Diagnosis of Lymphocytic Infundibuloneurohypophysitis After Positive Anti-rabphilin-3A Antibody Test in an 8-year-old Boy with Early-onset Central Diabetes Insipidus

Childhood-onset lymphocytic infundibuloneurohypophysitis (LINH) has rarely been reported. Pathological evaluation via pituitary biopsy is necessary for a definitive diagnosis of LINH. However, pituitary biopsy is a highly invasive procedure. Recently, anti-rabphilin-3A antibody (RPH3A-Ab) has been reported as a promising diagnostic marker for LINH in adults but.there are few reports of this association in the pediatric population. We report the case of an 8-year-old boy with central diabetes insipidus (CDI) who was diagnosed clinically with LINH, based on RPH3A-Ab positivity. He was initially diagnosed with CDI using a water deprivation test combined with desmopressin administration. Serum and cerebrospinal fluid tumor markers were negative, and T1-weighted magnetic resonance imaging (MRI) revealed the absence of high signal intensity in the posterior pituitary gland and an enlarged pituitary stalk. Anterior pituitary function tests revealed no abnormalities. No pituitary biopsy was performed because of its invasive nature, and desmopressin treatment was initiated. Three months after the diagnosis of CDI, the patient tested positive for RPH3A-Ab. MRI performed nine months after CDI diagnosis revealed amelioration of the pituitary stalk enlargement, and this clinical course corroborated our diagnosis of LINH. RPH3AAb may be useful as an early diagnostic tool for LINH in the pediatric population.