Endocrine Abstracts

Introduction: The 2022 WHO classification identifies seven different pituitary tumour subtypes with growth hormone (GH) secretion and/or expression, with or without concurrent prolactin expression. The response to dopamine agonist (DA) treatment in these subtypes requires further investigation. The bromocriptine test has historically been a part of the acromegaly evaluation and may provide insights to DA treatment responsiveness. We aimed to explore the correlations between baseline serum-prolactin concentrations, bromocriptine test response and radiological features in patients with acromegaly to formulate hypotheses for future histological, molecular and clinical studies.

Material and methods: We included patients diagnosed with acromegaly from 2008 to 2017 who underwent a bromocriptine test (2.5 mg). The test was considered positive if the GH levels declined by >50% at 2, 4 or 6 hours (nadir value) after bromocriptine administration. We correlated baseline serum-hormone concentrations and MR images at diagnosis with test responses. Assessment of MR images included tumour size and volume, invasiveness based on the KNOSP criteria, T1 and T2 intensity and visual assessment of pituitary stalk affection (stalk deviation, dislocation or no visible stalk due to large tumour size).

Results: The study comprised 60 patients (34 males, 26 females) with a median age of 45 years (IQR 34-56). Thirty-five (58%) had a positive and 25 (42%) had a negative bromocriptine test. We found a significant correlation between baseline prolactin above upper reference limit and a positive bromocriptine test (P=0.02). The positive test result group also had a significantly higher median baseline prolactin compared to the negative test result group (382 mU/l (IQR 254-727) vs 224 mU/l (IQR 181-475), P=0.03). Further, there was a correlation between a positive test and lower invasiveness (KNOSP) (P=0.02). There were no significant differences between pituitary stalk affection and test results or prolactin levels.

Conclusions: Patients with >50% GH decline after a 2.5 mg bromocriptine dose had higher baseline serum-prolactin and less tumour invasiveness. Future studies are warranted to evaluate the association between the bromocriptine test, markers of tumour aggressiveness and treatment response.