Prognosis of Equivocal Interstitial Lung Abnormalities in a Health Check-up Population.

Rationale: Equivocal interstitial lung abnormality (ILA) involves less than 5% of any lung zone or presents unilaterally without satisfying the diagnostic criteria for ILA; however, the prevalence and prognosis of equivocal ILA are unknown.

Objectives: To investigate the prevalence and long-term prognosis of equivocal ILA.

Methods: This retrospective cohort study included individuals who underwent chest CT as part of a health check-up program in 2010 at St. Luke's International Hospital in Tokyo, Japan. ILA and equivocal ILA were diagnosed using the Fleischner Society criteria. The primary outcome was the annual rate of forced vital capacity (FVC) decline in the ILA, Equivocal ILA, and No ILA groups, evaluated using a mixed-effects model. Radiological progression was also evaluated.

Results: Among the 20,896 individuals included in the study, ILA and equivocal ILA were present in 2.0% (95% CI: 1.8-2.2%) and 0.4% (95% CI: 0.4-0.5%) of individuals, respectively. Follow-up pulmonary function tests were available for 18,101 (87%) individuals, with a median follow-up time of 8.3 (interquartile range: 4.0-9.0) years. Individuals with equivocal ILA showed a significantly greater rate of FVC decline than those without ILA (-36.7 vs. -27.7 mL/year, P = 0.008). Of the 86 individuals with equivocal ILA, 20 (23%) exhibited progression during the follow-up period; of these, 19 progressed to definite ILA.

Conclusions: Individuals with equivocal ILA showed a significant tendency for FVC decline compared to those without ILA. A considerable number of cases progressed to definite ILA, warranting careful attention. Clinicians should be aware that even mild interstitial changes that do not meet the current criteria for ILA may deteriorate.