Abstract
The patient was a 33-year-old woman who was admitted for detailed examination due to symptoms of thirst, polydipsia, and polyuria that had developed seven months earlier. Polyuria (5,000-8,000 mL/day) and hyposthenuria (osmolality, 113 mOsm/L) were observed, and plasma osmolality was slightly elevated at 296 mOsm/L. Urinary osmolality did not increase on the water deprivation test, but increased following administration of pitressin. Plasma vasopressin was not elevated on the 5% hypertonic saline loading test. In addition, anterior pituitary function was normal. Brain MRI showed a marked enlargement of the pituitary stalk that was homogeneously enhanced, in addition to loss of high signal intensity in the posterior pituitary gland on T1-weighted imaging. Based on these findings, the patient was diagnosed with central diabetes insipidus resulting from lymphocytic infundibuloneurohypophysitis (LIN), and was given 10 μg/day desmopressin (DDAVP) nasal spray. Urine volume decreased to 1,500-2,000 mL/day, and subjective symptoms also disappeared. Administration of 20 mg/day prednisolone was subsequently initiated to suppress pituitary stalk inflammation, and MRI images taken approximately one month later showed marked improvement in pituitary stalk enlargement. However, as no clinical improvements in diabetes insipidus were observed, the patient is currently still receiving DDAVP, although six years have been already passed following the disease onset. Investigation of case reports of LIN treated using steroids revealed that while cases of remission and improvement of diabetes insipidus were observed when steroid therapy was initiated within one to five months of the onset of symptoms, no cases of improvement were observed when steroid therapy was initiated later than five months after their onset. These data suggest that steroid therapy for LIN must be started as early as possible in order to clinically improve diabetes insipidus.
