Post-Streptococcal Myositis: Etiology of Myalgia and Severe Inflammation in a Child

Streptococcus pyogenes (GAS) is responsible for many pediatric infections. Although outcomes are generally favorable with prompt diagnosis and treatment, it is necessary for pediatricians to remain vigilant for complications. We discuss a rare GAS complication: post-streptococcal myositis. An 8-year-old female patient recently hospitalized for cervical lymphadenitis presented with extremity pain and difficulty walking. Initial work-up revealed marked nonspecific inflammation, normal creatine kinase (CK), and superficial thrombophlebitis. Her symptoms progressed rapidly to high fevers, erythematous nodules, severe pain and edema, and superficial thrombophlebitis extension despite antibiotics and nonsteroidal anti-inflammatory pharmacotherapy. This was associated with rising inflammatory markers, extensive myositis of the extremities and mild fasciitis of the calves on imaging, and a muscle biopsy with normal architecture and no evidence of vasculitis or necrosis. A markedly elevated anti-streptolysin O (ASO) and anti-DNase B led to the diagnosis of post-streptococcal myositis. Symptoms responded rapidly to systemic steroids, with complete recovery within 5 months. Limited case reports of post-streptococcal myositis exist, which similarly describe severe myalgia and fevers, inflammation, elevated ASO, and typically normal CK. Most describe a self-limited disease course. This case describes a unique manifestation and sequelae of streptococcal infection in a child with an impressive degree of systemic inflammation and thrombotic complications. This report also describes pediatric muscle biopsy results in association with this diagnosis. Post-streptococcal myositis should be considered for patients with severe unexplained inflammation and myalgia.