Abstract
Polymyositis is a rare disease with incidence rates at about 1 per 100,000 people annually. In this case report we will review a case of proximal muscle weakness with an elevated creatine phosphokinase that was initially misdiagnosed twice as rhabdomyolysis. Therefore, emphasizing that idiopathic inflammatory myopathy is a potential cause of myasthenia that must be considered in the differential. The case will also describe the current treatment and treatment response in polymyositis.
Highlights
When a clinician is confronted with a case of muscle weakness in the setting of a severely elevated creatine phosphokinase by probability alone, the most likely culprit is rhabdomyolysis
In the setting of an elevated CPK the differential diagnosis for myasthenia is narrowed to rhabdomyolysis or a myopathy
While acute exertional rhabdomyolysis can be diagnosed by history, the syndrome of idiopathic inflammatory myopathies must be differentiated from myopathies caused by infections, toxins, paraneoplastic syndrome, and endocrinopathies
Summary
When a clinician is confronted with a case of muscle weakness in the setting of a severely elevated creatine phosphokinase by probability alone, the most likely culprit is rhabdomyolysis. This is reflected in the abundance of medical literature citing cases of rhabdomyolysis This case report highlights a patient who presented with symptoms of an elevated creatine kinase and myasthenia, but was eventually diagnosed with an idiopathic inflammatory myopathy. Our case reviews why the presence of proximal muscle weakness, an elevated creatinine phosphokinase, and systemic clues should raise the clinician’s suspicion for these poorly understand idiopathic inflammatory myopathies. Case A 64-year-old man presented with two weeks of progressive proximal muscle weakness causing him difficulty ambulating, combing his hair, and raising himself from a seated position He reported dysphagia to solids over the past week. A muscle biopsy of the right deltoid was negative for inflammation but presumed to not be representative He was started on oral Prednisone 60mg daily with resolution of symptoms including weakness and pain and normalization of creatine kinase within one month of starting therapy
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