A 67-year-old woman is referred to a neurologist complaining of difficulty getting out of her chair.
She is noted to have discrete erythematous papules over her metacarpophalangeal joints. Her creatine kinase (CK) is 4000.
What is your diagnosis?
Dermatomyositis
Myasthenia gravis
Myotonic dystrophy
Polymyositis
Polyneuropathy
Explanation:
Dermatomyositis is correct as the high CK, proximal muscle weakness and skin changes suggest dermatomyositis.
Dermatomyositis and polymyositis are related conditions that present with proximal muscle weakness. Dermatomyositis has cutaneous signs such as Gottron’s papules, discrete erythematous papules over metacarpophalangeal joints, and a heliotrope rash.
Myasthenia gravis and myotonic dystrophy are incorrect as they would not produce a pattern of either distal or proximal myopathy.
Polymyositis is incorrect as it is not associated with skin changes.
Polyneuropathy is incorrect as it produces a distal rather than proximal neuropathy.