Smoking may be considered an established risk factor for sporadic ALS

Area of Science:

• Neurology
• Epidemiology

Background:

• A 2003 review identified smoking as a probable risk factor for sporadic amyotrophic lateral sclerosis (ALS).
• The review was based on limited class II evidence.

Purpose of the Study:

• To update the evidence-based review of exogenous risk factors for sporadic ALS.
• To determine if the 2003 conclusion regarding smoking as a risk factor needed modification based on newer studies.

Main Methods:

• A systematic literature search of Medline was performed for studies published between 2003 and April 2009.
• Search terms included "smoking" and variations of "amyotrophic lateral sclerosis" (ALS, MND).
• Primary articles were assessed for evidence class (II-V) to evaluate study quality.

Main Results:

• Seven articles met the inclusion criteria from 28 identified titles.
• One class II study and one class III study demonstrated an increased risk of ALS associated with smoking.
• The class II study indicated a dose-response effect and a decrease in risk with time since smoking cessation.

Conclusions:

• Smoking is confirmed as an established risk factor for sporadic amyotrophic lateral sclerosis (ALS) with a Level A rating.
• The updated evidence, including 3 class II and 1 class III studies, supports a consistent link between smoking and ALS.
• Analysis of high-quality epidemiologic data reinforces the conclusion that smoking contributes to ALS development.