Neuroinfundibulitis: Pituitary Stalk Thickening Presenting as Diabetes Insipidus

Background: Isolated pituitary stalk thickening (PST) from neuroinfundibulitis is a rare entity that requires thorough evaluation of secondary causes and understanding of treatment options. Clinical Case: A 55-year-old male presented with progressive polyuria and polydipsia over several months. He had no significant head injuries, headache, weight loss, fatigue or inability to exercise. His serum sodium level was 148 (135 - 145 mmol/L) with a serum osmolality 310 (275-305 mOsm/kg), and urine osmolality was 246 (40-1200 mOsm/kg) suggestive of partial diabetes insipidus (DI). A 24-hour urine collection had a volume of 9.2 liters. He had a normal hemoglobin A1c. Hormonal work-up was unremarkable with normal range his prolactin, IGF-1, and a.m. cortisol (19 mcg/dl). He was already on levothyroxine with normal thyroid function tests and negative thyroid antibodies. Water deprivation testing confirmed a diagnosis of central DI and he was started on desmopressin. Magnetic resonance imaging (MRI) of the pituitary demonstrated diffuse PST with T2 hyperintensity and loss of normal T1 hyperintensity (“bright spot”) of the posterior pituitary. Repeat imaging 3 months later showed progressive thickening. He underwent full body positron emission tomography-computerized tomography (PET-CT) which demonstrated increased metabolism of the pituitary stalk, but no other suspicious uptake in other areas. Chest X-ray, tuberculin screen, angiotensin converting enzyme, and calcium were all normal. Patient underwent transsphenoidal stalk biopsy. Pathology demonstrated fibrosis and chronic inflammation without malignancy but otherwise was nondiagnostic. Based on these findings, he was presumed to have neuroinfundibulitis and is being actively followed with MRIs and labs. Conclusion: Isolated PST is exceedingly rare, especially in adults. The differential diagnosis includes neoplastic (germinomas, lymphoma, metastatic disease), autoimmune, and infiltrative disease (sarcoidosis, histiocytosis). One review of 38 adult patients with central DI and PST showed that almost half had neuroinfundibulitis. Of those, 4 were treated with corticosteroids and 7 were not. All patients showed reduction or resolution of PST on subsequent MRIs indicating that resolution of thickening can be spontaneous without steroid use, and can be followed by MRI and with hormone replacement for deficiencies (1). Because of the rarity of isolated neuroinfundibulitis, it is important that neoplastic and systemic diseases be ruled out in all patients with PST, as in the case of our patient. 1.Devuyst F, Kazakou P, Baleriaux D, Alexopoulou O, Burniat A, Salenave S, et al. Central diabetes insipidus and pituitary stalk thickening in adults: distinction of neoplastic from non-neoplastic lesions. European Journal of Endocrinology. 2020;183(1):95-105.