Cigarette smoking and the progression of multiple sclerosis

Intracerebral Hemorrhage in Multiple Sclerosis: A Retrospective Cohort Study

BACKGROUND

To identify the vascular risk factors associated with the occurrence of intracerebral hemorrhage (ICH) in Multiple Sclerosis (MS) patients.

METHODS

This is an observational, retrospective cohort study using the nationwide electronic medical records (EMR) database. Patients with the diagnosis of MS were extracted from inpatient and outpatient EMR using the international classification of diseases, ninth/tenth revisions, clinical modification codes. We excluded patients younger than 18 years, and those where gender was not specified. Patients were further stratified based on their demographics, risk factors, medications, and comorbidities. Tobacco, diabetes, hypertension, and alcohol were the predicting variables; antiplatelet medication, and anticoagulant agents were the primary exposures for the development of ICH. A validated diagnosis code algorithm defined the diagnosis of ICH. Multivariable logistic regression models were utilized to assess the risk of ICH in MS patients.

RESULTS

Of the total 57,099 MS patients (women: 75%, n = 41,517), 107 (.19%) sustained an ICH. Age (OR = 2.74, CI = 1.13-6.62), use of anticoagulants (OR = 2.15, 95% CI = 1.30-3.56, P = .0028), and history of tobacco exposure (OR = 2.44, CI = 1.37-4.36, P = .0025) were associated with increased risk of ICH. Use of antiplatelet and disease-modifying drugs (DMDs) showed a protective trend against ICH.

CONCLUSIONS

Tobacco exposure and anticoagulant use were strongly associated with increased risk of ICH in patients with MS. There might be a protective effect that antiplatelet and DMDs have in the pathophysiology of this disease. Further prospective investigations are warranted to establish these associations.

Effects of cigarette smoke on immunity, neuroinflammation and multiple sclerosis

Cigarette smoking is the most prominent significant cause of death and morbidity. It is recognised as a risk factor for a number of immune mediated, inflammatory diseases including multiple sclerosis (MS). Here, we review the complex immunological effects of smoking on the immune system, which include enhancement of inflammatory responses with a parallel reduction of some immune defences, resulting in an increased susceptibility to infection and a persistent proinflammatory environment. We discuss the effect of smoking on the susceptibility, clinical course, disability, and mortality in MS, the likely benefits of smoking cessation, and the specific immunological effects of smoking in MS. In conclusion, smoking is an important environmental risk factor for MS occurrence and outcome, and it acts in significant part through immunological mechanisms.

Signaling pathways and therapeutic perspectives related to environmental factors associated with multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated demyelinating disorder of unknown etiology. Both genetic-susceptibility and environment exposures, including vitamin D deficiency, Epstein-Barr viral and Herpesvirus (HHV-6) infections are strongly implicated in the activation of T cells and MS-pathogenesis. Despite precise knowledge of how these factors could be operating alone or in combination to facilitate and aggravate the disease progression, it is clear that prolonged induction of inflammatory molecules and recruitment of other immune cells by the activated T cells results in demyelination and axonal damage. It is imperative to understand the risk factors associated with MS progression and how these factors contribute to disease pathology. Understanding of the underlying mechanisms of what factors triggers activation of T cells to attack myelin antigen are important to strategize therapeutics and therapies against MS. Current review provides a detailed literature to understand the role of both pathogenic and non-pathogenic factors on the impact of MS.

Smoking is associated with increased disease activity during natalizumab treatment in multiple sclerosis

Background:

Smoking has been associated with increased multiple sclerosis (MS) risk, disease worsening, and progression in MS patients. Furthermore, interactions between smoking and human leukocyte antigen (HLA) genes have been shown for MS risk. Recently, we found that smoking was associated with an increased relapse rate in interferon-beta-treated relapsing-remitting multiple sclerosis (RRMS) patients.

Objectives:

We examined the association between smoking and relapses in natalizumab-treated RRMS patients. Second, we investigated if an interaction between smoking and HLA-DRB1*15:01 or HLA-A*02:01 affected the number of relapses during treatment.

Methods:

In this observational cohort study, 355 natalizumab-treated RRMS patients were assessed. Prespecified criteria excluded 62 patients. Clinical data from the starting of treatment to the two-year follow-up visit were collected. Smoking status was obtained by a questionnaire survey. TaqMan allelic discrimination was used for genotyping of tag single-nucleotide polymorphisms (SNPs) for HLA-DRB1*15:01 and HLA-A*02:01. Negative binomial regression analysis was used to analyze the association between relapse rate and smoking intensity and HLA.

Results:

One pack of cigarettes (20 cigarettes) per day during natalizumab treatment increased the relapse rate during treatment with 38% (incidence rate ratio (IRR) = 1.38, 95% confidence interval (CI): 1.08–1.77, p = 0.01). No association or interaction was found between smoking and HLA-DRB1*15:01 or HLA-A*02:01, respectively.

Conclusion:

Smoking intensity was significantly associated with the number of relapses during natalizumab treatment.

