An Unusual Case of Giant Polymicrobial Shoulder Abscess Developing Two Decades After an Insect Bite: The Role of Chronic Intermittent Swelling as a Predisposing Factor

Shoulder abscesses, commonly resulting from bacterial infections, can occasionally present with atypical etiologies and delayed onset. We report a rare case of a massive polymicrobial shoulder abscess developing two decades after an insect bite, emphasizing its clinical presentation, diagnostic approach, and surgical management. A 65-year-old female presented with severe, progressively worsening right shoulder pain, a 20 cm swelling, and purulent discharge persisting for 15 days. Her medical history revealed hypertension, diabetes, and intermittent swelling in the insect-bitten region over the years, which likely predisposed the area to recurrent infections. No evidence of autoimmune disorders, corticosteroid use, or dental abscess was identified. Clinical examination revealed a purulent yellow discharge from the superolateral region of the right shoulder. Ultrasonography and contrast-enhanced MRI confirmed a localized subcutaneous abscess without muscle invasion. The surgical intervention included open irrigation and debridement, revealing dense, purulent, caseous, malodorous material with necrotic debris. Microbiological analysis identified anaerobic streptococci, anaerobic gram-negative bacilli, anaerobic non-spore-forming gram-positive rods, <i>Corynebacterium</i> species, and methicillin-sensitive <i>Staphylococcus aureus</i> (MSSA), with no evidence of <i>Mycobacterium tuberculosis</i>. The pathogens were sensitive to ampicillin-sulbactam. The patient underwent a 10-day intravenous ampicillin-sulbactam regimen, followed by a one-month course of oral amoxicillin-clavulanic acid. The deep wound cavity was managed with vacuum-assisted closure (VAC) therapy for ten sessions, significantly aiding recovery. Complete healing with restored shoulder mobility was achieved. This case highlights the importance of considering unusual etiologies, such as delayed complications from insect bites, in shoulder abscesses. The patient's history of intermittent swelling in the affected area likely predisposed it to infection. Prompt surgical intervention, appropriate antibiotic therapy, and advanced wound care techniques, including VAC therapy, were pivotal in achieving successful outcomes. Immediate initiation of targeted antibiotics post-sampling effectively managed this polymicrobial infection with a simplified antibiotic regimen.