MON-138 Hypothalamic-PituitaryInfiltration by Langerhans CellHistiocytosis

Abstract Disclosure: Z. Flores-Guerrero: None. O.A. Velasco-Espinosa: None. F. Martinez-Sanchez: None. F.J. Gomez-Perez: None. D. Cuevas-Ramos: None. Langerhans cell histiocytosis (LCH) is a rare disease characterized by the proliferation of cells of the mononuclear phagocytic system. It is predominantly diagnosed in childhood (∼3 years), with 30% of cases occurring in adults. Its incidence in patients older than 15 years is 1-2 cases per million. Hypothalamic-pituitary region (HPR) infiltration occurs in 5-50% of cases, with arginine-vasopressin central deficiency (AVP-D) being the most common endocrine manifestation, reported in 15-50%.Here we present our case-series of patients with biopsy-confirmed LCH in any affected organ and clinical, biochemical, and/or radiological evidence of HPR infiltration. Demographic data, signs and symptoms, presentation, hormonal deficiencies, radiological findings, and treatments were analyzed. Continuous variables were described as medians with 25-75 percentiles, and categorical variables as frequencies.Nine patients (six men) were included, with a median follow-up of 2.4 years (1.5-5.7). Seven were diagnosed in childhood (2-5 years) and two in adulthood (27-30 years). The median age at diagnosis of HPR infiltration was 3 years (2-27). The most frequent symptoms were polydipsia-polyuria and skin lesions. All patients developed AVP-D; three had anterior pituitary deficiencies and one developed corticotropic insufficiency post-treatment. Skin (4/9) and bone (4/9) were the most affected organs. One patient had isolated pituitary involvement during recurrence. Five had pituitary involvement initially, none isolated. Although pituitary biopsies were not performed, HPR infiltration was confirmed by clinical, biochemical and therapeutic response criteria. One patient underwent a pituitary MRI, which showed hyperintensity and thickening of the infundibulum, hypothalamic involvement, and absence of the T1-sequence posterior lobe bright spot, typical findings of HPR infiltration. All patients received chemotherapy and hormonal replacement therapy (HRT); however, none recovered hormonal function. Follow-up MRIs in five cases showed resolution of the infiltration in four patients, with persistent but reduced involvement in one.HPR infiltration ​​secondary to LCH underlines the need to recognize this condition as a potential cause of pituitary dysfunction. It can occur at any stage of the disease, whether isolated or with multi-organ involvement. While AVP-D is the most frequent manifestation, present in all patients in this series, anterior pituitary deficiencies are also present in a significant number of cases (3/9), often overlooked due to lack of intentional investigation, particularly in adults. Despite the lack of hormonal recovery, it is crucial to assess all hormonal axes at diagnosis and follow-up, offering appropriate HRT in a timely manner. Although biopsy is the gold standard, diagnosis can be based on clinical, biochemical and radiological criteria. Presentation: Monday, July 14, 2025