(760) Unmasking a Rare Infectious Complication of Th2 Pathway Inhibition: A Case of Iliopsoas Abscess Post-Dupilumab.

Introduction/Rationale: Dupilumab, a non-immunosuppressive monoclonal antibody that reduces IL-4 and IL-13 signaling, has shown a favorable infection profile in clinical trials.

Methods: A 30-year-old male with a history of asthma and atopic eczema was transferred from an outside hospital. He initially presented with two weeks history of severe back pain radiating to the right hip and thigh. He had received two doses of dupilumab three weeks before this presentation. CT scan of the pelvis revealed right sacroiliac joint septic arthritis with a 3.2 x 1.9 cm collection between the right gluteus area and the right iliopsoas abscess. He was treated with intravenous (IV) vancomycin and ampicillin-sulbactam for 10 days. Repeat CT scan showed no significant improvement; he was transferred to our institution for interventional radiology-guided drainage of the abscess. He underwent the drainage, which yielded purulent fluid. IV vancomycin, cefepime, and metronidazole were initiated. The fluid for bacterial, acid-fast and fungal cultures was negative. Blood cultures showed no growth. Laboratory studies showed elevated inflammatory markers and a negative autoimmune workup. Due to persistent fevers, antibiotics were changed to IV daptomycin, cefepime, and metronidazole.MRI of the right thigh on day 8 revealed a large multiloculated gluteal abscess (9 x 2.5 x 2.5 cm) and minimal iliopsoas involvement.
Due to the deep location and loculated lesion, the drainage was not feasible, and he was treated with 10 weeks of IV antibiotics. Repeat MRI showed complete resolution of abscesses and normalization of inflammatory markers, and the patient improved clinically.

Results: Dupilumab has non-immunosuppressive effects in trials; however, its inhibition of IL-4 and IL-13 may gradually modify host responses to bacterial infections by affecting Th2/Th1 balance, macrophage activation, or skin and mucosal barrier function.

Conclusion: As dupilumab's use expands, clinicians should remain vigilant for its rare but serious infectious complications.