Many factors contribute to the survival and prognosis of patients diagnosed with hypersensitivity pneumonitis (HP). Prognosis varies depending on the patient’s overall health and the severity of their disease progression.1 Patients with relatively mild HP can stabilize and even recover, while some with more severe HP progressively decline, ultimately leading to respiratory failure and death. Patients with nonfibrotic HP tend to have a more favorable prognosis than those with fibrotic HP, particularly those with a usual interstitial pneumonia (UIP)-like pattern.
One study following 142 patients with HP from 1982-2008 reported that the rate of mortality was significantly higher among those who were older (median age 61 vs 54), had lower total lung capacity (77% vs 89%), diffusing capacity of the lung for carbon monoxide (DLCO)(54% vs 58%), had worse dyspnea (American Thoracic Society [ATS] dyspnea score 10 vs 7, with a higher score meaning more severe dyspnea), and were more likely to have fibrosis (75% mortality of those with fibrotic HP, 45% for those with nonfibrotic HP).2 Mean survival was 4.9 years for those with fibrotic HP compared to 16.9 years for those with nonfibrotic HP. Identification of an inciting antigen also improved survivability, with 39% mortality among those with an identified inciting antigen compared to 72% for those without, and a median survival of 18.2 years vs 9.3 years.
A retrospective study of 101 patients with HP over a median of 4.6 years found that older age, lower lung function, and higher levels of fibrosis seen on HRCT were associated with an increased mortality rate.3 Forced vital capacity was 66.6% in non-survivors vs 79.2% in survivors, DLCO was 55.4% vs 63.4%, and total lung capacity was 66.9% vs 76.1%. Higher levels of reticulation (16.2% in non-survivors vs 11.6% in survivors), honeycombing (1.7% vs 0.5%), fibrosis (20.9% vs 12.1%), mosaic attenuation (17.3% vs 9.4%), and presence of a UIP-like pattern (66.7% among non-survivors vs 47.5%) seen on HRCT imaging were also associated with higher mortality rates. Patients who had a higher fibrosis score (≥12.0%) had a worse prognosis compared to those with a low fibrosis score (146.7 months vs. 58.3 months, respectively).
An insurance claims-based population analysis in the United States found that between 2004-2013, there were 4,474 incident HP cases, 1,834 of which had vital status data.4 After about four years, mortality rates were 20% for HP, 22% for chronic HP, and 28% for fibrotic HP. After about seven years, mortality rates were 29% for HP, 31% for chronic HP, and 42% for fibrotic HP. Mortality rates increased with age, with patients 65 and older having the highest mortality rates (115.9 per 1,000 person-years vs 37.5 for those aged 55-64, 16.0 for 45-54, 3.3 for 35-44, and 9.3 for 25-34).
A longitudinal observational study using the Danish National Patient Registry from 1998-2010 found a significant association between older age and mortality.5 Of the 753 patients identified with HP and 3,012 matched controls, those 60-69 years old had 19.4% mortality compared to 13.7% control, patients 70-79 had 46.3% mortality vs 29.1% control, and patients ≥80 had 63.2% mortality vs 43.4% control.
Another study investigated the role of radiologic phenotypes in understanding the prognosis and survival time of 117 patients with HP.6 Honeycombing was associated with the shortest median survival (2.8 years), while those with non-honeycomb fibrosis but without honeycombing had a median survival of 7.95 years. Patients without any fibrosis or honeycombing had the greatest survival (>14.7 years). These findings suggest that distinguishing between honeycombing and non-honeycomb fibrosis is important in understanding prognosis.
Comorbidities associated with HP, such as autoimmune diseases, can affect survival.7 A study of 120 patients with chronic fibrotic HP analyzed how autoimmune factors could contribute to survival outside of antigen avoidance. Of these 120 patients, nine had a diagnosed autoimmune disease (scleroderma, Sjogren’s disease, rheumatoid arthritis, systemic lupus erythematosus, ulcerative colitis, and idiopathic inflammatory myopathy), and nine had features of autoimmunity (defined as symptoms and serology consistent with connective tissue disease). Having an autoimmune disorder or symptoms was associated with lower mean survival (16.5 months vs 29.7 months).
Another study evaluated the relationship between chronic HP and pulmonary hypertension in a cohort of 120 patients over five years.8 Having pulmonary hypertension was associated with a lower survival (23 months) compared to patients without it (98 months).
References
- Raghu G, Remy-Jardin M, Ryerson CJ, et al. Diagnosis of Hypersensitivity Pneumonitis in Adults. An Official ATS/JRS/ALAT Clinical Practice Guideline. Am J Respir Crit Care Med. Aug 1 2020;202(3):e36-e69. doi:10.1164/rccm.202005-2032ST
- Fernández Pérez ER, Swigris JJ, Forssén AV, et al. Identifying an inciting antigen is associated with improved survival in patients with chronic hypersensitivity pneumonitis. Chest. Nov 2013;144(5):1644-1651. doi:10.1378/chest.12-2685
- Oh JH, Kang J, Song JW. Fibrosis score predicts mortality in patients with fibrotic hypersensitivity pneumonitis. Front Med (Lausanne). 2023;10:1131070. doi:10.3389/fmed.2023.1131070
- Fernández Pérez ER, Kong AM, Raimundo K, Koelsch TL, Kulkarni R, Cole AL. Epidemiology of Hypersensitivity Pneumonitis among an Insured Population in the United States: A Claims-based Cohort Analysis. Annals of the American Thoracic Society. 2018;15(4):460-469. doi:10.1513/AnnalsATS.201704-288OC
- Rittig AH, Hilberg O, Ibsen R, Løkke A. Incidence, comorbidity and survival rate of hypersensitivity pneumonitis: a national population-based study. ERJ Open Research. 2019;5(4)doi:10.1183/23120541.00259-2018
- Salisbury ML, Gu T, Murray S, et al. Hypersensitivity Pneumonitis. Chest. 2019;155(4):699-711. doi:10.1016/j.chest.2018.08.1076
- Adegunsoye A, Oldham JM, Demchuk C, Montner S, Vij R, Strek ME. Predictors of survival in coexistent hypersensitivity pneumonitis with autoimmune features. Respiratory Medicine. 2016;114:53-60. doi:10.1016/j.rmed.2016.03.012
- Koschel DS, Cardoso C, Wiedemann B, Höffken G, Halank M. Pulmonary Hypertension in Chronic Hypersensitivity Pneumonitis. Lung. 2012;190(3):295-302. doi:10.1007/s00408-011-9361-9
