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Smoking May Transform Relapsing-Remitting MS Into Secondary Progressive MS

  • Authors: News Author: Laurie Barclay, MD
    CME Author: Désirée Lie, MD, MSEd
  • CME Released: 4/27/2005
  • Valid for credit through: 4/27/2006
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Target Audience and Goal Statement

This article is intended for primary care physicians, neurologists, and other specialists who care for patients at risk of or with MS.

The goal of this activity is to provide the latest medical news to physicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • Describe the association between smoking and MS.
  • Examine the risk of secondary progression of MS associated with smoking.


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  • Laurie Barclay, MD

    Laurie Barclay is a freelance reviewer and writer for Medscape.


    Disclosure: Laurie Barclay, MD, has disclosed no relevant financial relationships.


  • Gary Vogin, MD

    Senior Medical Editor, Medscape


    Disclosure: Gary Vogin, MD, has disclosed no relevant financial relationships.

CME Author(s)

  • Desiree Lie, MD, MSEd

    Clinical Professor of Family Medicine; Director, Division of Faculty Development, University of California, Irvine School of Medicine, Irvine, California


    Charles Vega, MD, FAAFP, has disclosed that he has received grants for educational activities from Pfizer.

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Smoking May Transform Relapsing-Remitting MS Into Secondary Progressive MS

Authors: News Author: Laurie Barclay, MD CME Author: Désirée Lie, MD, MSEdFaculty and Disclosures

CME Released: 4/27/2005

Valid for credit through: 4/27/2006


April 27, 2005 — Smoking increases the risk of progression of multiple sclerosis (MS), according to the results of a study published in the March 9 Advanced Access issue of Brain.

"Compared with non-smokers, smokers had a 40-80% increased risk of multiple sclerosis in the four previously conducted prospective studies (all restricted to women)," write Miguel A. Hernán, MD, from the Harvard School of Public Health, in Boston, Massachusetts, and colleagues. "On the other hand, there are no epidemiological studies on the association between cigarette smoking and the clinical course of multiple sclerosis. Since no modifiable risk factors for multiple sclerosis progression have been identified so far, determining whether cigarette smoking affects the course of multiple sclerosis appears to be a priority."

The investigators identified patients with a first diagnosis of MS recorded in the British General Practice Research Database (GPRD) between January 1993 and December 2000. They confirmed the diagnosis and date of first symptoms by medical record review and obtained smoking status from the computer database.

To evaluate the association between smoking and MS risk, they conducted a case-control study nested in the GPRD, randomly selecting up to 10 control subjects per case. Matching was on the basis of age, sex, practice, date of joining the practice, and availability of smoking data. A cohort study of MS cases with a relapsing-remitting onset helped determine the association between smoking and progression of MS.

In the nested case-control study, which included 201 cases of MS and 1,913 controls subjects, the odds ratio (OR) of MS was 1.3 (95% confidence interval [CI], 1.0 - 1.7) for "ever smokers" compared with "never smokers." In the cohort study, with 179 cases and mean duration of follow-up of 5.3 years, the hazard ratio of secondary progression was 3.6 (95% CI, 1.3 - 9.9) for ever smokers compared with never smokers.

"These results support the hypothesis that cigarette smoking is associated with an increased risk of multiple sclerosis, and suggest that smoking may be a risk factor for transforming a relapsing-remitting clinical course into a secondary progressive course," the authors write. "We also confirmed previous findings indicating that smokers have a moderately increased risk of developing multiple sclerosis compared with non-smokers."

Study limitations may include possible confounding by other lifestyle factors or differential adherence to treatment by smoking status.

"The growing body of epidemiological evidence on the association between smoking and multiple sclerosis warrants further investigation," the authors conclude. "This line of research may provide some clues into the pathogenesis of multiple sclerosis and perhaps new insights into the prevention of the disease and its progressive forms."

The National Multiple Sclerosis Society funded this research.

Brain. Posted online March 9, 2005.