Endocrine Abstracts (2006) 11 P616

Rate of change in size of macroprolactinomas with dopamine agonist therapy – is there any relationship to fall in prolactin concentrations?

CL Miller1, A Palalau2, AA Toogood2 & NJL Gittoes2

1Department of Radiology, University Hospitals Birmingham, United Kingdom; 2Division of Medical Sciences, University Hospitals Birmingham, United Kingdom.

The most effective means of treating macroprolactinomas, including those associated with significant visual loss at presentation, is with dopamine agonist (DA) therapy. Improvement in visual function often occurs within days of commencing DA therapy, and usually precedes significant reductions in prolactin (PRL) concentrations and may predate significant evidence of tumour volume reduction by months or years. The temporal association between PRL concentration reductions and tumour volume reduction on DA therapy has been poorly documented. We have made a careful assessment of a contemporary cohort of patients (n=18, 12 female) with macroprolactinomas who were treated with DA therapy to determine rates of change in pituitary tumour dimensions (using sequential MRI) in the context of changes in PRL concentrations. Median (range) follow-up (FU) was 3 (1–9) years. All patients had a precipitous fall in PRL concentrations (median PRL 0.3 (0.01 to 7.6) % of initial PRL at 12/12) with 12 (67%) having normal serum PRL after 12/12; only 1 with a (mildly) raised PRL at 12/12 subsequently normalised PRL over the FU duration. All tumours reduced in size over the FU duration with 91% showing evidence of shrinkage by 12/12. The median (range) change in tumour dimensions at 12/12 were −19 (+7 to −52) % height, −4 (0 to −57) % width, −7 (0 to −53) % A-P; at 24/12 −45 (0 to −76) % height, −16.5 (+5 to −35) % width, −21 (0 to −57) % depth. There was no association between degree of serum PRL reduction and the extent of tumour shrinkage. No regrowth was noted over the FU duration. DA therapy effectively reduces serum PRL concentrations but this does not correlate with reductions in tumour dimensions over 24/12 FU. All macroprolactinomas shrunk to some extent by 24/12 with DA therapy but the rate of change is variable and unpredictable.

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