Background: Hypophysitis involving only the stalk and posterior pituitary, called Infundibulo Neurohypophysitis (INH), is a rare condition. Posterior pituitary involvement manifesting as central DI is the most common feature. Anterior pituitary involvement in the setting of hypophysitis usually affects corticotrophs, thyrotrophs and gonadotrophs in order of decreasing frequency¹. We report a case of INH causing gonadotropin deficiency at presentation.
Clinical Case: A 36 years old refugee from Afghanistan presented with 4 months history of polyuria (urine output 11 liters/day), polydipsia and decreased libido. Initial tests confirmed DI (serum osmolality 304 mOsm/kg, paired urine osmolality 64 mOsm/kg). He was euglycaemic (fasting Blood glucose level 5.4 mmol/l, HbA1c 5.5 %) with normal electrolytes. (C.Ca 2.23 mmol/L (2.20-2.60), K 3.87 mmol/L (3.50-5.0).
Anterior pituitary hormone functions showed hypogonadotrophic hypogonadism (LH 0.4 IU/L (1-9), FSH 0.9 IU/L (1-12), Testosterone 1.1 nmol/L (9-35), with normal IGF-1 14 nmol/L (10-40), Prolactin 228 mIU/L (60-400), FT4 13.9 pmol/L (9-19) and TSH 1.72 mu/L (0.4-3.50). He had preserved adreno-cortical axis with peak cortisol following 250mcg synacthen being 733 mmol/l. MRI revealed absence of posterior pituitary bright spot along with a 6X6X6mm nodule in the stalk which was isointense to pituitary on T1 and T2 weighted images with uniform enhancement post contrast. CT scan of chest, abdomen and pelvis showed no evidence of malignancy or granulomatous disease. Bone scan did not show any lesions consistent with metastatic disease or Langerhans cell histiocytosis. CSF exam revealed undetectable b-HCG (<1 IU/L). CSF cytology was negative and AFB culture showed no growth. ANCA, ANA and alpha feto-protein were negative.
He was treated with desmopressin nasal spray with marked clinical improvement. After discussion with the neurosurgeons, biopsy was not done. Repeat MRI and pituitary function tests after 03 months were unchanged. Options for testosterone replacement were discussed. He is on 3 monthly follow up indefinitely.
Discussion: Hypogonadotropic hypogonadism as the only anterior pituitary hormone deficiency in infundibulo-neurohypophysitis is rare². In the absence of tissue diagnosis by biopsy, careful exclusion of all other causes of stalk involvement, serial pituitary function tests and imaging is needed to ascertain evolving hormone deficiencies.