A Case of COVID-19-Triggered Polymyositis Leading to Rhabdomyolysis

SARS-COVID-19 is known to manifest with a wide variety of symptoms, most of which are respiratory. Myalgias are a common symptom of COVID-19, but cases of severe virus-induced inflammatory muscle injury leading to rhabdomyolysis and polymyositis have also been reported. Here, we present and discuss a case of a 56-year-old woman who presented with an initial presentation of COVID-19 infection with inflammatory polymyositis leading to rhabdomyolysis. The patient was first treated for rhabdomyolysis with aggressive fluid resuscitation with intravenous normal saline without improvement in symptoms. She was then started on high-dose intravenous methylprednisolone for presumed immune-mediated polymyositis. An MRI of the bilateral lower extremities and a biopsy of the left thigh confirmed inflammatory myositis. After the initiation of steroids, liver function tests and creatinine kinase levels trended down, and symptoms improved. The patient was discharged with a prednisone taper and completely recovered at a follow-up six months later. Post-COVID severe musculoskeletal involvement, including polymyositis or rhabdomyolysis, is rare, with only a few other cases published so far. Viral myositis, supported by myopathological evidence, should be considered carefully in patients with a recent COVID-19 infection after ruling out more common causes of myositis. Some proposed mechanisms include direct infection of the muscle or an environmental event triggering autoimmunity. Treatment generally involves corticosteroids that are gradually tapered.