Endocrine Abstracts

Background: Acromegaly is a rare condition characterised primarily by tumourous production of excess Growth Hormone (GH) from a pituitary adenoma. The Octreotide Challenge Test (OCT) has been used in the RVI to predict short term efficacy of long-acting Somatostatin Analogue (SSA) therapy.

Aims: We retrospectively reviewed the OCT results of all patients with acromegaly treated at RVI from 2005 to 2021 to evaluate its clinical utility.

Methods: OCT protocol: blood sampling for GH is undertaken at baseline and then hourly for 6 h after SC administration of 100 mg of short-acting Octreotide. Data extracted: patient demographics, baseline GH and nadir GH on OCT, IGF1 level at presentation and after long-acting SSA therapy, follow-up MRI findings after SSA therapy.

Results: 46/79 patients diagnosed with acromegaly had OCT. Female to male ratio was 3:2, with a mean age of 49 years and mean IGF1 of 3xULN at diagnosis. All patients demonstrated a reduction in GH on OCT, with a mean reduction of 72%. 25 patients received SSA pre-surgery or as long-term medical therapy. There was no relationship between reduction of GH on OCT and IGF1 suppression on SSA. Females were more likely to experience >50% reduction in IGF1 on SSA compared to males (78% vs. 56%, P=0.04). 18 patients underwent repeat imaging >6 months after SSA initiation and/or before surgery. Tumour shrinkage were demonstrated in 67% of cases. Shrinkage was most likely to be observed in females (66% vs. 33%, P<0.05). Average GH reduction on OCT was 68% in patients who demonstrated tumour shrinkage compared to 83% in those who did not (P<0.05).

Conclusions: OCT does not predict biochemical response to SSA therapy in our cohort. Female patients are more likely to have a better reduction in IGF1 and tumour shrinkage on SSA therapy compared to males. Tumour shrinkage is inversely related to GH reduction on OCT in our cohort.