Abstract
Some patients with interstitial lung diseases (ILDs) other than idiopathic pulmonary fibrosis exhibit a progressive clinical phenotype. These chronic progressive fibrosing ILDs have a variety of underlying diseases, and their prevalence is currently unknown. Here we carry out the first systematic review of literature on the prevalence of fibrosing ILDs and progressive fibrosing ILDs using data from physician surveys to estimate frequency of progression among different ILDs. We searched MEDLINE and Embase for studies assessing prevalence of ILD, individual ILDs associated with fibrosis and progressive fibrosing ILDs. These were combined with data from previously published physician surveys to obtain prevalence estimates of each chronic fibrosing ILD with a progressive phenotype and of progressive fibrosing ILDs overall. We identified 16 publications, including five reporting overall ILD prevalence, estimated at 6.3-76.0 per 100,000 people in Europe (four studies) and 74.3 per 100,000 in the USA (one study). In total, 13-40% of ILDs were estimated to develop a progressive fibrosing phenotype, with overall prevalence estimates for progressive fibrosing ILDs of 2.2-20.0 per 100,000 in Europe and 28.0 per 100,000 in the USA. Prevalence estimates for individual progressive fibrosing ILDs varied up to 16.7 per 100,000 people. These conditions represent a sizeable fraction of chronic respiratory disorders and have a high unmet need.