Smoking is a well-established risk factor for the development of MS, but the effects of smoking on disease course after diagnosis of MS have been less clear.
A new study from researchers at the Karolinska Institutet in Stockholm, Sweden, has now shown that quitting smoking after diagnosis of MS is associated with a delay in the time taken to reach the secondary progressive phase of the disease.
The study, by Dr Ramanujam and Professor Hillert and their colleagues was published this week in the journal JAMA Neurology.
The researchers examined the data from 728 people who identified as smokers at the time of diagnosis who were registered in the Swedish Genes and Environment in Multiple Sclerosis Study, which consists of patients from the Swedish National MS Registry.
These people were then divided into two groups based on their smoking behaviour after diagnosis (continuers and quitters) and the researchers looked at the average time to diagnosis of secondary progressive disease. Continuers were defined as those who smoked at least one cigarette per day over the study time period.
They found that on average the quitters reached the secondary progressive phase of the disease 8 years later than those who continued smoking after diagnosis. This equates to a 4.7% acceleration in the time to onset of secondary progression in people who continue to smoke after an MS diagnosis.
Smoking has clearly been identified as one of the modifiable risk factors for the development of MS. The Australian Ausimmune study, in particular, provided compelling evidence that people who had experienced their first episode of demyelination, were more likely to have been smokers than healthy control individuals.
Other studies, including a study by Australian researchers in the Southern Tasmanian Longitudinal Study, have also shown that ever smoking is associated with more progressive disease and worse disability outcomes, compared to never smoking.
However, this new study is the first to provide strong evidence that quitting smoking after a diagnosis of MS can delay the onset of progressive disease in MS. The authors suggest that their study provides the evidence needed to confidently advise people with MS that quitting smoking can improve their prognosis.