Cranial diabetes insipidus and possible prolactinoma-an interesting case
S Razvi & AJ McCulloch
Cranial diabetes mellitus is not usually associated with microprolactinomas. We report a 29 year old lady who presented 8 months after the birth of her only child with a 4 month history of polyurea and polydipsia. She had also noticed galactorrhoea and decreased libido although she had never breastfed the child and had not resumed normal menstrual function. The birth of her child was normal and uncomplicated although she admitted to being stressed recently since the baby was hospitalised with haemolytic uraemic syndrome.
Preliminary tests including calcium, thyroid, glucose and random cortisol were normal but a prolactin level was high at 1703 mu/l and serum sodium at upper limit of normal at 144mmol/l.
Cannulated prolactin levels were 1460 and 1560 mu/l, short synacthen test was normal and stimulation tests for anterior pituitary function were normal. Water deprivation showed some concentration of serum osmolality without an increase in urine osmolality. Desmopressin reversed this with urine osmolality doubling and urine volume shrinking . Visual fields were normal and an MRI of the pituitary showed a 1cm anterior mass, likely adenoma with loss of bright signal in the posterior pituitary consistent with cranial diabetes insipidus.
She was started on bromocriptine and DDAVP and her symptoms dramatically improved with undisturbed night`s sleep and no galactorrhoea. She declined the offer of pituitary surgery as a diagnostic and therapeutic option.
The lady is now well and repeat MRI scanning has shown that the mass has completely disappeared with an empty sella but normal function. She continues on the DDAVP and her symptoms of polyuria and polydipsia return on missing her dose
The absence of histology is unfortunate but the possibility remains that this could have been a prolactin producing adenoma with coexistent cranial diabetes insipidus . The other possibilities are lymphocytic hypophysitis or Sheehan`s syndrome as well as granulomatous diseases although the latter is less likely.