Myositis
What Is Myositis?
Myositis refers to the inflammation of muscle tissue, which can weaken muscles by disrupting their ability to contract properly. While muscle aches and tenderness can occur, muscle weakness is typically the most prominent symptom. Myositis can either be a short-term condition that resolves in a few days or weeks, or it can be part of a long-term chronic condition. In chronic cases, myositis can lead to muscle wasting and significant disability.
There are various types of myositis, including:
- Idiopathic inflammatory myopathies: This group includes conditions where the cause of muscle inflammation is unknown. The three primary types are dermatomyositis, polymyositis, and inclusion body myositis. These conditions are rare, affecting approximately 1 in 100,000 people in the U.S. Polymyositis and dermatomyositis are more common in women, while inclusion body myositis predominantly affects men. Polymyositis and dermatomyositis are believed to be autoimmune diseases, where the immune system attacks the body’s own muscle tissues.
- Infectious myositis: Muscle inflammation may also occur during a systemic infection, particularly viral infections like the flu. In some cases, parasitic infections, such as trichinosis, can cause myositis when undercooked meat is consumed. Pyomyositis, a bacterial infection that leads to pus-filled abscesses in the muscle, can occur, particularly in tropical climates or in individuals with HIV or those who inject drugs.
- Benign acute myositis: In young children, this form of myositis may occur after a viral illness, causing severe leg pain and difficulty walking. Symptoms usually resolve within a few days.
- Myositis ossificans: This condition occurs when bony deposits form within a muscle, usually after a deep bruise or injury.
- Drug-induced myositis: Certain medications, particularly statins (used to lower cholesterol) and drugs for HIV/AIDS, can cause muscle inflammation as a side effect.
Symptoms
The primary symptoms of myositis include:
- Muscle weakness, often accompanied by muscle pain or tenderness.
- In idiopathic inflammatory myopathies, muscle weakness typically develops gradually over weeks or months and often affects the muscles closest to the trunk (neck, shoulders, hips).
- Skin rashes, such as purple discoloration of the eyelids or red rashes on the face, knuckles, elbows, or knees, may accompany muscle weakness in dermatomyositis.
- In inclusion body myositis, muscle weakness often starts in the upper legs, wrists, and fingers and later affects the arms and lower legs. Muscle wasting may become prominent.
- In infectious myositis, symptoms may include fever, muscle aches, and additional signs depending on the specific infection (e.g., respiratory symptoms for flu-related myositis).
- Children with benign acute myositis typically experience sudden leg pain and difficulty walking, often following a respiratory infection.
- Myositis ossificans presents as a painful lump in a muscle following an injury.
- Drug-induced myositis usually involves muscle soreness, weakness, and pain after starting a new medication.
Diagnosis
To diagnose myositis, a doctor will review your symptoms, paying close attention to the location and duration of muscle weakness or pain. Common diagnostic tests include:
- Blood tests to detect muscle enzymes or antibodies that suggest inflammation or infection.
- Electromyography (EMG) to measure electrical activity in muscles.
- Imaging tests like MRI or CT scans to identify abnormal muscle tissue.
- A muscle biopsy, where a small tissue sample is examined under a microscope to confirm the diagnosis of myositis.
Duration
The duration of myositis depends on the type:
- Idiopathic inflammatory myopathies: These are typically chronic, with symptoms persisting for months or years. Treatment may lead to improvement, but some cases of inclusion body myositis do not respond to therapy.
- Infectious myositis: Flu-related myositis symptoms usually resolve in 3-7 days. Trichinosis can take several weeks to improve, and pyomyositis may require drainage and antibiotics, with recovery taking weeks to months.
- Benign acute myositis: Symptoms in children usually resolve within a few days.
- Myositis ossificans: Bony lumps may disappear on their own over months, though some cases may require surgical removal.
- Drug-induced myositis: Symptoms typically resolve once the medication is discontinued, but recovery may take several weeks or months.
Prevention
There are no specific preventive measures for most forms of myositis, as the causes are largely unknown. However, for infectious and drug-induced myositis, preventive steps include:
- Receiving a flu shot annually.
- Thoroughly cooking pork and other meats to prevent parasitic infections.
- Avoiding illegal drug use and ensuring clean injection sites for prescribed medications.
- Using the lowest effective dose of medications and monitoring for potential side effects.
Treatment
Treatment for myositis depends on the type:
- Idiopathic inflammatory myopathies: Treatment usually begins with corticosteroids such as prednisone. If corticosteroids are ineffective, other medications, including immunosuppressants like methotrexate, may be used. In some cases, intravenous immunoglobulin therapy can be effective.
- Infectious myositis: Treatment involves rest, fluids, and antiviral or antibiotic medications, depending on the infection. For bacterial infections like pyomyositis, drainage of abscesses and antibiotics are necessary.
- Benign acute myositis: Treatment typically involves pain relief, and symptoms usually resolve without further intervention.
- Myositis ossificans: If the bony lump does not disappear on its own, surgery may be necessary to remove it.
- Drug-induced myositis: Stopping the offending medication usually resolves symptoms, but corticosteroids may help speed up recovery.
Prognosis
The outlook for myositis varies:
- Idiopathic inflammatory myopathies: Many people respond well to treatment and regain muscle strength, though inclusion body myositis often does not improve significantly with treatment.
- Infectious myositis: Flu-related muscle symptoms usually resolve quickly. Recovery from trichinosis can be slow, but treatment is effective in most cases. For pyomyositis, early treatment is critical for a good prognosis.
- Benign acute myositis: Children typically recover fully within a few days.
- Myositis ossificans: The prognosis is good, especially if surgery is performed to remove persistent lumps.
- Drug-induced myositis: Symptoms usually subside once the drug is discontinued.
Further information
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.