Background: Several patients with Interstitial Lung Disease show autoimmune characteristics but do not meet the classification criteria for a connective tissue disease. In order to define this condition, the classification of patients with interstitial pneumonia with autoimmune features (IPAF) has been adopted (Fischer’s criteria).

Objectives: To describe the sociodemographic, clinical, functional characteristics and therapeutic management of IPAF in clinical practice and to evaluate the incidence rate of functional respiratory impairment.

Methods: A longitudinal observational study was performed (NEREA registry). Patients diagnosed with IPAF according to Fischer’s criteria were included from ILD diagnosis (Feb 2007 to Dec 2019) and followed until loss of follow-up or Jan 2021. The study was carried out by a multidisciplinary team (pneumologists and rheumatologists) in seven Hospitals of Madrid. The relative functional respiratory impairment, defined as a ≥ 5% decline in percent predicted forced vital capacity (FVC%) compared to the previous visit was set as main outcome. Respiratory function was measured at baseline and every 6-12 months. Covariates included: a) sociodemographic, b) clinical, c) radiological pattern (non-specific interstitial pneumonia [NSIP]; usual interstitial pneumonia [UIP], others); d) FVC% DLCO%; e) laboratory tests; f) therapy used. Survival techniques were used to estimate the incidence rate (IR) of relative functional respiratory impairment, expressed per 100 patient-semester with their respective confidence interval [95 % CI].

Results: 79 IPAF were included, with a follow up of 462.8 patients-semester and a maximum follow-up of 12.3 years. 79% were women with a mean age of 66±11 years. Along with obesity (40%), the most frequent comorbidities at baseline were hypertension, hypercholesterolemia, followed by ischemic heart disease. Baseline FVC% and DLCO% were 88.5±22.7 and 64.2±19.3, respectively. Distribution of IPAF classification criteria was: a) clinical domain: arthritis (46.2%), Raynaud`s phenomenon (35.8%) and mechanic hands (9.3%); b) serological domain: 80.8% positive ANA at >1/320 titer; 29% RF (> 40 IU/ml); 25% positive anti-Ro; c) morphological domain: 46.8% of NSIP and 36.7% of UIP. During the study period, 77.2% of patients (n=61) received treatment: glucocorticosteroids (n=52), mycophenolate (n=25), azathioprine (n=21), rituximab (n=15) and antifibrotics (n=11).

During the follow-up, 50 patients presented 111 relative functional respiratory impairment events over time. The estimated IR was 23.9 [19.9-28.8] per 100 patient-semester, and 50% of the patients developed functional respiratory impairment at 16 months from diagnosis.

IR was similar between patient gender, baseline overall comorbidity, baseline pulmonary functional tests, and age strata, with slight difference in patients >80 years of age. Patients with baseline associated emphysema (IR: 17.6 [10-31]) or without baseline associated fibrosis (IR: 21.1 [15-28]) had lower IR compared to the opposite (IR without emphysema: 24.5[19.3-31]; IR with fibrosis emphysema: 27.5 [19.9-37.9]). As expected, IR was higher in UIP (32.2 [24-42]) compared to NSIP or any other pattern. With respect to serologic markers, patients with ANA titers >=1/320 had a higher IR (26.7 [21-33]) in comparison with those with lower or non-titers of ANA (IR: 15.7 [9.9-25.1]).

Conclusion: In a multicenter registry of Madrid, we have performed a descriptive longitudinal study. IPAF were mostly women in their sixties. The most frequent clinical criteria were arthritis and Raynaud`s phenomenon. An NSIP radiological pattern predominated. At onset, patients have a slightly diminished lung function. The incidence rate of functional deterioration was estimated in 23.9% patient-semester and 50% of the patients developed pulmonary functional deterioration at 16 months from ILD diagnosis. This Incidence rate was higher in patients with an UIP pattern, baseline fibrosis or ANA at medium-high titers.

Disclosure of Interests: None declared