Macroprolactinaemia associated with prolactin adenoma.

Abstract

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. 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. 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. Our results suggest that PRL adenoma may be associated with macroprolactinaemia.