Endocrine Abstracts

Differentiation between non functioning pituitary macroadenomas (NFPA) and prolactinomas may be difficult as hyperprolactinaemia can also be present at diagnosis in NFPA cases due to pituitary stalk compression (disconnection hyperprolactinaemia). Some authors suggested that prolactin >2,000 mIU/l is almost diagnostic of a prolactinoma, while others use a higher cut-off of >5000 mIU/l. Our aim was to identify the level of prolactin above which a prolactinoma was more likely than NFPA.

We identified from computerised hospital and neurosurgical records 140 patients who underwent surgery for histologically-proven NFPAs and who had prolactin measurement available prior to surgery. Macroprolactin was measured in those with prolactin of >800 mIU/l in approximately two thirds of patients.

Hyperprolactinaemia was present in 62.1% of patients. Of these patients the median (range) prolactin was 618 (314–2738) mIU/l. Of the 84 males, 58.3% had hyperprolactinaemia, with a median prolactin of 483.5 (314–1289) mIU/l. Elevated serum prolactin was present in 68.4% of the 57 females, with median prolactin of 893 (536–2738) mIU/l.

There were 5 patients with a prolactin >2000 mIU/l. One had hypermacroprolactinaemia and two patients were pregnant. Of the 2 remaining patients, one had a prolactin of 2810 mIU/l which fell to 2040 mIU/l after subtraction of macroprolactin. The final patient had a prolactin of 2380 mIU/l, but macroprolactin was not measured.

Our findings are in agreement with a recently published large series¹, and suggest that prolactin >2000 mIU/l is rare in patients presenting with a NFPA, and such patients should routinely be considered for a trial of dopamine agonist therapy.

Reference

1. Karavitaki N, Thanabalasingham G, Shore HCA, Trifanescu R, Ansorge O, Meston N, Turner HE, Wass JAH. Do the limits of serum prolactin in disconnection hyperprolactinaemia need re-definition? A study of 226 patients with histologically verified non-functioning pituitary macroadenoma. Clin Endocrinol 2006 65 524–529.