Clinical Context

It may or may not be true that the eyes are the windows to the soul, but the authors of the current study describe how the retina offers a strong approximation for volume changes in the brain and can be helpful in determining the course of disease in patients diagnosed with multiple sclerosis (MS). They explain that large studies to examine brain atrophy are limited by the resources and time required to perform magnetic resonance imaging. However, the retina is part of the central nervous system as well, and optical coherence tomography is relatively easy to perform and interpret. Specifically, the thickness of the macular ganglion cell and inner plexiform layer (mGCIPL) correlates with brain volume in the general population, as well as among patients with MS. Reduced mGCIPL is noted early in the disease course of MS and is also related to disability related to MS.

There is conflicting evidence regarding the effects of cigarette smoking and alcohol consumption on the incidence and severity of MS. The current study uses clinical history and optical coherence tomography findings of mGCIPL to further investigate the relationship between substance use and MS.

Study Synopsis and Perspective

High alcohol consumption may contribute to more severe neurodegeneration in patients with MS, and smoking may make a diagnosis of MS more likely, new research suggests.

"Our results add to the understanding of how health-associated behaviors, such as alcohol consumption and smoking, interact with neurodegeneration in MS," lead author Iris Kleerekooper, MD, clinical research fellow, Queen Square Multiple Sclerosis Center, Institute of Neurology, University College London, United Kingdom, told Medscape Medical News.

Of note, patients with MS who drank alcohol daily or almost daily had thinner retinal thicknesses, which is indicative of more brain atrophy, compared with those who drank less.

"This indicates that health advice that holds for the general population--don't smoke and consume alcohol in no more than moderate quantities--may hold extra relevance for people with MS," Dr Kleerekooper said.

The study results were published online March 3 in JAMA Network Open.

Using the UK Biobank study, the researchers investigated associations of alcohol consumption and smoking with MS diagnosis and retinal thickness in 71,981 individuals aged 40 to 69 years. Of these participants, 179 had MS.

Among the key findings was that smoking was associated with a 3-fold increased risk of receiving an MS diagnosis (odds ratio [OR], 3.05; 95% CI, 1.95-4.64).

In addition, daily or almost daily alcohol intake was associated with a thinner mGCIPL in patients with MS (adjusted β = −3.09; 95% confidence interval, −5.70 to −0.48 μm; P=.02).

Participants who said that they drank daily or almost daily had almost 5% thinner mGCIPLs, which was a substantial difference in retinal thickness, the investigators note.

Paradoxically, moderate alcohol intake, defined as consuming alcohol once per month up to 4 times per week, was associated with lower odds of an MS diagnosis.

The investigators note that a protective effect of moderate alcohol consumption on MS risk has previously been reported, although an increased risk has also been reported.

"Owing to the cross-sectional nature of the present study, the 'sick quitters' effect'--that is, the tendency to quit or profoundly limit alcohol intake when ill could have influenced our findings," they write.

Commenting for Medscape Medical News, Eoin Flanagan, MBBCh, neurologist, Mayo Clinic, Rochester, Minnesota, said that the study "highlights the detrimental effect" of cigarette smoking and consuming high amounts of alcohol.

It also "confirms the findings from many previous studies showing that smoking increases the risk of developing MS, and we also know that cigarette smoking makes MS worse," said Dr Flanagan, who was not involved with the current research.

"This gives us another reason to avoid cigarette smoking, particularly in those who already have MS," he added.

The study also indicates that "high quantities of alcohol are toxic to the retina, and that may be particularly detrimental in patients with MS, in which optic nerve and retinal damage is common from the disease itself," he noted.

"I think the take-home message for providers is that patients with MS should avoid high quantities of alcohol and cigarette smoking. Thus, public health measures that target reducing cigarette smoking could be particularly effective in helping prevent MS," Dr Flanagan concluded.

The study was funded by the postdoctoral research fellowship exchange program from the European Committee for Treatment and Research in Multiple Sclerosis and by the University College London Hospital Biomedical Research Centre. Dr Kleerekooper and Dr Flanagan have reported no relevant financial relationships.

JAMA Netw Open. Published online March 3, 2022.^[1]

Clinical Implications

• Thickness of the mGCIPL correlates with brain volume in the general population, as well as among patients with MS.
• In the current study, cigarette smoking was associated with a higher prevalence of MS but had no effect on mGCIPL thickness, whereas alcohol consumption did not affect the prevalence of MS but was associated with reduced mGCIPL thickness.
• Implications for the healthcare team: The healthcare team should consider the risks for MS in counseling patients about cigarette smoking and excessive alcohol use.

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