AN AUDIT OF THE DIAGNOSTIC USEFULNESS OF PRL AND TSH RESPONSES TO DOMPERIDONE AND HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING OF THE PITUITARY IN THE EVALUATION OF HYPERPROLACTINEMIA

BACKGROUND AND OBJECTIVE The usefulness of dynamic tests of PRL releas e in determining underlying pathology in hyperprolactinaemic patients is not well recognized by endocrinologists, only 15% of whom routinely perform such tests. High resolution pituitary magnetic resonance imag ing (MRI) has become more widely available during the past 5 years and is now generally regarded as the pituitary imaging method of choice. Since few prolactinoma patients are now submitted to surgery, it is im portant to ascertain the usefulness of these techniques in suggesting a pathological diagnosis. DESIGN A 3 year retrospective audit of the i nformation derived from measurement of PRL and TSH responses to the do pamine antagonist domperidone and from high resolution pituitary MRI i n patients being investigated for hyperprolactinaemia in regional endo crine unit. PATIENTS Eighty-four patients (10 male, 74 female) whose i nvestigation of hyperprolactinaemia included a domperidone test and hi gh resolution pituitary MRI. Patients who had domperidone tests perfor med after pituitary surgery or who did not have pituitary MRI were exc luded from the analysis. MEASUREMENTS PRL and TSH were measured basall y and at 30 and 60 minutes following domperidone (10 mg i.v.) and gado linium-enhanced pituitary MRI was performed In all patients. RESULTS 2 0 patients had a normal PRL response to domperidone (defined as PRL30' /PRL0' > 3) and this group included five patients in whom hyperprolact inaemia was not sustained. Pituitary MRI showed evidence of a microade noma in only two patients, imaging being unequivocally normal in the m ajority. Sixty-four patients had an abnormal PRL response to domperido ne and 18 of these had a macrolesion (nine prolactinomas, nine other t umours). Pituitary MRI was performed in the remaining 46 patients with abnormal PRL response to domperidone and suggested microadenoma in 29 (63%), identified other structural abnormalities in six cases but was entirely normal in 11 cases. Neither the basal PRL level nor the TSH response could refine the diagnosis further because of overlap between the various subgroups. CONCLUSIONS The majority of patients with a no rmal dynamic response of PRL to domperidone had a normal or near norma l pituitary MRI scan. In the two cases where an abnormality was detect ed it could have been an incidental microadenoma or cyst, thus suggest ing that pituitary scanning could normally be omitted in patients whos e PRL response to domperidone is normal (24% of our total). The group of patients with an abnormal dynamic response of PRL to domperidone wa s not generally amenable to further diagnostic refinement by consideri ng the degree of hyperprolactinaemia or the TSH response to domperidon e because of overlap of these parameters between the diagnostic subgro ups. Therefore any degree of hyperprolactinaemia associated with a blu nted PRL response to domperidone warrants pituitary. imaging.