Inflammatory Myopathy

Overview

Inflammatory myopathy, also called myositis, is a group of disorders in which the body's immune system mistakenly attacks the muscles, causing inflammation. This inflammation damages muscle fibers and leads to muscle weakness, which is the hallmark of these conditions.

The group includes several distinct types, such as polymyositis, dermatomyositis (which also affects the skin), inclusion body myositis, and others. The weakness usually affects muscles closest to the center of the body, such as the hips, thighs, shoulders, and neck, making activities like climbing stairs, rising from a chair, or lifting the arms difficult. Inflammatory myopathies are uncommon and chronic, but with treatment that calms the immune system, many people can manage symptoms and maintain function.

Symptoms

Symptoms often develop gradually over weeks to months, though they can sometimes appear more quickly. Common features include:

• Muscle weakness, usually symmetric and affecting the hips, thighs, shoulders, upper arms, and neck.
• Difficulty with everyday tasks, such as climbing stairs, standing from a seated position, lifting objects, or raising the arms.
• Muscle fatigue and, in some people, muscle aches or tenderness.
• Difficulty swallowing if the throat muscles are affected.
• Skin changes in dermatomyositis, such as a rash on the eyelids, face, knuckles, or other areas.
• Tiredness and, in some types, shortness of breath if breathing muscles or the lungs are involved.

Inclusion body myositis tends to progress more slowly and may cause weakness in the hands and thighs, sometimes affecting one side more than the other.

Causes

The exact cause of inflammatory myopathy is not fully understood. These are largely autoimmune conditions, meaning the immune system attacks the body's own muscle tissue. Possible contributing factors include:

• Immune system dysfunction, which leads to inflammation of muscle fibers.
• Genetic susceptibility, which may make some people more prone to autoimmune disease.
• Environmental triggers, such as infections, in some cases, which may help set off the immune response.
• Associations with other autoimmune diseases and, in some adults with dermatomyositis, with cancer, which is why screening may be recommended.

Risk Factors

Factors that may increase the risk include:

• Sex, as some types are more common in women.
• Age, with certain types more likely in particular age groups; dermatomyositis can affect children and adults, while inclusion body myositis is more common in older adults.
• Having another autoimmune or connective tissue disease, such as lupus.
• A family history of autoimmune conditions.

Diagnosis

Diagnosing inflammatory myopathy involves combining the clinical picture with several tests, because the symptoms can resemble other muscle and nerve conditions. Evaluation may include:

• Medical history and examination, focusing on the pattern of weakness and any skin changes.
• Blood tests, including muscle enzymes such as creatine kinase, which are often elevated, and tests for specific autoantibodies.
• Electromyography (EMG), which records the electrical activity of muscles.
• MRI to identify inflamed muscles and guide further testing.
• Muscle biopsy, in which a small muscle sample is examined to confirm inflammation and identify the type.
• Additional tests to check for related conditions, lung involvement, and, when appropriate, cancer screening.

Treatment

Treatment aims to reduce inflammation, preserve and rebuild muscle strength, and manage complications. Because these are largely autoimmune conditions, treatment usually focuses on calming the immune system. Approaches include:

• Corticosteroids, often the first treatment to reduce inflammation, sometimes at higher doses initially and then tapered.
• Other immune-suppressing or immune-modulating medications, used to control the disease and reduce reliance on steroids.
• Physical and occupational therapy to maintain and improve strength, flexibility, and daily function.
• Speech and swallowing therapy if swallowing is affected.
• Treating skin involvement in dermatomyositis, including sun protection.
• Monitoring and managing complications, such as lung or heart involvement, and screening for associated conditions.

Inclusion body myositis tends to respond less well to immune treatments, so therapy and supportive care play a larger role. Care is often coordinated by a specialist such as a rheumatologist or neurologist.

Prevention

Inflammatory myopathy cannot be prevented because its exact cause is unknown and it is driven by the immune system. However, complications and flares can often be reduced by:

• Taking prescribed medications consistently and not stopping them suddenly.
• Staying active with guidance from a physical therapist to maintain strength.
• Attending regular follow-up appointments to monitor the disease and treatment.
• Protecting the skin from the sun in dermatomyositis.
• Reporting new symptoms, such as breathing or swallowing problems, promptly.

When to See a Doctor

See a healthcare provider if you have:

• Gradual, unexplained muscle weakness, especially in the hips, thighs, shoulders, or neck.
• Difficulty with tasks such as climbing stairs, standing up, or lifting your arms.
• A new rash along with muscle weakness.
• Difficulty swallowing.

Seek urgent or emergency care for severe difficulty swallowing, choking, or shortness of breath, as these can indicate involvement of the swallowing or breathing muscles or the lungs and need prompt attention. Early diagnosis and treatment can help protect muscle strength and prevent complications.

Related Topics

Frequently Asked Questions

References

1. National Institute of Neurological Disorders and Stroke (NINDS).
2. National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).
3. MedlinePlus, U.S. National Library of Medicine.
4. The Myositis Association.