Isolated Perianal Langerhans Cell Histiocytosis in a Human Immunodeficiency Virus-Positive Adult: A Rare Incidental finding

Abstract Introduction/Objective Langerhans cell histiocytosis (LCH) is a rare disorder characterized by abnormal proliferation of antigen-presenting cells, primarily Langerhans cells. Although it commonly affects bones, skin, and lungs, involvement of the gastrointestinal tract is rare. Specifically, isolated perianal LCH is exceptionally uncommon, with only a few documented cases reported in the literature. Here, we report a case of incidental perianal LCH in an adult HIV patient, highlighting the exceptional rarity and clinical importance of this occurrence. Methods/Case Report A 56-year-old Caucasian male with HIV underwent surgical resection of a 0.5 x 0.4 x 0.3 cm verrucous lesion on the posterior anal margin. His past medical history included granulomatous lymphadenitis, penile warts, and anal dysplasia. Microscopic examination of the excised tissue revealed Langerhans cells with characteristic features, including abundant eosinophilic cytoplasm and irregular nuclear membranes (resembling “coffee-bean” or “folded paper” appearance). Immunohistochemical analysis confirmed the diagnosis by demonstrating positivity for CD1a, S100, and CD68. The BRAF mutation was evaluated on the same paraffin-embedded block, which revealed the lack of the mutant BRAF V600E. PET-CT imaging showed no evidence of metastatic disease, emphasizing the isolated nature of the perianal LCH in this patient. Results (if a Case Study enter NA) NA Conclusion This case highlights the significance of recognizing and thoroughly evaluating rare and incidental conditions such as LCH in HIV patients. Our findings emphasize the importance of maintaining a high index of suspicion for LCH among healthcare providers and ensuring proper follow-up to rule out systemic involvement. Furthermore, there is a need for future studies to investigate the correlation between LCH and HIV. Given its rarity and diverse clinical presentation in immunocompromised individuals, a multidisciplinary approach, tailored treatment plans, and long-term surveillance with imaging modalities like PET/CT are essential for effectively managing adult-onset isolated LCH.