by Elena Moro
For December 2015 we have selected: Ramanujam R, Hedstrom A-K, Manouchehrinia A, et al. Effect of smoking cessation on multiple sclerosis prognosis. JAMA Neurol 2015; 72(10):1117-1123.
The usual course of multiple sclerosis (MS) is characterized by the conversion to secondary progressive disease within about 20 years from the first attack. Great efforts are currently made to modify the disease progression with the use of aggressive and expensive medical treatments. Furthermore, management of risk factors associated with the disease is another important therapeutic approach. Cigarette smoking is known to be a risk factor for developing MS and in disease progression, but the real impact of continued smoking after the diagnosis has not been fully investigated.
This study focuses on the role of smoking continuation or cessation on the conversion time to secondary progressive MS after the diagnosis. Data were collected from individuals participating to the Genes and Environment in Multiple Sclerosis (GEMS) Study, a population-based case-controlled study including patients from the Swedish National MS Registry. From this database 2,358 patients with relapsing-remitting and secondary progressive MS were enrolled in the study. A questionnaire about data on smoking habits (year interval of beginning and ending, and number of cigarettes per day or week) was retrospectively administered. There were 1,012 patients who never smoked, 618 who were past smokers, and 728 patients who smoked at time of diagnosis (of whom 216 converted to secondary progressive MS). The analysis focused on the latter group of patients, considering the time to secondary progressive disease conversion by using an accelerated failure time (AFT) model. In this survival model, the year of MS diagnosis was considered as the study entry point, with smoking as a time-varying covariate. Sex, age at diagnosis, snuff use, and smoking before the diagnosis were also analyzed as covariates. Kaplan-Meier plots were also used. Of the 728 smokers at diagnosis, 118 stopped smoking the year after diagnosis, 332 continued, and 278 smoked intermittently. The AFT model showed that each additional year of smoking after diagnosis accelerated the conversion time to secondary progressive MS by 4.7% (acceleration factor, 1.047; 95% CI, 1,.023-1.072; P<.001). Age at diagnosis was also significantly associated with time to conversion (P<.001). Kaplan-Meier plots also indicated that continuer smokers converted to secondary progressive MS faster than quitters (at age 48 and 56 years, respectively).
“This study indicates that continuous smoking after MS diagnosis accelerates the time to conversion to secondary progressive disease. Continuer smokers converted about 8 years earlier compared to those who quitted smoking.” says Prof. M. Clanet, Department of Neurology, CHU Toulouse, France. “Smoking is the only risk factor for MS found to be associated with disease outcome (none of the more than 150 genetic risk factors have been associated with MS severity). Smoking seems to alter the autoimmune response and might also be associated with the effectiveness of treatment.”
“This study has several limitations, including the retrospective nature of the questionnaire and the presence of other potential confounders, such as un-observed variables associated with smoking”, says Prof. M. Hutchinson, Department of Neurology, St. Vincent’s University Hospital, University College of Dublin, Ireland. “However, this paper is of considerable importance. The authors have convincingly shown that quitting smoking following the diagnosis of MS improved outcomes. While we had known already that smoking increased the risk of MS and patients who smoked appeared to do worse in the longer term, these data are really important in that they show that quitting smoking, even after diagnosis, is a very important modifiable environmental risk factor. As the authors point out, this intervention, stopping smoking, is considerably cheaper and more effective than many of the disease modifying therapies currently in widespread use. We must use these data in the clinic to persuade our patients (early in the course of the disease) of the importance of stopping smoking in order to delay the entry to the secondary progressive stage of MS. “
