle diseases caused by inflammation. They are autoimmune diseases where the body’s immune system attacks its own muscles by mistake. The most common inflammatory myopathies are dermatomyositis and polymyositis; however, this is a rapidly evolving field and new inflammatory myopathies are being described. Inflammatory myopathies cause muscle weakness, usually in the neck, shoulders, and hips. Dermatomyositis causes skin rashes also. Muscle weakness is a common symptom. Some people can have breathing problems. People of all ages and races may get inflammatory myopathies, but they’re rare. Children usually get them between ages 5 and 10. Adults usually get these diseases between 40 and 50. Women get inflammatory myopathies twice as often as men.

What Are the Signs/Symptoms?

The most common sign of inflammatory myopathies is weakness in the large muscles of the shoulders, neck, or hips. Inflammation damages tissue so you lose strength in these muscles. Inflammatory myopathies may cause problems like these:

• Trouble climbing stairs, lifting obects over your head, or getting out of a seat
• Choking while eating or intake of food into the lungs
• Shortness of breath and cough
• Dermatomyositis causes skin rashes that look like red or purple spots on the eyelids, or scaly, red bumps on the elbows, knuckles, or knees
• Children may also develop calcinosis, white spots on their skin from calcium deposits, or vasculitis, a blood vessels inflammation that leads to skin lesion.

What Are Common Treatments?

Diagnosing inflammatory myopathies starts with a muscle strength exam. A rheumatologist may also do blood tests to measure muscle enzymes and myositis-specific antibodies, electromyogram (EMG) to measure electrical activity in the muscles, or magnetic resonance imaging (MRI) to look for muscle damage. You may need a muscle biopsy. These diseases may be linked to cancer, so tests to rule out cancer may be needed. The first treatment for inflammatory myopathies is an oral corticosteroid, such as prednisone, at high dose. Muscle enzymes usually return to normal at 4 to 6 weeks, and strength returns in 2 to 3 months. Your doctor may add other drugs to your treatment plan, like methotrexate or azathioprine, for long-term disease control and to avoid long-term side effect of corticosteroid. Some patients with severe disease may need intravenous immunoglobulin (IVIG), cyclosporine (Neoral, Sandimmune), tacrolimus (Prograf), mycophenolate mofetil (CellCept), or rituximab (Rituxan).

Living with Inflammatory Myopathies

Good health habits are important for long-term management of inflammatory myopathies. Eat a healthy, well-balanced diet, get regular exercise, and stay at a healthy weight. People with dermatomyositis should use sun protection so rashes don’t worsen. Limit your time outdoors and use sunscreen when you go outside. If you have trouble swallowing, eat soft foods or puree solid foods in a blender. To prevent choking if you are bedbound, sit up in bed to eat. People with myopathy may look healthy and normal. It is important for employers, teachers, and family members to understand the limits that muscle weakness causes in people with myopathy.

Updated February 2023 by Howard Yang MD, and reviewed by the American College of Rheumatology Committee on Communications and Marketing.

This information is provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.