Case Presentation: A 32-year-old woman with a history of hypertension presented with diffuse myalgias, generalized weakness, and mild nausea after attending an exercise class. She denied fever, abdominal pain, chest pain, or dyspnea. Initial laboratory evaluation showed a creatine kinase (CK) level >22,000 U/L, while her complete blood count and comprehensive metabolic panel were within normal limits. She was admitted for management of rhabdomyolysis and received aggressive intravenous fluid resuscitation. Despite three days of continuous hydration, her CK levels remained persistently above 22,000 U/L and her symptoms did not improve. On hospital day three, intravenous corticosteroids were initiated due to concern for an inflammatory myopathy. Within 24 hours, her CK decreased to 15,000 U/L and further declined to 8,000 U/L the following day, accompanied by marked clinical improvement. Autoimmune testing including ANA, anti–Jo-1, and other myositis-specific antibodies were sent to evaluate for autoimmune myositis.
Discussion: Rhabdomyolysis is most often caused by trauma, toxins, or exertion, but persistent CK elevation despite adequate hydration should raise suspicion for autoimmune myopathy. Polymyositis and other inflammatory myositides can initially manifest after minor exertion, leading to misdiagnosis as exercise-induced rhabdomyolysis. This patient’s refractory CK levels and rapid improvement after steroid initiation supported an underlying inflammatory process.Failure to consider autoimmune etiologies may delay appropriate therapy and prolong morbidity. Early recognition and initiation of immunosuppressive treatment can prevent chronic muscle injury and disability. Clinicians should use CK trajectory, symptom persistence, and treatment response to guide further evaluation beyond common causes of rhabdomyolysis.
Conclusions: Not all rhabdomyolysis is benign or exertional. Persistent CK elevation despite hydration should prompt an autoimmune workup. Early identification of inflammatory myositis and timely corticosteroid therapy can result in rapid biochemical and symptomatic recovery. Maintaining a broad differential helps prevent diagnostic anchoring and ensures appropriate management of complex muscle disorders.