Objective: To compare the survival outcomes between myositis-associated usual interstitial pneumonia (MA-UIP) and idiopathic pulmonary fibrosis (IPF-UIP).
Methods: Adult MA-UIP and IPF-UIP patients were identified using CTD and IPF registries. The MA-UIP cohort included myositis or anti-synthetase syndrome patients with interstitial lung disease while manifesting UIP on high-resolution CT chest and/or a lung biopsy revealing UIP histology. IPF subjects met American Thoracic Society criteria and similarly had UIP histopathology. Kaplan-Meier survival curves compared cumulative and pulmonary event-free survival (event = transplant or death) between (i) all MA-UIP and IPF-UIP subjects, (ii) MA-UIP with biopsy proven UIP (n = 25) vs IPF-UIP subjects matched for age, gender and baseline forced vital capacity (±10%). Cox proportional hazards ratios compared the survival controlling for co-variates.
Results: Eighty-one IPF-UIP and 43 MA-UIP subjects were identified. The median cumulative and event-free survival time in IPF vs MA-UIP was 5.25/1.8 years vs 16.2/10.8 years, respectively. Cumulative and event-free survival was significantly worse in IPF-UIP vs MA-UIP [hazards ratio of IPF-UIP was 2.9 (95% CI: 1.5, 5.6) and 5.0 (95% CI: 2.8, 8.7) (P < 0.001), respectively]. IPF-UIP event-free survival (but not cumulative) remained significantly worse than MA-UIP with a hazards ratio of 6.4 (95% CI: 3.0, 13.8) after controlling for age at interstitial lung disease diagnosis, gender, ethnicity and baseline forced vital capacity%. Respiratory failure was the most common cause of death in both groups. A sub-analysis of 25 biopsy-proven MA-UIP subjects showed similar results.
Conclusion: MA-UIP patients demonstrated a significant survival advantage over a matched IPF cohort, suggesting that despite similar histological and radiographic findings at presentation, the prognosis of MA-UIP is superior to that of IPF-UIP.
Keywords: anti-synthetase syndrome; idiopathic pulmonary fibrosis (IPF); interstitial lung disease (ILD); myositis; prognosis; survival; usual interstitial pneumonia (UIP).
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