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BRIEF COMMUNICATIONS: Trond Riise, Monica W. Nortvedt, and Alberto Ascherio Smoking is a risk factor for multiple sclerosis Neurology 2003; 61: 1122-1124 [Abstract] [Full text] [PDF]

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Smoking is a risk factor for multiple sclerosis

Iftah Biran, Israel Steiner   (19 February 2004)

Reply to Biran et al

Trond Riise, Monica W. Nortvedt, and Alberto Ascherio   (19 February 2004)

Smoking is a risk factor for multiple sclerosis 19 February 2004
Iftah Biran, Hadassah University Medical Center Department of Neurology, Hadassah University Medical Center, PO Box 1200, Jerusalem 91120, Israel, Israel Steiner Send Correspondence to journal: Re: Smoking is a risk factor for multiple sclerosis i_biran{at}hotmail.com Iftah Biran, et al.	We read with interest the article by Riise et al.[1] The authors suggest that the risk of multiple sclerosis (MS) is higher among smokers than among never-smokers. This observation has important implications as suggested by both the accompanying editorial [2] and the Patient Page. [3] We would like, therefore, to raise several concerns: 1.) The diagnosis of MS in the population studied is based on self- report. However, the diagnosis of MS is not always clear, especially when smoking is associated with increased risk for associated vascular abnormalities,[4] yet the validity of the diagnosis in the present study was not tested. In addition, if patients with possible or probable MS do not receive the MS label from their physicians, it could lead to a severe bias in the study population. 2.) An important support for the validity of the smoking data is the clear relationship with other smoking-related disorders such as heart disease. Did the authors observe this relationship with carcinoma of the bladder which is highly linked with smoking? [5] 3.) The finding of increased prevalence of MS among smokers is interpreted by Riise et al. only to imply that smoking has a role in disease pathogenesis. However, other explanations should also be considered. These may include: smoking delineates a certain socio-economic group susceptible by means of life style to an environmental factor which will have a role in MS pathogenesis; certain personalities predispose patients to habit-forming behavior and exposure to environmental factors causing MS; an unidentified factor might trigger MS and smoking or nicotine craving behavior. We propose that currently, smoking might only serve as a marker for people with an increased risk to develop MS. References 1. Riise TMW, Nortvedt MN, Ascherio A. Smoking is a risk factor for multiple sclerosis. Neurology 2003;61:1122-1124. 2. Franklin GM, Nelson L.Environmental risk factors in multiple sclerosis: Causes, triggers, and patient autonomy. Neurology 2003;61:1032-1034. 3) Brey RL. Cigarette smoking and multiple sclerosis (MS): Yet another reason to quit. Neurology 2003;61:E11-12. 4). Steiner I, Wirguin I. Multiple sclerosis - in need of critical reappraisal. Medical Hypothesis. 2000;51:99-106. 5) Kantor AF, Hartge P, Hoover RN, Fraumeni JF Jr (1985). Familial and environmental interactions in bladder cancer risk. Int J Cancer 1985;35:703-706.
Reply to Biran et al 19 February 2004
Trond Riise, Dept. of Public Health, University of Bergen Kalfarveien 31, N-5018 Bergen, Norway, Monica W. Nortvedt, and Alberto Ascherio Send Correspondence to journal: Re: Reply to Biran et al trond.riise{at}isf.uib.no Trond Riise, et al.	We thank Biran et al for their interest in our study. Our responses follow: 1.) Biran are concerned about the validity of the diagnosis of the study subject. This is rather thoroughly discussed in our paper [1], and we are confident about the validity of the diagnosis. There may be a few cases of misclassification, but it is unlikely that this might lead to a severe bias. 2.) As this was a population-based survey, we do not have any information on carcinoma of the bladder, but the validity of the smoking data is supported by the relationship of other diseases known to be related to smoking. 3.) Regarding possible interpretations of the findings, Biran suggests three non-causal models. One is that social-economic class might be a confounding factor. This is unlikely, because the risk estimate was unchanged when adjusted for educational level, which can be considered a proxy for socio-economic class. The two other suggested relationships include a type of personality or another unidentified factor that may predispose to both MS and smoking. These cannot be excluded but have no support in the scientific literature.