Adult onset multisystem Langerhans cell histiocytosis initially presenting with arginine vasopressin deficiency: a case report.

Background: Langerhans cell histiocytosis (LCH) is a rare hematopoietic disorder with diverse clinical presentations and sequential or concurrent multi-organ involvement. The adult onset is particularly uncommon and challenging to diagnose early. Case presentation: A 36-year-old female patient initially presented with polydipsia, polyuria, and dry mouth, gradually developing bone pain, facial erythema, and lymph node enlargement. Cranial MRI showed pituitary stalk thickening with the absence of a posterior pituitary signal. Iliac bone biopsy with immunohistochemistry demonstrated S-100(+), CD1a(+), and CD68(+) expression. After Systemic Chemotherapy and DDAVP administration, follow-up showed improvement of polyuria, polydipsia, and polyphagia, remission of osseous pain, regression of cutaneous manifestations, normalized pituitary stalk morphology, and reduced lesion metabolic activity. Conclusion: This report documents a complex and rare case to improve early diagnosis, reduce misdiagnosis, and prevent poor outcomes from delayed treatment.