An analysis of incidence and characteristics of Cushing's syndrome in Malta : a population based study

Abstract

AIM: There are few reports discussing incidence and characteristics of the whole group of Cushing’s syndrome patients in the literature. The aim was to establish the incidence of endogenous Cushing’s syndrome with in-depth analysis of their various subtypes in a well-defined population.

METHODS: Retrospective cross-sectional analysis of Cushing’s syndrome patients diagnosed between 2008 and 2017. A thorough search for patients was carried out in the central hospital registries including outpatients departments, surgical registries, radiological department and specialty clinic databases.

RESULTS: 26 patients were identified as diagnosed with Cushing’s syndrome over the 10-year period equating to a standardised incidence rate (SIR) of 4.7/1,000,000/yr with an almost equal SIR among males and females. Analysing the various subtypes of Cushing’s syndrome, the majority (n = 13) were due to an ACTH secreting pituitary adenoma (SIR 2.5/1,000,000/yr). In this subtype males had a SIR of 3.4/1,000,000/yr compared to 1.7/1,000,000/yr in females. ACTH independent Cushing’s had a SIR of 1.8/1,000,000/yr with a strong female predominance (9:1) (SIR females: 3.0/1,000,000/yr; males: 0.5/1,000,000/yr). The SIR of ectopic ACTH secreting tumours was 0.4/1,000,000/yr. Interestingly hypokalaemia was present at diagnosis in those patients who harboured malignant causes for their Cushing’s syndrome (ectopic ACTH secreting tumours or adrenocortical carcinomas) and had markedly elevated cortisol levels at baseline compared to the rest (P < 0.001). Mean cortisol post overnight dexamethasone suppression testwas 1714 nmol/l (± 692 S.D.) in the malignant patients and 522 nmol/l (± 288 s.d.) in those patients with a benign tumour (P = 0.004). Mean ACTH values for Cushing’s disease patients was 110.4 (± 77.2 SD) pg/ml while in the ACTH independent group it was 5.5 (± 4.7 S.D.) pg/ml (P < 0.001).

CONCLUSION: Cushing’s syndrome is a rare disease. Although the numbers are small, we could still establish distinct characteristics in the different subtypes.