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A 57-year-old woman, previously well and taking no medications, gave a 2 - week history of progressive swallowing difficulty, nasal speech, nasal food regurgitation and mild limb girdle weakness . Two months before, she had developed a rash on her neck and behind her ears; by the time of presentation, this had spread to her face, scalp, elbows, knees and hands. She had no myalgia, arthralgia, fever or Raynaud’s phenomenon. Examination showed a skin rash (figure 1), weak palatal movements, absent gag reflex and mild hip flexion and shoulder abduction weakness. She required nasogastric tube feeding due to severe dysphagia.
What is the differential diagnosis?
Subacute onset of bulbar palsy raises a limited number of diagnostic possibilities. Intrinsic lower brainstem lesions, motor neuron disease, Guillain-Barré syndrome, myasthenia gravis and multiple lower cranial nerve palsies should be considered, although none of these would explain the rash. Inflammatory myopathies such as inclusion body myositis and dermatomyositis can present in this fashion. In this case, skin rash might suggest dermatomyositis.
Blood testing identified a serum creatine kinase concentration of 433 U/L (normal 30–180). Blood testing for vasculitis, systemic connective tissue diseases, myasthenia gravis and Lambert-Eaton myasthenic syndrome were negative or normal. Central nervous system imaging was unremarkable. Nerve conduction studies found no evidence of neuropathy and no decrement on repetitive nerve stimulation. Electromyography demonstrated low-amplitude, short-duration potentials.
What is the likely diagnosis and what tests would you perform?
Low-amplitude, short-duration muscle action potentials on electromyography suggest a myopathy. This finding, combined with dysphagia and skin rash, suggests a diagnosis of dermatomyositis. Historically, this diagnosis relied on clinical, biochemical (raised serum creatine kinase) and electromyography findings, combined with muscle histology showing perivascular endomysial inflammation and perifascicular atrophy.1 Nowadays, however, …
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