Autoimmune Myositis Presenting With Fulminant Rhabdomyolysis and Dialysis-Dependent Acute Kidney Injury in the Context of Nitrofurantoin Exposure and Chronic Statin Use: A Case Report.

Autoimmune inflammatory myopathies (AIM) can present insidiously or abruptly and are often indistinguishable from drug-induced myopathy. Severe rhabdomyolysis with acute kidney injury (AKI) as a complication in an elderly patient is a high-stakes presentation. We present a case of a 77-year-old woman on long-standing atorvastatin therapy who presented with an acute onset of proximal lower-limb weakness, CK > 42,000 U/L, stage 3 AKI, and transaminitis a week after a short course of nitrofurantoin. Magnetic resonance imaging (MRI) and electromyography (EMG) confirmed inflammatory myopathy; serology was positive for Mi-2α and PL-7 antibodies but negative for 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase antibodies. Despite statin withdrawal and cessation of nitrofurantoin and vigorous fluid resuscitation, she needed hemodialysis. High-dose intravenous methylprednisolone therapy followed by oral prednisolone resulted in clinical recovery as well as resolution of biochemical abnormalities, with CK returning to normal at discharge (189 U/L). This case demonstrates the coexistence of drug-induced myopathy and double myositis antibody positivity (anti-Mi-2α and anti-PL-7) resulting in AKI requiring dialysis, and a favorable response to corticosteroid therapy without the need for IVIG. In older adults presenting with marked CK elevation and renal failure, AIM should be considered as one of the differential diagnoses, even in the context of concurrent statin exposure. Myositis-specific antibody pattern, including the uncommon double-positive combination, serves as an important guide for diagnosis and initial immunosuppression, while drug cessation alone may not achieve adequate disease control.