Fig. 2
Forrest plot of the result of univariate analysis for smoking history (ever-smoking) as a risk factor. The result of univariate analysis in three studies was pooled for meta-analysis. Smoking history (ever-smoking) was not significantly associated with the development of acute exacerbation (AE) of systemic autoimmune disease-associated interstitial lung disease (ILD) with a hazard ratio (HR) of 1.22 (95% confidence interval: 0.57–2.60, p = 0.61/95% prediction interval: 0.0004–3734.1). There was considerable heterogeneity (chi2 = 4.61, p = 0.10, I2 = 57%). Although both Cao 2019 and Suda 2009 enrolled systemic autoimmune disease-ILDs, the former study demonstrated that Sjögren’s syndrome was the largest in number as the underlying disease of AE whereas it was rheumatoid arthritis (RA) in the latter study. Hozumi 2013 only enrolled RA-ILD cases