Prolactinoma and systemic lupus erythematosus: do serum prolactin levels matter?

The lactogenic hormone prolactin is produced in part by cells of the immune system and serves as an upregulator of immune function. Hyperprolactinemia is common in patients with systemic lupus erythematosus (SLE), raising the possibility that the hormone contributes to the excessive immune response in the disease. The highest levels of circulating prolactin occur in association with prolactin-secreting tumors, but prolactinomas have only rarely been encountered in patients with SLE. We present here three patients with SLE and prolactinomas. As with the previously reported six patients, there was no consistency in the presence of findings related to prolactin excess or in the coincidence of hyperprolactinemia with flares of SLE disease activity. We speculate that this may be due to genetic differences in the response to prolactin and/or to the presence of variant prolactin isoforms detected in the clinical immunoassay that have reduced or absent biologic activity.