What is the Clinical Relevance of Macroprolactinaemia? A Clinical Case Report
JG Boyle & AR McLellan
The clinical relevance of macroprolactin and its prevalence among those with 'hyperprolactinaemia' are unclear(1). Macroprolactinaemia has often been described as asymptomatic, benign and not related to pituitary disease(2,3,4). Recent reports, however, suggest that macroprolactinaemia is common among those with 'hyperprolactinaemia', can often be symptomatic and may be occasionally associated with pituitary adenoma(5,6). Pituitary imaging has been recommended in all symptomatic patients. We report a case a macroprolactinaemia in association with a potentially sight threatening pituitary macroadenoma. Forty year old woman with an eight month history of secondary amennorhoea(K=X/7). Periods were normal until aged thirty-nine years. No galactorrhoea, headache or visual upset. Pregnancy excluded. Drug therapy: nil. Examination unremarkable. Investigations:Total prolactin range 2140-4174mu/L and average 3206mu/L(Bayer immuno 1). PEG precipitation was 35.8%. Monomeric prolactin 1190mu/l(total 2760mu/L. LH and FSH were 4 and 6.3 U/L respectively. Oestradiol was undetectable. fT4 was 15pmol/l and TSH was 1.6mu/L. Cranial MRI revealed generalised enlargemnt of the pituitary with the superior aspect in contact with the chiasm . The tumour was two centimetres in diameter with an area of cystic change. Cabergoline(0.25mg weekly)was commenced and formal perimetry is awaited. The average prolactin falls short of the textbook levels of prolactin expected for a prolactinoma. Nevertheless prolactinoma remains a possibility. We cannot exclude a non functioning pituitary adenoma with stalk disconnection. The response to dopamine agonist therapy is awaited but may be limited by the degree of cystic change. This report supports the association between macroprolactinaemia and macroadenoma. It reinforces the message that macroprolactinaema cannot be dismissed as a mere biochmical artefact, at least among symptomatic patients. Further investigation in the form of pituitary imaging is recommended in such patients and in this particular case may be of prognostic importance.