Idiopathic pulmonary fibrosis: outcome in relation to smoking status.
BACKGROUND
The pathogenic importance of smoking status in idiopathic pulmonary fibrosis (IPF) is uncertain. In theory, increased oxidative stress in current and former smokers might promote disease progression. However, better survival has been reported for current smokers with IPF, although this might reflect less severe disease at presentation (a "healthy smoker effect").


OBJECTIVE
To determine whether smoking status is associated with survival differences in IPF.


METHODS
A total of 249 patients with IPF were studied (current smokers, n = 20; former smokers, n = 166; never-smokers, n = 63). Survival was evaluated against smoking status, using proportional hazards analysis, adjusting for sex, age, disease severity (extent of the disease on high-resolution computed tomography, composite physiologic index [CPI], percentage predicted diffusing capacity for carbon monoxide in separate models), and the degree of honeycombing.


RESULTS
Current smokers had milder disease than did former smokers, with lower CPI scores (P < 0.0001), less extensive disease on high-resolution computed tomography (P < 0.005), and higher unadjusted survival (hazard ratio = 0.44; 95% confidence interval = 0.24, 0.80; P = 0.007). However, survival did not differ between current and former smokers (P = 0.39) after adjustment for CPI levels. By contrast, the increase in survival seen in nonsmokers than in former smokers (hazard ratio = 0.51; 95% confidence interval = 0.41, 0.83; P = 0.008) was amplified (P < 0.0005) by adjustment for CPI levels.


CONCLUSIONS
In IPF, survival and severity-adjusted survival are higher in nonsmokers than in former smokers or the combined group of former and current smokers. By contrast, a better outcome in current smokers, compared with former smokers, reflects less severe disease at presentation and may represent a healthy smoker effect.
Antoniou
Katerina M
KM
Interstitial Lung Disease Unit, c/o Emmanuel Kaye Building, Manresa Road, London SW3 6LR, UK.
Hansell
David M
DM
Rubens
Michael B
MB
Marten
Katharina
K
Desai
Sujal R
SR
Siafakas
Nikolaos M
NM
Nicholson
Andrew G
AG
du Bois
Roland M
RM
Wells
Athol U
AU
D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011658:Pulmonary Fibrosis / Q000209:etiology / Q000401:mortality* / Q000503:physiopathology; D012720:Severity of Illness Index; D012907:Smoking / Q000009:adverse effects*; D016019:Survival Analysis; D014797:Vital Capacity