Elevated serum prolactin level in the Zollinger-Ellison syndrome.

To estimate the prevalence of prolactinoma in the Zollinger-Ellison syndrome (ZES), serum prolactin (PRL) levels were measured by radioimmunoassay in 36 patients with ZES. Eight patients had elevated PRL levels; however, in one patient the finding was attributed to primary hypothyroidism rather than a prolactinoma. The seven other patients were believed to have previously undiagnosed prolactinomas on the basis of elevated serum PRL levels; the presence of pituitary tumors were confirmed in four by demonstration of sella turcica erosions or enlargement. Serial determinations over three to six years showed a tendency for serum PRL levels to increase modestly in four of six patients. Thus far, two patients have undergone transsphenoidal tumor resections with good results. This study suggests that the prevalence of prolactinoma in patients with ZES is substantial (10% for those with isolated ZES and 54% for those with ZES with multiple endocrine neoplasia, type 1, syndrome), and that early diagnosis is possible with measurement of serum PRL levels. Since levels of PRL tend to increase and clinically significant pituitary tumors can develop, determinations of serial serum PRL levels are recommended for all patients with ZES.