SUN-404 Diabetes Insipidus and Hypopituitarism in a Patient with Transient Isolated Pituitary Stalk Enlargement

Background. The differential diagnosis of pituitary stalk lesions is broad and includes neoplastic, inflammatory, infectious, and congenital disorders. Lymphocytic infundibuloneurohypophysitis (LIN) has been identified as an etiology of transient pituitary stalk enlargement leading to permanent central diabetes insipidus (DI). We present a case of transient isolated pituitary stalk enlargement complicated by both central DI and hypopituitarism. Case. A 65-year-old male presented to hospital with polyuria, polydipsia, nausea and vomiting, and a 20 lb. unintentional weight loss over three weeks. Hypernatremia (149 mM, 133-142) and inappropriately dilute urine (180 mOsm/kg) were noted on admission. Treatment with desmopressin resulted in prompt resolution of polyuria and hypertonicity. MRI was notable for nodular thickening of the pituitary stalk and loss of the posterior pituitary bright spot on T-1 weighted images, and lumbar puncture yielded clear fluid with mild lymphocytic pleocytosis, no malignant cells, and unremarkable angiotensin converting enzyme level. Evaluation of anterior pituitary function revealed secondary adrenal insufficiency, secondary hypothyroidism, secondary hypogonadism, impaired somatotroph function, and mild hyperprolactinemia (16.2 ng/mL, 3.6-13.2). The patient recovered to baseline weight and well-being on treatment with hydrocortisone, thyroxine, and intramuscular testosterone. He declined biopsy in favor of serial imaging of the pituitary stalk. Over the course of 18 months, radiographic changes in the pituitary stalk resolved, though DI and anterior pituitary deficits persist. Conclusion. Radiographic lesions confined to the pituitary stalk present a significant diagnostic challenge because biopsies are difficult and potentially injurious to patients. Diagnosis is based mostly on clinical evaluation and imaging. Epidemiological data are sparse; out of 150,045 head MRI studies at Mayo Clinic from 1987-2006, 2,700 were reviewed due to mention of “pituitary stalk” or “infundibulum” and 152 were found to have a pituitary stalk abnormality. LIN has been demonstrated on biopsy in patients with central DI and reversible pituitary stalk enlargement. In a series of 17 adult patients with LIN, central DI was persistent despite improvement in pituitary stalk abnormalities, but anterior pituitary function was preserved. A more recent series of nine children with central DI and apparent LIN followed for a mean of five years found six patients with resolution of pituitary stalk abnormalities; central DI persisted in all patients, and only one experienced loss of anterior pituitary function. Though unusual, this case illustrates that LIN may be complicated by permanent hypopituitarism in addition to central DI, possibly by injury from undetectable extension of pituitary stalk inflammation to the pituitary gland or hypothalamus.