Polymyositis: Causes, Symptoms and Treatment
Polymyositis is a rare inflammatory muscle disease in which the immune system attacks the body's own muscle tissue, causing progressive muscle weakness and requiring medical treatment.
Things worth knowing about "Polymyositis"
Polymyositis is a rare inflammatory muscle disease in which the immune system attacks the body's own muscle tissue, causing progressive muscle weakness and requiring medical treatment.
What is Polymyositis?
Polymyositis is a chronic inflammatory disease of the skeletal muscles and belongs to the group of idiopathic inflammatory myopathies (IIM). In this condition, the body's immune system mistakenly attacks muscle cells, leading to inflammation and progressive muscle weakness. The disease primarily affects the proximal muscles, meaning the muscles closest to the trunk, such as those in the shoulders, upper arms, hips, and thighs. Women are more commonly affected than men, and the disease most often develops between the ages of 40 and 60.
Causes
The exact cause of polymyositis has not yet been fully understood. It is classified as an autoimmune disease, in which T-lymphocytes (a type of white blood cell) invade muscle tissue and cause damage. Possible contributing factors include:
- Genetic predisposition (certain HLA gene variants)
- Viral infections (e.g., Coxsackievirus or HIV)
- Certain medications as rare triggers
- Co-existing autoimmune conditions
In some cases, polymyositis occurs alongside other connective tissue diseases such as lupus erythematosus or systemic sclerosis.
Symptoms
The hallmark symptom of polymyositis is a symmetrical, proximal muscle weakness that develops gradually. Common complaints include:
- Difficulty rising from a seated position or climbing stairs
- Weakness when lifting the arms above the head
- Difficulty swallowing (dysphagia) when throat muscles are involved
- Muscle pain and tenderness
- General fatigue and exhaustion
- In severe cases: breathing difficulties if the respiratory muscles are affected
Unlike dermatomyositis, polymyositis typically does not present with characteristic skin changes.
Diagnosis
Diagnosing polymyositis requires a combination of several investigations:
- Blood tests: Elevated muscle enzymes such as creatine kinase (CK), lactate dehydrogenase (LDH), and aldolase indicate muscle damage. Specific autoantibodies (e.g., anti-Jo-1) may also be detected.
- Electromyography (EMG): This test measures electrical activity in muscles and can reveal typical patterns of inflammatory myopathy.
- MRI of the muscles: Imaging to identify areas of inflammation within muscle tissue.
- Muscle biopsy: The removal and microscopic examination of a small sample of muscle tissue is the most important diagnostic step and confirms the diagnosis.
Treatment
The goals of treatment are to suppress inflammation, preserve muscle function, and prevent complications. Treatment options include:
Medication-Based Therapy
- Corticosteroids (e.g., prednisone): Considered the first-line treatment. They are started at high doses and gradually tapered.
- Immunosuppressants: If corticosteroids are not sufficiently effective or to reduce the steroid dose, medications such as azathioprine, methotrexate, or mycophenolate mofetil may be used.
- Intravenous immunoglobulins (IVIG): May be administered in severe cases or when other treatments have not been effective.
- Biologics: In certain cases, newer agents such as rituximab may be considered.
Non-Medication Therapy
- Physical therapy: Targeted muscle exercises to maintain and improve muscle strength.
- Occupational therapy: Support for managing daily activities.
- Speech therapy: For patients with swallowing difficulties to address affected muscles.
Prognosis and Disease Course
The course of polymyositis varies from person to person. Many patients respond well to immunosuppressive therapy and experience significant improvement in muscle function. However, some individuals follow a chronic course with flares and remissions. Long-term complications can include lung involvement (interstitial lung disease), cardiac involvement, or an elevated cancer risk, which is why regular medical follow-up is essential.
References
- Dalakas MC. Inflammatory muscle diseases. New England Journal of Medicine. 2015;372(18):1734-1747.
- Lundberg IE, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies. Annals of the Rheumatic Diseases. 2017;76(12):1955-1964.
- Mammen AL. Autoimmune muscle disease. Continuum: Lifelong Learning in Neurology. 2020;26(6):1596-1615.
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