Macroprolactinaemia associated with prolactin adenoma

Abstract

Background: Macroprolactinaemia, defined as hyperprolactinaemia with a predominance of, or only, the big big prolactin (bbPRL) isoform, is considered idiopathic and poorly symptomatic. Since its association with a PRL adenoma is poorly documented, we examined a series of 13 patients with tumoral hyperprolactinaemia for the presence of macroprolactinaemia. Methods: From a series of 36 patients with hyperprolactinaemia studied for PRL isoforms, we selected 13 with hyperprolactinaemia and a prolactinoma, and divided them into two groups on the basis of the predominant PRL isoform, the large PRL group (five patients), with a predominance of the big big PRL isoform, and the monomeric PRL (mPRL) group (eight patients), with a predominance of the mPRL isoform. Plasma PRL concentrations were measured by radioimmunoassay, while plasma PRL heterogeneity was studied by gel filtration chromatography. The plasma autoantibody-bound PRL and the histology of the tumours were also studied. Results: Macroprolactinaemia was seen in five out of the 13 patients with a PRL adenoma. The clinical and biological characteristics of the groups with and without macroprolactinaemia were similar. In the large PRL group, no evidence for anti-PRL autoantibodies was found and the prolactinomas were either typical or exhibited unusual aggregates of immunoreactive PRL deposits, the latter suggesting the tumoral origin of these large forms. Conclusion: Our results suggest that PRL adenoma may be associated with macroprolactinaemia.