© Under License of Creative Commons Attribution 3.0 License Title: Streptococcal Myositis or Septic Arthritis in A Young Child: A Diagnostic Challenge

Background: Septic arthritis is an orthopaedic emergency that can lead to significant morbidity and mortality if treatment is delayed. Myositis can present in a similar way to septic arthritis, particularly in a young child, but is treated differently. Clinicians must take both into account when assessing patients. Case Description: A five-year-old girl presented with a swollen, sore knee on a background of minor trauma. Examination findings revealed severe sepsis, tonsillitis and a florid rash suspicious of scarlet fever. An orthopaedic opinion was requested for the possibility of septic arthritis of the knee. Due to swelling of the thigh, a provisional diagnosis of myositis secondary to Group A Streptococcal throat infection was made and confirmed by MRI scan of the lower leg. The patient was transferred to an intensive care unit for monitoring and antibiotic therapy. Literature Review: There are reports of myositis being mistakenly diagnosed as septic arthritis of the knee leading to iatrogenic septic arthritis as a result of needle aspiration. Clinical Relevance: This highlights the diagnostic challenge posed in the case of a young, septic child who presens with a swollen, painful limb. Repeated clinical examination and the judicious use of magnetic resonance scanning assists in this situation