Incidence and Clinical Significance of Elevated Macroprolactin Levels in Patients with Hyperprolactinemia

Abstract

To determine the prevalence and clinical characteristics of patients with macroprolactinemia in an endocrinology practice at a tertiary care military medical center in the United States. We reviewed the medical records of 40 patients who had been referred for evaluation of hyper-prolactinemia between June 2003 and August 2004 in whom macroprolactin had been measured. Of the 40 patients, 18 (9 men and 9 women) (45%) had an elevated macroprolactin level (mean, 75% of the total prolactin). The demographic characteristics of these patients were similar to those of patients with elevated monomeric prolactin. Most of the men with macro-prolactinemia (78%) had erectile dysfunction as the presenting complaint, whereas the most frequent symptom in women was menstrual irregularities (56%). Fifty percent of patients had no identifiable cause for their presenting complaint other than macroprolactinemia. Of the 18 patients with macroprolactinemia, 16 underwent magnetic resonance imaging (MRI) of the pituitary, of whom 56% had normal findings. Of the patients with abnormal MRI findings, 57% had a microadenoma, and 43% had either an atrophic anterior lobe or a prominent hypophysis. No significant relationship was detected between MRI findings or symptoms and the presence of elevated macroprolactin levels. Approximately 40% of patients in the macroprolactin group were treated with a dopamine agonist, 28% of whom had normalization of the total prolactin level. Although macroprolactin is commonly found in patients with hyperprolactinemia, neither symptoms nor MRI findings are useful in predicting its presence. Patients with macroprolactinemia often have symptoms similar to those in patients with elevation in monomeric prolactin. The clinical significance of macro-prolactinemia remains uncertain.