Association of smoking using with ALS risk and prognosis in China

Objectives Cigarette smoking using have been posited as possible risk factors for amyotrophic lateral sclerosis (ALS), but few epidemiological studies supporting this hypothesis in China. We therefore explored the association between smoking with ALS incidence and prognosis in Chinese patients. Design Population-based case-control study. Setting, participants We performed a population-based case-control study in 812 ALS patients and 1500 matched controls. All the objects were recruited from Peking University Third Hospital, from January 2011 to December 2018 throughout China. Outcome measures Demographic data and information about premorbid cigarette smoking habits were collected at the time of diagnosis. The association of smoking with ALS was investigated using logistic regression analysis. Kaplan-Meier curves were used to compare survival time. Cox proportional hazards function and the hazard ratio were used to identify adjusted prognostic predictors. Results Current smokers had an increased risk of ALS (odds ratio = 1.66, 95% confidence interval (CI): 1.46, 1.87) compared to never smokers. Current cigarette pack years ≥20 had a significantly shorter median survival (63.89 months, IQR 55.90–71.87) compared with current cigarette pack years<20 (81.09 months, IQR 77.35–84.84) (p<0.001). Smoking habits were retained in Cox multivariable model. Conclusions Our study has proved current smoking is associated with an increased risk of ALS. Current cigarette pack years ≥20 is an independent negative prognostic factor for survival, with a dose–response gradient. Its influence is irrelevant to the presence ofchronic obstructive pulmonary disease (COPD) or to respiratory status at time of diagnosis. These results can be helpful for understanding and preventing ALS.