Endocrine Abstracts

Introduction: In addition to physiological causes, the hyperprolactinemia spectrum includes iatrogenesis, pituitary adenomas, various diseases and functional disorders. Hyperprolactinemia accurate etiological diagnosis is essential for appropriate treatment. Non-functioning pituitary incidentalomas occur in approximately 10% of the population and tiny microprolactinomas could be elusive to imaging by magnetic resonance (MRI). Therefore, the coincidence of hyperprolactinemia and a pituitary mass does not necessarily mean that the patient has a prolactinoma and vice-versa. Dynamic testing with dopamine antagonists to distinguish adenoma-related hyperprolactinaemia from other causes, such as metoclopramide test (MCPT), were described several decades ago. Although their use is not universal, they have been shown to be useful in the differential diagnosis of hyperprolactinemia. The MCPT protocol includes a fasting serum sample drawn to determine prolactin (PRL) and TSH at baseline (PRL0), taken 30' and 60' after 10 mg MCP IV injection. The relative PRL increase is calculated as (PRLmax-PRL0)/PRL0 expressed as percentage (%PRL). PRLmax is the highest PRL post-infusion. An absolute >2.1 mU/l increase in TSHmax over TSH0 indicates a high dopaminergic tone. Although there may be overlapping, generally a >100% increase in PRLmax over PRL0 is considered a normal response. Prolactinomas typically display a flat PRL response (usually <100% increase) with a >2.1 mU/l TSHmax increase.Material and MethodsWe selected 98 patients (80% female) with hyperprolactinemia who had undergone MCPT and pituitary MRI. Patients were divided into three groups according to PRLmax response: Group A (<100%) (N=35), Group B (≥100-300%) (n=16) and Group C (≥300%) (n=47).ResultsMean (range) PRL0, PRLmax (ng/dL) and%PRL increase were: GrA: 153 (41-1246), 171 (72-1214) and 45.5% (-7.1-97.8%); GrB: 123 (19-141), 281 (49-461) and 178.0% (106.9-272.8%); GrC: 31 (3-75), 257 (93-498) and 1470.8% (324.3-15224.0%). Mean (range) TSHmax (mU/mL) were: GrA: 2.4 (-2.2-11.2); GrB: 1.9 (-0.1-5.1); GrC: 0.5 (-1.9-3). A positive MRI pituitary image was found: GrA: 28/35 (80%); GrB: 9/16 (56%); GrC: 3/47 (6%). All 3 GrC microadenomas behaved like non-secreting incidentalomas.

ConclusionIn prolactinomas, the PRLmax after MCPT usually exhibits an increase <300%. Therefore, MCPT is superior to baseline PRL in accuracy regarding the origin of hyperprolactinaemia. MCPT results guide the therapeutic intervention and may reduce the need for a pituitary MRI.