Global Cushing's disease epidemiology: a systematic review and meta-analysis of observational studies

Cushing's disease (CD), 70% of endogenous hypercortisolism cases, is a rare disease caused by adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. To date, no systematic reviews and meta-analyses on its global epidemiology have been published. We provide a systematic review and meta-analysis of CD global epidemiology, also evaluating the quality of study reporting for the identified studies.

MEDLINE and EMBASE databases were searched for studies on CD epidemiology from inception until November 30th, 2020, including original observational studies in English about CD prevalence and/or incidence for well-defined geographic areas. Two reviewers independently extracted data and assessed reporting quality. CD prevalence/incidence pooled estimates were derived from a random-effects meta-analysis. Reporting quality was assessed using a STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) checklist adapted for observational studies on rare diseases, heterogeneity using the Cochran's Q-test and its derived measure of inconsistency (I²).

Thirteen studies were included. The pooled CD prevalence was 2.2 [95% CI 1.1-4.8] per 100,000, while the incidence rate was 0.24 [95% CI 0.15-0.33] per 100,000 person-years. For both parameters, considerable between-studies heterogeneity was found (I² = 78.8% and 87.8%, respectively). The quality of study reporting was rated as medium for 11 (84.6%) studies and as low for 2 (15.4%).

Overall, our systematic meta-analysis demonstrated CD epidemiology to be similarly reported across different areas of the world, with some exceptions regarding regional differences or observation period intervals. Keeping into account the methodological differences between each paper, large-scale studies on CD epidemiology are warranted. Setting up national specific registries, based on standardized diagnostic and clinical parameters, with clearly defined selection and analysis criteria, and a strong cooperation between the scientific national societies for endocrinology is crucial to exclude other causes of variability (i.e. geographical differences due to other factors like (epi)genetic changes), and to support public health decision making.