Polymyositis

Polymyositis is an autoimmune disease in which the immune system inflames skeletal muscles, causing weakness that develops over weeks to months. It mainly affects the muscles of the hips, thighs, shoulders and upper arms, making it hard to climb stairs, rise from a chair or lift the arms. Some people also have trouble swallowing or lung involvement. Many cases once called polymyositis are now classified as other forms of myositis, so specialist assessment matters.

Lab tests linked to polymyositis:

• Creatine kinase (CK): usually raised, reflecting muscle damage.
• Antinuclear antibody (ANA) by IFA and speckled pattern: often positive in myositis, but neither is specific.
• Doctors also order aldolase, a myositis antibody panel (such as anti-Jo-1), and lung tests. They may arrange an EMG, a muscle MRI and a muscle biopsy.

How results are read:

• A raised CK supports muscle inflammation, and it is also used to follow treatment response.
• A speckled ANA is common in many autoimmune conditions and in some healthy people.
• Myositis-specific antibodies help define the subtype. Anti-Jo-1, for example, is linked to lung disease.
• Diagnosis rests on the pattern of weakness, muscle imaging or biopsy, and antibodies, after other causes such as thyroid disease and medicines are ruled out.

When to see a doctor:

• See a doctor about weakness in the hips or shoulders that is getting worse over weeks.
• Get emergency care for difficulty breathing, rapidly worsening breathlessness, or choking when swallowing.

Clinical takeaway: polymyositis is suspected from proximal weakness with a raised CK, and myositis antibodies, imaging and biopsy help confirm it.