Polymyositis Presenting as Rhabdomyolysis After the Initiation of Omeprazole

Rhabdomyolysis is a clinical syndrome with a wide range of presentations; it results in muscle necrosis and release of intracellular muscle contents into the circulation. Inflammatory myopathies are a rare cause of rhabdomyolysis. We present a case of a 46-year-old male with a two-week history of progressively worsening diffuse muscle pain after he had been prescribed omeprazole one month prior. A creatine phosphokinase (CPK) elevation was noted, which persisted despite treatment with IV fluids, sodium bicarbonate, and close correction of electrolytes. Further workup, including autoimmune and infectious etiologies, was notable for elevated antinuclear antibodies (ANA), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). Furthermore, a muscle biopsy showed evidence of endomysial inflammatory cells, consistent with a diagnosis of polymyositis. Steroids were initiated with significant improvement in symptoms and a decrease in CPK levels. The patient was discharged on a tapering dose of steroids and, on follow-up with the rheumatologist, transitioned to methotrexate with control of symptoms. In patients with rhabdomyolysis who do not respond to first-line therapy, obtaining a detailed medication history and screening with ANA and ESR are encouraged. Given the link between medication and autoimmune disease, clinicians should consider autoimmune myopathy in the differential for cases with persistently elevated creatine kinase. Prompt diagnosis with early initiation of immunosuppressive medication may improve outcomes and avoid complications associated with untreated rhabdomyolysis or polymyositis.