Polymyositis

Diagnosis

Diagnosis of polymyositis typically involves a physical exam and an assessment of muscle strength. Several tests can help confirm the condition and rule out other causes of muscle weakness.

• Blood tests may show higher levels of muscle enzymes, which suggest muscle damage. They can also detect autoantibodies linked with specific symptoms of polymyositis.
• Electromyography involves placing a thin needle electrode into the muscle to measure electrical activity during muscle movement. Changes in electrical patterns can indicate muscle disease, and testing different muscles helps identify which ones are affected.
• MRI uses a magnetic field and radio waves to create detailed images of muscles. It can detect widespread inflammation and pinpoint areas of muscle involvement.
• Muscle biopsy may be needed for a definite diagnosis. A small sample of muscle tissue is removed and examined for signs of muscle damage and inflammation.
• Lung tests such as pulmonary function tests and a chest CT may be recommended, especially if certain autoantibodies are present that increase the risk of interstitial lung disease.

More information
CT scan
Electromyography
ENA test

Treatment

Although there is no cure for polymyositis, treatment can improve muscle strength and help muscles function better. Treatment decisions depend on symptoms and how well therapies manage those symptoms.

Medications
• Corticosteroids such as prednisone are commonly used and can control symptoms effectively. Because long-term use can cause serious side effects, the dosage is gradually lowered over time.
• Corticosteroid-sparing agents, including azathioprine and methotrexate, may reduce the need for high doses of corticosteroids and help prevent side effects.
• Medicines for more-serious illness, such as mycophenolate mofetil, cyclosporine, tacrolimus and rituximab, can reduce reliance on corticosteroids when symptoms are more severe or persistent.
• Intravenous immunoglobulin, or IVIg, contains healthy antibodies from donors that can block harmful antibodies attacking muscle tissue. It is given through a vein and may be used regularly or occasionally, especially for swallowing difficulties.

Therapy
Treatment plans may also include supportive therapies depending on the severity of symptoms:
• Physical therapy to improve muscle strength and guide safe activity levels
• Speech therapy if swallowing muscles are weakened
• Nutrition support with guidance from a registered dietitian to help maintain adequate nutrition when chewing or swallowing becomes difficult