Smoking Linked to Earlier Onset of MG
Also, smoking affects MG onset more in women, study finds
The onset of myasthenia gravis (MG) occurs at a significantly younger age in people who smoke, a study has found.
Women who smoked at MG onset, or within 10 years before its onset, were significantly younger at disease onset than men. Yet, no sex differences were seen among those who did not smoke.
Researchers speculated that the detrimental effect of smoking on the immune system and nerve-muscle communication might cause MG to emerge earlier.
The study, “Smoking and younger age at onset in anti-acetylcholine receptor antibody-positive myasthenia gravis,” was published in the journal Immunological Medicine.
MG is an autoimmune disorder that disrupts the regular communication between nerve cells and muscles, causing muscle weakness and fatigue.
While smoking is an established risk factor for the development and/or progression of several autoimmune diseases, its impact on MG still needs to be confirmed.
Researchers in Japan conducted a study to investigate a possible link between smoking and the age of MG onset. All eligible patients tested positive for antibodies against the acetylcholine receptor (AChR), the most common MG-causing antibody.
Among the participants, 62 were classified as never-smokers, 42 as ex-smokers, and 34 as concurrent smokers. Concurrent smokers, which made up 24.6% of the participants (15.7% women and 33.8% men), were significantly younger than patients in the other groups. The never-smoker group had significantly more female patients.
Thymomas, rare tumors in the thymus gland that are sometimes associated with MG, occurred in 24 never-smokers (38.7%), 12 ex-smokers (28.6%), and 14 current smokers (41.2%), with no significant proportional differences between the groups. In the ex-smokers group, the median time between smoking cessation and MG onset was 19 years (ranging from one to 44 years).
Analyzing the groups
Analysis revealed that MG onset occurred at a significantly younger age in those currently smoking compared with the other two groups.
Because smoking within 5–10 years before the onset of other autoimmune diseases has been shown to affect the risk of disease onset, ex-smokers who stopped smoking within 10 years of onset were combined with concurrent smokers, while those who quit smoking more than 10 years before were analyzed together with never-smokers.
Altogether, patients who smoked at MG onset, or within 10 years of its onset, were significantly younger when the disease began compared with those who did not smoke or smoked more than 10 years before. Sex and thymoma were not related to age of MG onset.
Among women, concurrent smokers were significantly younger at onset than never-smokers, whereas in men, the age at disease onset was significantly younger in concurrent smokers versus ex-smokers.
Women who smoked at MG onset, or within 10 years of its onset, were significantly younger at disease development than men, while no sex differences were seen in those who did not smoke within 10 years of disease onset.
“These observations suggested that the magnitude of the smoking effect on age at onset differs between the sexes,” the researchers wrote.
In MG patients with thymoma, the age at onset of concurrent smokers was significantly younger compared with never smokers. In non-thymoma patients, the age at disease onset was significantly younger in concurrent smokers versus ex-smokers.
Although the team found no significant differences between those with or without thymoma regarding smoking cessation time and MG onset age, patients with thymoma who smoked within 10 years of onset showed a tendency to be younger at disease onset than those without thymoma.
Statistical analysis confirmed an association between concurrent smoking and younger age at MG onset. However, no significant interactions were noted between smoking and female sex, or the presence of a thymoma. Similar results were found when concurrent smokers were combined with those who stopped smoking within 10 years of disease onset.
Finally, the researchers found that concurrent smoking was not linked to generalized symptoms affecting multiple muscle groups at MG onset.
“Smoking is an independent risk factor for the earlier development of anti-AChR antibody-positive MG,” the researchers wrote. “Our result further supports the putative link between smoking and the risk of MG.”
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