Marginally elevated prolactin levels require magnetic resonance imaging and evaluation for acromegaly.

Marginal elevations in serum PRL concentration represent a particularly difficult diagnostic dilemma. In most cases, mild hyperprolactinemia is not associated with organic disease. Patients with menstrual disturbances, galactorrhea, and confirmed elevations in serum PRL should have a screening TSH to rule out primary hypothyroidism (5). In cases where there is no clear etiology of hyperprolactinemia, an MRI should be performed. Magnetic resonance imaging with gadolinium is more sensitive and specific than CT scanning in detecting all types of pituitary tumors and is the study of choice (4). Further, a serum IGF-1 level (or OGTT) should be obtained when clinical symptoms and/or a pituitary mass suggest the possibility of acromegaly. An individual with abnormal GH screening tests but an unremarkable MRI would be subjected to an especially careful follow-up, including IGF-1 and PRL levels every 6 to 12 months. In this way, early tumor growth may be detected making a surgical cure more likely (Fig. 1). Although we have stressed the importance of GH-producing tumors as a cause of hyperprolactinemia, other tumor types of the pituitary may do so as well. Most of these will be detected by MRI.