BI32 Something fishy about that ulcer: a leg ulcer on an immunocompromised scuba diver

Abstract A 58-year-old man presented with an enlarging painful ulcer on his left medial knee. He had a history of psoriatic arthritis, on dual immunosuppression for the past 5 years with methotrexate and adalimumab. He had recently travelled to over 20 countries across five continents in 2 years, and his hobbies included scuba diving and seawater and freshwater swimming. One year prior to this presentation, he recalled freshwater swimming in a cave lake in the state of Bahia, Brazil without a wetsuit, where companions reported bites from tropical fish on the same day. From that time, he developed two small erythematous papules on each knee with rapid resolution on the right knee. His travel continued, with scuba dives in multiple countries in Central America, the Caribbean and Ireland in the months that followed. The left-knee lesion slowly enlarged, and he sought medical attention in Ireland 9 months later. He received penicillin antibiotics, topical steroids and mupirocin cream from his general practitioner. He was switched from adalimumab to infliximab for a presumed diagnosis of pyoderma gangrenosum by his treating rheumatology team. The lesion’s growth accelerated over the course of 8 weeks, ultimately leading to acute presentation to the emergency department with severe pain and limited mobility. On examination, he had a 20 × 10-cm eroded plaque on his left knee with an exudative base and a ragged erythematous and violaceous edge. He also had a 25 × 20-mm eroded lesion on his right flank, and a hyperpigmented patch on his right knee. He denied fevers or systemic symptoms. His blood serology was negative for hepatitis B, hepatitis C and HIV infection, and he was varicella immune. Interferon-γ release assay was positive, which had been negative in 2019 while on immunosuppression. A skin biopsy from the left-leg lesion demonstrated ulceration, mixed inflammation and underlying dermal necrosis, but no significant epidermal hyperplasia. Necrotizing granulomas were seen and Ziehl-Neelsen stain was positive for abundant acid-fast bacilli. Direct microscopy was positive for Mycobacterium. Subsequent biopsy from the right-flank lesion had similar findings. Chest X-ray showed no irregularities. A liver ultrasound was completed due to isolated raised alanine transferase, but showed no liver lesions. Full culture and sensitivity results are still pending, and an appropriate treatment regimen will be commenced following identification of the specific Mycobacterium. His immunosuppression is on hold, both ulcerated lesions continue to slowly enlarge and he remains under close review. This case demonstrates the importance of a full medical and social history, including hobbies and travel, in all patients on immunosuppressive therapy, as they are at risk of atypical infections and presentations.