SUN-017 LYMPHOCYTIC INFUNDIBULO NEUROHYPOPHYSITIS IN A MAN

Abstract Disclosure: D.R. Ávila Salcedo: None. J.A. Ayala San Pedro: None. L.M. Martínez Borja: None. P.A. Montes Hernández: None. R.S. Sánchez García: None. Lymphocytic infundibuloneurohypophysitis (NIHL) is a rare condition that affects the adenohypophysis in 65% of cases (almost exclusively in women), the neurohypophysis in 10% (equal in both sexes) and a combination of the two in 25% (predominantly in women). Clinical case: 24-year-old man. Presented with polyuria, polydipsia, nocturia associated with hypernatremia 157 mmol/L, urinary osmolality 128 mOsm/L and post-desmopressin 20 µg of 377 mOsm/L. Cortisol 12.6 µg/dL (synacthen test), TSH 1.18 µIU/mL, T4f 1.19 ng/dL, testosterone 280 µg/dL, LH 3 µIU/mL. MRI with hyperintensity of the infundibulum, with contrast enhancement. Figure 1a. Other studies: ANA 1:180, ANCA 1:160, AMA centrosome 1:160, Quantiferon-TB negative, and IgG4 negative. Diagnosed with central diabetes insipidus, secondary adrenal insufficiency and hypogonadotropic hypogonadism due to NIHL, without meeting SLE criteria, ANCA vasculitis despite positive antibodies. Treatment with nasal desmopressin 10 µg bid, achieving remission of polyuria by the third day. In addition to prednisone 40 mg QD, with resolution of the infundibular lesion (figure 1b) and recovery of the hypothalamic-pituitary axis, after 45 days.The diagnosis consists of three pillars: 1) biochemical evaluation, 2) imaging evaluation, and 3) evaluation of secondary causes such as inflammatory, infectious or neoplastic processes. Although biopsy is the gold standard for the diagnosis of INHL, it is contraindicated in patients without evidence of mass effect, due to the risk of adverse events. The characteristics that support the diagnosis are: a thickening of >4 mm of the pituitary stalk plus the absence of hyperintensity of the neurohypophysis is highly suggestive of INHL; on the other hand, lesions of neoplastic origin are usually associated with a greater thickening of the pituitary stalk, being male and young. Anti-rabfilina-3A antibodies have a specificity of 96.2% and a sensitivity of 100% for the diagnosis of INHL. Treatment with glucocorticoids is associated with a recovery of anterior pituitary function (OR 3.41; CI, 1.68-6.94) and a regression of lesions on imaging (OR 3.13; CI, 1.54-6.36) compared to observation. In the case presented, diagnosis was possible thanks to the combination of the most common clinical presentation, such as CID, neuroimaging findings, evidence of autoimmunity (we do not have anti-rabfilina-3A), absence of infections and an adequate therapeutic response. It is important to recognize that this pathology can represent the initial manifestation of an underlying systemic disease, which underlines the need for a comprehensive diagnostic approach and follow-up to identify possible comorbidities. Presentation: Sunday, July 13, 2025