Nonstandard ILD Definitions, Reporting Hinders Estimation of Disease Prevalence

Analyzing accurate global estimates of the incidence and prevalence of interstitial lung disease (ILD) is challenging due to differences in definitions of the disease, diagnostic criteria, and reporting units across geographic regions, according to study findings published in BMJ Open Respiratory Research.

Researchers performed a systematic search of Medline and Embase to determine the incidence and prevalence of ILD between 2015 and 2021, based on evidence from observational studies published in English. Drug-induced ILD reports were excluded, along with case reports, reviews, randomized controlled trials, and conference abstracts. Prevalence was drawn from the general population as well as from single centers.

The reviewers identified 80 observational studies with 88 reported estimates. Half of the reported estimates focused on autoimmune-related ILDs (n=44). Most of the publications were from Asia (n=30, 34.1%) followed by Europe (n=23, 26.1%). Out of the 39 studies covering the incidence of ILD, most were medium risk (n=25) and 2 were high risk. Out of the 78 prevalence assessments, 64.1% were medium risk, 18% were low risk, and 18% were high risk.

The prevalence of Idiopathic pulmonary fibrosis (IPF) ranged from 7 to 1650 per 100,000 persons. The prevalence of systemic sclerosis interstitial lung disease (SSc-ILD) was between 26.1% to 88.1%. Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) ranged from 0.6% to 63.7%. The highest prevalence of SSc-ILD was reported in the Medicare population. The US had the highest prevalence of SSc-ILD, with 19 per 100,000 persons. Canada had the lowest, with 2.3 per 100,000 persons. Researchers noted significant heterogeneity in prevalence with SSc-, RA-, and Rogen’s ILD in different study settings. Incidence was not compared because there was no uniform reporting unit to allow for comparison throughout the study.

Research trends observed during the 6-year period covered by the review included: (1) an increase in the number of studies investigating non-IPF ILDs and autoimmune ILDs; and (2) a 6-fold rise in autoimmune ILDs studies between 2015 and 2021 (3 vs 18 studies, respectively), possibly related to the emergence of antifibrotic therapies for non-IPF fibrosing lung diseases.

A major limitation of this research was the differing diagnostic criteria for ILD in the studies reviewed. Additionally, no meta-analysis was performed; only English-speaking publications were included; and some of the estimates were not generalized.

“There is a fundamental need to standardize ILD diagnosis, disease definitions and reporting to provide the data which will drive the provision of a consistently high level of care for these patients across the globe,” the researchers concluded.

Disclosure: Some study authors declared affiliations with biotech and pharmaceutical companies. Please see the original reference for a full list of authors’ disclosures.