What is Polymyositis?
Polymyositis is autoimmune inflammation of the muscles without the rash seen in dermatomyositis. It causes symmetrical weakness of the shoulders and hips developing over weeks to months, making stairs, standing from a chair and overhead reaching progressively harder. It is diagnosed by excluding the many conditions that mimic it.
Also called: PM
Who gets Polymyositis?
Usually adults over 20, more often women. It is a diagnosis made with care, because several conditions produce similar weakness and enzyme elevation: statin-associated and other drug-induced myopathies, inclusion body myositis, muscular dystrophies presenting in adulthood, thyroid disease, and metabolic myopathies. Genuine polymyositis is less common than the label suggests, and a confident diagnosis changes treatment substantially.
What are the symptoms of Polymyositis?
Not everyone has every symptom below, and having one does not confirm the diagnosis. These are the features that most often lead to assessment:
- Progressive difficulty with stairs, standing from sitting, or rising from the floor
- Difficulty lifting the arms to comb hair or reach a shelf
- Symmetrical weakness affecting shoulders and hips more than hands and feet
- Muscle aching and tenderness, though weakness dominates
- Difficulty swallowing or a change in voice
- Breathlessness or dry cough where lungs are involved
- Joint pain, Raynaud's phenomenon and cracked skin on the fingers, in antisynthetase syndrome
- Fatigue, low-grade fever and weight loss
How is Polymyositis diagnosed?
Muscle enzymes, particularly CK, are usually substantially raised. Thyroid function, vitamin D and a medication review — statins in particular — come first, since these explain a proportion of cases.
EMG distinguishes muscle disease from nerve disease. MRI of the thighs identifies inflamed muscle and the best biopsy site.
Muscle biopsy is important here, both to confirm inflammation and to exclude inclusion body myositis, which looks similar clinically but does not respond to immunosuppression — treating it as polymyositis exposes patients to years of unnecessary immunosuppression.
Myositis antibodies, chest CT and lung function tests complete the assessment.
How is Polymyositis treated?
Corticosteroids at high dose initially, with a steroid-sparing agent — methotrexate or azathioprine — introduced early so that steroids can be tapered.
Resistant disease is treated with intravenous immunoglobulin, mycophenolate, rituximab or tacrolimus.
Structured physiotherapy is essential and begins as soon as the acute inflammation is controlled. Exercise was once discouraged in myositis; the evidence now clearly supports supervised progressive exercise as part of treatment.
Swallowing and respiratory function are monitored, and lung involvement is treated in its own right.
Living with Polymyositis
Strength returns over months rather than weeks, and physiotherapy through that period determines much of the outcome. Long-term steroid effects are anticipated with bone protection and glucose monitoring. If weakness does not respond as expected, the diagnosis is revisited — inclusion body myositis is the commonest alternative and needs a different approach.
When should you see a rheumatologist?
Progressive symmetrical weakness of the shoulders and hips over weeks to months, especially with a raised CK, should be assessed promptly. Swallowing difficulty or breathlessness makes it urgent.
Common questions about Polymyositis
Could my statin be causing this?
It is one of the first things checked. Statins can cause muscle aching, enzyme elevation, and — less often — an immune-mediated necrotizing myopathy that continues after the drug is stopped and needs immunosuppression. Distinguishing these matters.
Should I exercise or rest?
Exercise, under guidance. Supervised progressive exercise is now an established part of treatment. Prolonged rest causes muscle loss on top of the disease, and that loss then has to be regained separately.
Why is a muscle biopsy necessary?
Chiefly to exclude inclusion body myositis, which looks similar but does not respond to immunosuppression. Treating it as polymyositis means years of unnecessary medication without benefit.
This page is general information to support a consultation. It is not a diagnosis, and it does not replace an assessment by a doctor who has examined you.