Progression and prognosis of interstitial pneumonia with autoimmune features: a longitudinal, prospective, multi-centre study.

To evaluate the rate of progression towards specific autoimmune diseases (SADs) of a prospective, multi-centre cohort of patients classifiable as interstitial pneumonia with autoimmune features (IPAF). IPAF patients were enrolled based on specific research criteria, and jointly followed by rheumatologists and pulmonologists for at least one year with clinical check-ups, serological exams including autoimmunity, capillaroscopy and high-resolution computed tomography (HRCT). Diagnostic assessment was repeated at least once a year, or earlier when deemed useful. We enrolled 191 IPAF patients through 95 different combinations of IPAF criteria. Of these, 24.1% progressed towards SAD, mainly in connective tissue diseases but also in microscopic polyangiitis. The IPAF patients who progressed were younger than stable IPAF patients (63±10 years vs. 68±9 years, p=0.002) and had a longer follow-up (36.9±18.7 vs. 29.3±15.7 months, p=0.007), but similar severity. No parameters were associated with overall progression, but some parameters were associated with the development of specific diagnoses: Sjögren's syndrome with positivity for SSA (p=0.007, χ2 7.4); idiopathic inflammatory myopathy with mechanic's hands (p=<0.0001, χ2 12.6), organizing pneumonia pattern (p=0.01, χ2 6.1), positivity for anti-Pm/scl (p=0.04 χ2 4.1) and anti-MDA5 (p=0.04, χ2 4.2); systemic sclerosis with palmar telangiectasias (p=<0.0001 2 18.3), positivity for anti-Scl70 (p=<0.0001 χ2 12.5) and anti-PM/Scl (p=0.001 χ2 10.1). IPAF patients had a rate of progression towards SAD similar to that reported in previous studies on undifferentiated connective tissue diseases, thus including some patients in which lung involvement could represent the first or even the sole clinical manifestation of a SAD.