Exploring the Role of Autoimmune Conditions in Acute Interstitial Pneumonia

Clinical factors influencing outcomes of patients hospitalized with acute interstitial pneumonia (AIP) are not well described because of the condition's rarity.

Do patients with AIP and autoimmune conditions differ from patients with AIP without autoimmune conditions in mortality, recurrence, mechanical ventilation, discharge disposition, and length of hospital stay?

This retrospective cohort study used US MarketScan and Medicare claims (2016-2023). Diagnoses were identified using International Classification of Diseases, 10th Revision, codes. Outcomes included in-hospital, 90-day, and 180-day mortality (Medicare only); AIP recurrence; mechanical ventilation within 30 days; discharge disposition; and length of stay. Multivariable logistic and negative binomial regression compared outcomes by autoimmune status, adjusting for demographics and geography.

The study included 4,726 patients from Medicare claims and 975 patients from MarketScan claims; 20% had an autoimmune condition. Patients with autoimmune conditions covered by Medicare showed a significantly lower odds of 90-day mortality (OR, 0.85; 95% CI, 0.74-0.99), higher odds of discharge home (OR, 1.18; 95% CI, 1.02-1.36), and lower odds of discharge to a skilled nursing facility (OR, 0.77; 95% CI, 0.61-0.97). Length of stay, recurrence, mechanical ventilation, and results from MarketScan did not differ significantly by autoimmune status.

Our results show that patients with AIP and autoimmune conditions covered by Medicare experienced lower 90-day mortality and more favorable discharge disposition, and other outcomes were similar. These differences may reflect a subgroup characterized by greater engagement with specialty care and differential treatment approaches. Future work is needed to identify factors associated with better AIP outcomes to inform more effective care.