Patients with multiple sclerosis who continued to smoke after diagnosis had faster disease progression in a population-based, case-control study.

Each additional year of smoking after diagnosis accelerated the time to conversion to secondary progressive multiple sclerosis (SPMS) by 4.7%, and those who smoked continuously each year after diagnosis converted to SPMS an estimated 8 years earlier than did those who quit smoking at diagnosis, according to Ryan Ramanujam, Ph.D., and his colleagues.

They analyzed data from a survey of 2,538 MS patients living in Sweden, including 728 who smoked at diagnosis, 1,012 who never had smoked, and 618 who had smoked prior to having been diagnosed. The group of smokers included 118 who stopped smoking during the year after diagnosis, 332 who continued smoking, and 278 who smoked intermittently, meaning they continued smoking for at least 1 year after being diagnosed with MS and were not smoking for at least 1 year after diagnosis.

“This study demonstrates that smoking after MS diagnosis has a negative impact on the progression of the disease, whereas reduced smoking may improve patient quality of life, with more years before the development of SP disease,” the investigators wrote.

“We suggest that these results should be regarded as sufficient to recommend smoking cessation to patients,” they added.

Read the full study in JAMA Neurology (doi: 10.1001/jamaneurol.2015.1788).