Intramuscular Aseptic Cyst Syndrome: A Case Report and a Review of the Literature.

Aseptic cyst syndrome (ACS) is a rare condition frequently associated with a systemic inflammatory response. The clinical presentation closely mimics an infection, making diagnosis and treatment challenging. The most common location of aseptic abscesses is intra-abdominal. Intramuscular involvement is highly uncommon, typically affecting muscles near the trunk. This report presents a case of a male patient who developed multiple aseptic abscesses in the hamstrings and proximal gastrocnemius (GM) muscles. The patient initially underwent surgical debridement and cyst resection, followed by intravenous antibiotic therapy. Although there was a brief period of improvement, a relapse occurred, marked by renewed pain, fever, elevated infection biomarkers, and knee joint effusion. The patient was ultimately treated with corticosteroids, followed by immunosuppressant therapy, resulting in rapid disease improvement. No recurrence was observed at the final follow-up, nine months after symptom onset. A narrative review of the literature on this topic is also included. This case underscores the importance of high clinical suspicion and a multidisciplinary approach in the diagnosis and management of ACS.