Background: Interstitial lung diseases (ILD) are a diverse group of pulmonary diseases for which accurate diagnosis is critical for optimal management and outcomes. ILD is typically associated with impairment in forced vital capacity (FVC) and carbon monoxide diffusion capacity (DLCO). The greatest loss of Pulmonary function tends to occur early in the course of the disease but the natural history of ILD is variable. FVC decline has been used as the primary endpoint in several studies and NICE England recently approved antifibrotic treatment based on this endpoint. A greater than 10% decline in FVC has been reliably correlated with poorer outcome and recent evidence-based guidelines recommend that an absolute decrease in FVC of 10% can be used as a surrogate marker of mortality. Diagnosing ILD, has become critically important, as patients with ILD can now potentially be treated with new antifibrotic therapies.

Objectives: Our aim was to obtain insights into the rate of decline in Pulmonary function in all subtypes of ILD in our cohort. We investigated whether baseline patient characteristics including age, smoking history, sex, body mass index (BMI), comorbidities including Gastro-oesophageal reflux disease (GORD) and OSA influenced the trajectories’ Pulmonary function

Methods: This is a retrospective observational study from a single centre, Southend University Hospital, England UK. Patients were identified from local ILD MDT from January 2016 until December 2023. We collected data on the demographics, occupation, age at ILD onset, smoking status, imaging, blood tests including autoimmune serology, MDT recommendations, change in diagnosis after MDT, tertiary referral, serial PFTs, medications and outcomes. We compared FVC and DLCO at baseline and at 52 weeks in all subtypes of ILD and the risk factors for decline

Results: Data from 195 consecutive patients were included. Mean age of the cohort at diagnosis was 74 years. 115 were men (59%) and 80 were women (41%). 126 (65%) were current or ex-smokers. Mean duration of ILD was 40 months (2–168 months). 122 (62.5%) have died at the time of the study; 73/122 (60%) directly or secondary to complications of ILD. We included most common subtypes in the analysis: Idiopathic Pulmonary Fibrosis (IPF)=64, RA-ILD =23, Hypersensitivity Pneumonitis (HP)=17, Interstitial Pneumonia with Autoimmune Features (IPAF)=9, unclassified=32, SSc-ILD=11, vasculitis=4, Sjogren’s=2, myositis=1 and sarcoidosis=6. For analysis, we included RA, SSc, vasculitis, Sjogren’s, myositis, and sarcoidosis in the CTD-ILD group. 23 were excluded from the analysis (COOP, OP, CPFE, PPFE and drug induced pneumonitis).

We defined FVC decline greater than 10% as severe disease progression and it was observed in: 5/47 in CTD-ILD, 1/9 in IPAF, 5/17 in HP, 5/32 in unclassified and 13/64 in IPF. Moderate disease progression was defined as FVC decline between 5-10% and it was observed in: 4/47 in CTD -ILD, 2/17 in HP, 2/32 in unclassified and 6/64 in IPF. DLCO>10% at 52 weeks were as follows: 1/32 in unclassified, 5/64 in IPF, 1/9 in IPAF, 3/17 in HP, 9/47 in CTD-ILD. In multivariate analysis, male gender (p=0.044), GORD were the predictors for FVC decline. Only, high BMI (p=0.006) was associated with DLCO decline.

Conclusion: The rate of decline in lung function during follow-up differed across subgroups. We identified male gender and GORD as the poor predictors for decline in FVC and high BMI for decline in DLCO. These data support the unpredictable progressive nature of ILD.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: None declared.