P3D329: Severe COVID Myositis in a Healthy Adolescent

Introduction: Acute benign childhood myositis is a well-documented condition hypothesized to be caused by direct viral invasion of the muscle. While classically associated with influenza type B, it has also been associated with HIV, HSV, EBV, VZV, and most recently SARS-CoV-2. The progression from COVID myalgias to rhabdomyolysis is a rare complication and most often seen in pediatric patients with Multisystem Inflammatory Syndrome in Children (MIS-C). We report a case of severe viral myositis associated with severe myalgias and contractures with drastically elevated creatine kinase levels developed during an active SARS-CoV-2 infection in a previously healthy adolescent.

Case Description: 12-year-old female with no past medical history presented to the Emergency Department for dark urine after testing positive with an at-home COVID test 3 days prior. Her initial COVID symptoms included a mild cough and myalgias; the cough had resolved with improving myalgias until day 3 of illness when the patient noticed dark brown urine and worsening myalgias in the proximal muscle groups of the upper and lower extremities as well as her trunk. There were no reports of oliguria or anuria. Her exam was notable for normal blood pressure, significant tenderness to palpation in the proximal thighs, arms, and trunk associated with 3/5 strength and normal neurologic exam. Labs were significant for CK 875,760 (units), urinalysis positive for blood and protein, normal potassium, CRP, and serum Cr at 0.50. She was admitted under the presumed diagnosis of viral myositis. Throughout her hospital course she received aggressive hydration and never developed AKI. Pediatric rheumatology was consulted and high dose steroids and anakinra (IL-1 receptor antagonist) were started to inhibit suspected immune-mediated myositis. She was discharged on hospital day 8 with a down-trending CK and no AKI but severe muscle contractures and weakness. After outpatient wean of medications, she returned to full strength, range of motion, and activity level by 3 months from illness onset.

Discussion: This is a unique presentation of COVID-myositis/rhabdomyolysis considering the severity of CK elevation and weakness in an adolescent patient without significant medical history and without concern for MIS-C. COVID-related mortality is exceedingly low in pediatric and young adult populations without predisposing conditions. Although this case showed complete resolution of symptoms and lab abnormalities, it highlights a significant COVID-related morbidity. Considering the high viral load associated with this case as well as proposed mechanism of viral induced myositis, anakinra played a significant role as a safe steroid sparing agent.

Conclusion: Most documented cases of COVID myositis were found in adolescents but it has significant potential for short and long-term limitations on motor and strength development depending on age. Further research is necessary to identify the population at highest risk for COVID myositis and optimal management of this debilitating condition.