Brief Overview: Polymyositis is a rare idiopathic inflammatory myopathy that causes muscle weakness and inflammation. This can cause difficulty with things like walking up and down stairs, lifting things, reaching overhead, and getting up from sitting. Of note, the term polymyositis is being used less and less as many cases can now be better classified/diagnosed otherwise.
Prevalence: Polymyositis is uncommon. The annual incidence of PM has been reported to be 0.41 to 0.75 per 100,000 persons, according to UpToDate.
Etiology: Polymyositis is idiopathic (the cause is unknown).
Risk Factors:
- Female
- Age (children are rarely affected)
- Autoimmune diagnosis present
Commonly Associated Conditions:
- Interstitial Lung Disease (ILD)
- Cardiac involvement – conduction abnormalities and arrhythmias found on ECG
- Inflammatory arthritis
- Raynaud’s phenomenon
- Lupus
- Systemic sclerosis
Common Medications:
- Systemic glucocorticoids
- csDMARD – ex: methotrexate, azathioprine, mycophenolate
- IVIG – for patients with severe disease
Common Labs, Imaging, and Tests:
- Muscle biopsy – to rule out other diagnoses
- Muscle enzymes: Creatine Kinase (CK), lactate dehydrogenase (LDH), aldolase, AST, ALT
- ANA
- ESR, CRP
- TSH
- Myositis-specific autoantibody panel, anti-NT5C1a antibodies, anti-HMGCR antibodies, myositis-associated autoantibodies
- CBC with differential
- CMP
- Chest X-ray
- Pulmonary function test (PFT)
- MRI
- EMG
Common Symptoms:
- Skeletal muscle weakness, especially symmetric proximal muscle (muscles closest to the body – muscles in the neck, shoulders, hips, thighs) weakness
- Myalgia
- Muscle tenderness
- Joint pain and swelling
- Dysphagia (difficulty swallowing)
- Shortness of breath
- Fatigue
Common Treatments:
- Medication (see above)
- Physical therapy
- Exercise (discuss exercise recommendations with your healthcare provider)
- Speech therapy (if dysphagia is present)
- Treatment of any associated conditions
Physical Findings:
- Symmetric proximal muscle weakness
- Muscle tenderness
- Weight loss may be present
- ECG changes/abnormalities may be present
- Low grade fever may be present
- Gait abnormalities/changes
Potential Complications and Contraindications:
- Progression/worsening of symptoms
- Increased risk for heart attack
- Increased rate of cancer
- Osteoporosis
- Increased risk for infections
- Aspiration risk if dysphagia is present
- Increased fall risk
- Medication side effects
- If on immunosuppressants, increased infection risk
General Health and Lifestyle Guidance:
- Fall risk prevention
- Balanced diet
- Rest as needed
- Alert your healthcare provider to any new or worsening symptoms
- Discuss any age-appropriate vaccines with your healthcare provider, especially if on immunosuppressants (like pneumonia vaccine, flu shot, shingles shot, etc.)
Suggested Questions to Ask Patients:
- Have you had increasing difficulty with tasks like climbing stairs or lifting objects?
- Do you experience muscle pain or unusual fatigue after minimal activity?
- Have you noticed trouble swallowing or changes in your voice?
- Are you currently taking corticosteroids or immunosuppressants?
- Do you have a history of lung or autoimmune conditions?
Suggested Talking Points:
- This condition may be managed by multiple specialists
- Elevate head of bed if dysphagia is present
- Discuss any specific dietary recommendations with your healthcare provider
- Staying active, as tolerated, can be helpful
Sources:
- UpToDate
- Cleveland Clinic
- Johns Hopkins Medicine
- org