Endocrine Abstracts

Introduction

Pituitary macroadenoma requires extensive endocrine investigations to diagnose any evidence of hormone excess or deficiency. As a part of routine investigation, IGF-1 is frequently used to exclude growth hormone excess. Here we report 3 cases of pituitary macroadenoma, who had a normal pre-operative IGF-1 but post-operatively developed biochemical evidence of growth hormone excess.

Cases

We report 3 female patients who presented with visual field defects. They were 19, 22 and 27 years at presentation. Initial investigations revealed normal pituitary function in all. IGF-I levels were respectively 22.9, 67.4 and 22.9 nmol/l (normal range 23-70). Pituitary MRI scan revealed macroadenoma involving the optic chiasma in all 3 patients, who then underwent transphenoidal pituitary surgery.

Histology confirmed GH and prolactin positive adenomata in 2 cases and a sparsely granulated somatotroph adenoma in one case. Post-operative endocrine evaluation showed a progressive rise in IGF-1 levels. This led to a formal dynamic growth hormone assessment (oral glucose tolerance test with GH measurement), which confirmed GH excess in all 3 patients. None of them had any physical signs of acromegaly. One had post-operative radiotherapy; the other two are on Somatostatin analogue therapy to control their GH levels.

Discussion

IGF-1 is commonly used as a screening test for acromegaly. There are some instances where we should exercise some caution in interpreting the results. All 3 women were on oral contraceptive pills (OCP). It has been reported that exogenous oestrogen lowers circulating levels of IGF-I. Following surgery, none were taking the OCP, which may have unmasked a high IGF-1 level.

Learning points

IGF-1 itself is not always reliable in diagnosing growth hormone excess, particularly in women taking oestrogen in some form. We suggest that in all cases of pituitary macroadenoma, formal growth hormone estimation along with IGF-I may increase the sensitivity for detection of growth hormone excess.