Increased body weight associated with prolactin secreting pituitary adenomas: weight loss with normalization of prolactin levels

OBJECTIVE Hyperprolactinaemia in humans may be associated with a high prevalence of obesity but the nature of this link is poorly defined. The aim of this study was to establish the relationship between hyperprolactinaemia and body weight in patients with prolactin-secreting pituitary tumours. DESIGN We conducted a retrospective study of prolactinoma patients treated at the Endocrine Institute of the Tel Aviv Medical Center, Israel, during the period 1989-1996, Patients with clinically nonfunctioning pituitary macroadenomas (NFA) served as the control group. Data on demographic parameters, body weight before and during treatment, clinical presentation including history of weight fluctuations, tumour size as measured by computed tomography or magnetic resonance imaging, modalities and response to treatment, and pituitary function before and during treatment were recorded from medical files. PATIENTS Forty-two patients with prolactinomas (PR) and 36 patients with clinically non-functioning macroadenomas (NFA) comprised the study population. RESULTS Mean weight was 93 +/- 3.4 kg and 78 +/- 2.7 kg in male patients with PR and NFA respectively (P=0.0007). Recent weight gain (8 to 22 kg) was a presenting symptom in 13 PR patients, whereas only one NFA patient had this clinical presentation (P=0.001). Seventeen PR patients lost weight(mean change -8.3 +/- 1.5 kg, range -2-28 kg), during prolactin lowering therapy, 11 of whom had entirely normalized prolactin levels, Fourteen of the 18 patients who did not lose weight still had elevated prolactin levels (P=0.01). Weight loss in patients with PR could not be attributed to altered pituitary function nor to compression of the third ventricle, In contrast to PR, no significant weight loss was observed in NFA patients. CONCLUSION Weight gain and elevated body weight are frequently associated with prolactinomas regardless of a mass effect on the hypothalamus or pituitary function. In this series, weight loss was recorded in 70% of prolactinomas patients and in 90% of male patients who normalized their prolactin levels. We propose the inclusion of hyperprolactinaemia in the differential diagnosis of endocrine obesity and weight gain.