Extensive vulvar and perianal langerhans cell histiocytosis with clinical improvement during low-dose thalidomide and topical therapy: a case report.

Langerhans cell histiocytosis (LCH) involving the female genital region is uncommon and can closely resemble chronic inflammatory, infectious, or neoplastic vulvar diseases. We report a case of a 35-year-old woman with a 6-month history of recurrent painful brownish-red plaques, nodules, erosions, and ulcerations that began in the perianal region and subsequently extended to the vulva. Topical fusidic acid only provided temporary symptomatic relief. Histopathological examination revealed epidermal erosion and crusting, acanthosis, elongated rete ridges, and a dense dermal and subcutaneous infiltrate containing numerous large histiocytes with pale eosinophilic cytoplasm and focal nuclear grooves. Immunohistochemical analysis revealed that the lesional cells exhibited positivity for S100, CD1a, and langerin and negative for HMB45, SOX10, ALK-1A4, and BRAF V600E. Broader molecular testing for MAPK-pathway alterations was not performed, and the lesion was therefore described as BRAF V600E-immunonegative rather than genetically BRAF/MAPK wild type. The pathological diagnosis was vulvar LCH, with clinically suspected involvement of the perianal region. Positron emission tomography/computed tomography (PET/CT) revealed an enlarged cervical lymph node, with no other abnormalities documented; its relationship to LCH could not be determined. Oral thalidomide (50 mg nightly) was subsequently administered while topical Pevisone was continued. Symptomatic improvement, particularly pain relief, was observed after 1 week, and further clinical improvement of the anogenital lesions was documented at 3 months. Because both therapies were used concomitantly, the independent contribution of thalidomide could not be determined. This case underscores the diagnostic challenges associated with anogenital LCH and documents short-term clinical improvement during a low-dose thalidomide-containing regimen without establishing thalidomide monotherapy efficacy. It also highlights the necessity for biopsy, comprehensive systemic evaluation, and ongoing follow-up.