Pituitary tumors in MEN1: do not be misled by borderline elevated prolactin levels.

PURPOSE

The objective of this case report is to demonstrate that the simple expedient of measuring periodic prolactin levels in patients with MEN1 who have modest hyperprolactinemia and normal pituitary MRI scans is insufficient to monitor for the development of pituitary adenomas.

METHODS

Review of relevant literature and chart review.

RESULTS

A 25 year old man with known MEN1 manifested by hyperparathyroidism and a gastrin-producing neuroendocrine tumor was found to have a prolactin [PRL] level of 20.0 ng/mL [1.6-16 ng/mL] but a normal pituitary MRI scan. The impression then was that he had prolactinoma too small to be visualized on the MRI. Over the next 3.5 years his PRL levels remained in this mildly elevated range but he then presented with severe headaches and visual field defects. An MRI showed a 3.1 × 1.7 × 1.9 cm pituitary adenoma with compression of the optic chiasm and invasion of the left cavernous sinus. Surgery revealed a gonadotroph adenoma and he subsequently required gamma knife radiotherapy for residual tumor. Postoperative PRL levels were normal.

CONCLUSIONS

Small, intrasellar microadenomas may be associated with elevated PRL levels due to possible direct hormone production [prolactinoma] or possibly to interference with portal vessel blood flow. In monitoring hyperprolactinemic MEN1 patients for the development of pituitary adenomas, measurement of PRL levels is insufficient and periodic MRI scans are necessary at a more frequent interval than every 3-5 years. This may also pertain to patients with "idiopathic" hyperprolactinemia.