Summary

We present a rare case of a subscapularis pyomyositis in a 38-year-old woman and examine the diagnostic and surgical challenges posed. History and examination features were similar to that of septic shoulder arthritis without overlying features of warmth or erythema. Serological markers revealed a C-reactive protein of 221 mg/L and white cell count of 11.1×10⁹/L. A dry shoulder aspirate was obtained. Contrast-enhanced MRI demonstrated a peripheral rim-enhancing lesion within the subscapularis muscle belly with lack of central enhancement. These features are consistently seen with an infective aetiology. A deltopectoral approach to surgical drainage was utilised and subsequent fluid cultures grew Panton–Valentine Leukocidin positive Staphylococcus aureus species. This rare bacterium is associated with an increased risk of osteomyelitis and despite making a full recovery, the patient was advised to reattend if any future shoulder pain was encountered.