Abstract
A macro pituitary tumour or giant pituitary tumour is regarded as a rare causal factor in syndrome of inappropriate antidiuretic hormone (SIADH) cases. Previous reports have presented findings showing that blood flow insufficiency related to stress caused by an obstructive mass may lead to inappropriate secretion of arginine vasopressin. On the other hand, prolactin is known to influence water metabolism, and several cases of a macroprolactinoma or giant prolactinoma (PRLoma) in patients with SIADH have been reported. Nevertheless, few studies have examined such a relationship with SIADH and discussion of pathophysiological factors has been limited. The present report provides details of an elderly patient with SIADH in a chronic giant PRLoma. Of note, exacerbation of prolactin level accompanied the occurrence of SIADH. Findings obtained in this case suggest the possibility of development of SIADH in PRLoma cases due to more than only the effect of the mass.