Two peas in a pod: A case of SIADH coexisting with pituitary macroadenoma.
P.C. Valsalakumari, A. Pokrajac
Dept. of Diabetes and Endocrinology, West Hertfordshire NHS Trust
SIADH is one of the most frequent causes of euvolemic hyponatraemia. There have been very few case reports in the literature describing a relationship between SIADH and pituitary tumors. We report a case of SIADH causing mild hyponatreamia in a patient with a nonfunctioning pituitary macroadenoma.
A 79 year old gentleman presented after a collapse episode on a background of severe nausea for the past 24 hours. Past medical history is significant for hypertension for which he is on Losartan. On examination he had bruising of his forehead and a significant postural drop in his blood pressure. Remaining system examination including neurological examination was unremarkable and he was clinically euvolemic.
Investigations and treatment:
Investigations showed hypotonic hyponatremia (serum sodium 126mmol/l, serum osmolarity 266mmol/kg) with urine osmolarity 519mmol/kg and urine sodium of 160mmol/l which confirmed a diagnosis of SIADH. A CT head showed swelling of the pituitary gland which was confirmed as a macroadenoma with supresellar extension without causing compression of the optic chiasm on subsequent MRI. Visual field assessment showed no field defect. CT whole body did not show any abnormality. His pituitary profile was within normal limits giving him a diagnosis of nonfunctioning pituitary adenoma. He was treated with fluid restriction which improved serum sodium gradually to 135mmol/l and he was referred to the neurosurgeons for further management of pituitary macroadenoma.
The underlying mechanism of increased arginine vasopressin secretion in pituitary masses is not clearly understood. One explanation is that a large pituitary mass may have provoked mechanical irritation of the AVP-producing cells in the supraoptic and paraventricular nuclei of the hypothalamus, a pathogenic mechanism that might have provoked SIADH in this patient. This case report indicates that SIADH may be more frequently associated with underlying pituitary masses than expected. This also proves it essential to monitor their progress after removal of the pituitary lesion in order to outline the possible underlying mechanism and to exclude other causes.