S3706 Perianal Langerhans Cell Histiocytosis: Report and Diagnosis of Rare Cause of Severe Anal Pain

Introduction: Langerhans cell histiocytosis (LCH) is a rare disorder that can manifest as a focal or multisystem disease characterized by clonal proliferation of myeloid precursors that differentiate into Langerhans cells, accumulate in tissue, and potentially cause organ dysfunction due to the inflammatory response. Limited pediatric cases of focal perianal LCH lesions are reported in literature, and such cases are exceedingly rare in adults. Perianal lesions mimicking condyloma accuminata or condyloma lata in appearance encompass a broad differential including lymphoma, melanoma, signet ring carcinoma, and LCH and require immunohistochemistry for accurate diagnosis. Case Description/Methods: A 37-year-old man without significant medical history presented to primary care for severe anal pain of 2 months duration exacerbated by bowel movements. Exam under anesthesia revealed a posterior midline anal fissure with an adjacent skin tag excised by electrocautery. Histopathology noted diffuse nodular interstitial cellular infiltrate composed of large atypical pleomorphic cells with irregular infolded nuclei accompanied by prominent eosinophils. Immunohistochemical staining was strongly positive for CD1a, S100, and CD163 markers, supporting a diagnosis of LCH. Whole body positron emission tomography imaging did not show evidence of systemic disease. With adequate excision and healing of the perianal lesion, the patient’s symptoms resolved without recurrence after 10 months of close follow up. Surveillance imaging and further treatment was recommended in case of recurrent symptoms. Discussion: LCH can manifest as a unifocal or multifocal and single or multisystem disease and requires a thorough workup to initiate appropriate treatment and long-term management. Although rare, focal lesions of LCH can involve the GI tract including the perianal region. Histopathologic examination findings that support the diagnosis of LCH include lesional histiocytes with elongated, grooved, or folded nuclei with an eosinophilic infiltrate. Given the broad differential diagnoses of perianal lesions, immunohistochemistry is necessary for accurate diagnosis and management. LCH lesions are positive for CD1a, S100, and CD207. Positive CD163 staining occurs in only 5-10% of LCH cases. Alternative to the systemic treatment recommended for multifocal multisystem disease, unifocal LCH in adults can be adequately treated with intralesional steroids, radiation, or surgical resection.