Polymyositis: The Daily PANCE Blueprint
A 45-year-old woman presents with progressive muscle weakness over the past three months. She reports difficulty climbing stairs and lifting objects. She has no skin rash. Her laboratory tests show elevated creatine kinase (CK) levels. Which of the following is the most appropriate next step in diagnosing her condition?
A. Skin biopsy
B. Electromyography (EMG)
C. Muscle biopsy
D. Antinuclear antibody (ANA) test
E. Magnetic resonance imaging (MRI) of muscles
Answer and topic summary
The answer is C. Muscle biopsy
In a patient presenting with symmetric proximal muscle weakness and elevated muscle enzymes without skin findings, a muscle biopsy is often necessary to confirm the diagnosis of polymyositis. The biopsy would demonstrate typical histopathologic findings such as endomysial infiltration by inflammatory cells, muscle fiber necrosis, and regeneration.
Incorrect Answers:
A. Skin biopsy – This is more relevant for diagnosing dermatomyositis, which presents with both skin and muscle involvement.
B. Electromyography (EMG) – While EMG can help differentiate myopathic from neuropathic causes of weakness, it is not definitive for polymyositis and is typically used to guide the location for muscle biopsy.
D. Antinuclear antibody (ANA) test – ANA testing can be positive in many autoimmune conditions but is not specific for polymyositis.
E. Magnetic resonance imaging (MRI) of muscles – MRI can show muscle inflammation and help in selecting a biopsy site, but it is not diagnostic of polymyositis on its own.
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Covered under ⇒ PANCE Blueprint Musculoskeletal (8%) ⇒ ⇒
