Endocrine Abstracts

Macroprolactin (MPL) is a complex of prolactin (PRL) and IgG. It is considered to have little bioactivity and may account for a significant proportion of patients with 'idiopathic hyperprolactinaemia'. We determined the prevalence of macroprolactinaemia in patients with hyperprolactinaemia and examined the clinical features. An Immuno-1 system with PEG precipitation was used to identify MPL, with a recovery of <50% taken as indicating significant macroprolactinaemia.
In Lothian Region over a 20 month period, 273 patients had total PRL >700 mU/L. MPL was found in 57 (21%) patients and the clinical records of 51 (44 female) were available for retrospective review.
The (mean plus/minus SD) age of patients was 41 plus/minus 13y. The median (range) concentrations for the various forms of prolactin were:- total PRL 1130 mU/L (728-5118), monomeric PRL 240 mU/L (<50-656) and MPL 895 mU/L (381-4854). Classical symptoms of hyperprolactinaemia was present in 51% of patients, including galactorrhoea (12%), menstrual disturbance (23% of women), infertility (11% of women) and decreased libido/erectile dysfunction (71% of men). Imaging was performed on 36 patients. Five had evidence of a microadenoma, one a pineal cyst and one a 10 mm macroadenoma (in this patient MPL was identified after the discovery of the tumour). There was no relationship between MPL concentrations and presence of symptoms or neuroimaging abnormalities. Dopamine agonist treatment had been implemented in 14 patients (27%). Galactorrhoea resolved in all patients (without treatment in 2 cases).
In summary, using this assay, MPL is present in approximately 20% of patients with hyperprolactinaemia. There was no convincing evidence that MPL was responsible for the presenting features, which may have been due to other factors. The neuroimaging abnormalities may also have been incidental findings and it is questionable whether neuroimaging is necessary when macroprolactinaemia is present and the concentration of monomeric PRL is <500mU/L.