Progressive Forms of Multiple Sclerosis: Distinct Entity or Age-Dependent Phenomena

In multiple sclerosis (MS), disease course is defined by a subclinical or clinical relapsing remitting phase, a progressive phase, and the overlapping phase in-between. Each phase can have intermittently active or inactive periods. Subclinical activity in radiologically isolated syndrome evolving to primary-progressive MS is mostly indistinguishable from relapsing-remitting MS evolving to secondary-progressive MS. The onset of progressive-phase MS is age-dependent but time and pre-progressive phase agnostic. Pathologic hallmarks of progressive MS onset also appear to be age-dependent but pre-progressive phase agnostic. Onset of progressive MS is characterized by a peak in smoldering plaques.

α-Linolenic acid is associated with MRI activity in a prospective cohort of multiple sclerosis patients

BACKGROUND

The plant-based ω-3 fatty acid α-linolenic acid (ALA) has been associated with lower MS risk. It is currently unknown whether ALA affects disease activity.

OBJECTIVE

To investigate the association between ALA levels and disease activity.

METHODS

We conducted a cohort study including 87 multiple sclerosis (MS)-patients who originally participated in a randomized trial of ω-3 fatty acids (the OFAMS study). We measured serum levels of ALA during follow-up and used random intercept logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CIs) for the association between ALA levels, new magnetic resonance imaging (MRI) lesions, Expanded Disability Status Scale (EDSS) progression and new relapses adjusting for age at inclusion, sex, and use of interferon beta-1a.

RESULTS

In continuous (per 1-SD increase) multivariable-adjusted analyses, higher ALA levels were significantly associated with lower odds of new T2-lesions (OR: 0.59, 95% CI: 0.37-0.95) during follow-up. The effect estimates were similar for new T1Gd + lesions (OR: 0.73, 95% CI: 0.48-1.11), EDSS-progression (OR: 0.62, 95% CI: 0.34-1.16) and new relapses (OR: 0.49, 95% CI: 0.22-1.10), but these estimates did not reach statistical significance. Further adjustment for vitamin D and tobacco use did not materially change the results.

CONCLUSION

We found that higher levels of ALA were associated with lower disease activity in MS-patients.

Association of Pre-Disease Body Mass Index With Multiple Sclerosis Prognosis

Both high body mass index (BMI) and smoking tobacco are known risk factors for developing multiple sclerosis (MS). However, it is unclear whether BMI, like smoking, is a risk factor for the secondary progressive (SP) course. We, therefore, sought to determine if high/low BMI at age 20 is associated to risk of SP development, in the context of smoking status. Using data from MS patients with BMI and smoking information available, we examined relapsing onset patients with MS onset after 20 years of age. Cox regressions were conducted on smokers and non-smokers, with BMI as the main exposure. In total, 5,598 relapsing onset MS patients were included. The models demonstrated that BMI > 30 was associated to increased risk of SPMS in smokers (hazard ratio 1.50, p = 0.036). This association of obesity at age 20 with increased risk of SP was not observed in non-smokers (hazard rate 0.97, p = 0.900). Since the risk is confined to smokers, the interaction observed may give insight to disease driving mechanisms.

Smoking at time of CIS increases the risk of clinically definite multiple sclerosis

BACKGROUND

Cigarette smoking is a modifiable risk factor that influences the disease course of patients with multiple sclerosis (MS). However, in patients with a clinically isolated syndrome (CIS), there are conflicting results about the association between smoking and the risk of a subsequent MS diagnosis. The aim of this study was to determine the risk of clinically definite MS (CDMS) in smoking and non-smoking patients at time of a first demyelinating event.

METHODS

Two hundred and fifty patients, aged 18-50 years, were included in our prospective CIS cohort. At time of the first neurological symptoms, patients completed a questionnaire about smoking habits. Cox regression analyses were performed to calculate univariate and multivariate hazard ratios for CDMS diagnosis in smoking and non-smoking CIS patients.

RESULTS

One hundred and fourteen (46%) CIS patients were diagnosed with CDMS during a mean follow-up of 58 months. In total, 79 (32%) patients smoked at time of CIS. Sixty-seven % of the smoking CIS patients were diagnosed with CDMS during follow-up compared to 36% of the non-smoking CIS patients (p < 0.001). Smoking at time of CIS was an independent predictor for CDMS diagnosis (HR 2.3; p = 0.002). Non-smoking CIS patients who had a history of smoking did not have a higher risk for CDMS than those who had never smoked.

CONCLUSIONS

Smoking at time of CIS was an independent risk factor for a future CDMS diagnosis. This is an additional argument to quit smoking at time of the first attack of suspected MS.

Smoking affects the interferon beta treatment response in multiple sclerosis

Objective

To investigate whether smoking in patients with relapsing-remitting multiple sclerosis (RRMS) treated with interferon beta (IFN-β) is associated with the relapse rate and whether there is an interaction between smoking and human leukocyte antigen (HLA)–DRB1*15:01, HLA-A*02:01, and the N-acetyltransferase-1 (NAT1) variant rs7388368A.

Methods

DNA from 834 IFN-β–treated patients with RRMS from the Danish Multiple Sclerosis Biobank was extracted for genotyping. Information about relapses from 2 years before the start of treatment to either the end of treatment or the last follow-up visit was obtained from the Danish Multiple Sclerosis Treatment Register. Smoking information came from a comprehensive questionnaire.

Results

We found that the relapse rate in patients with RRMS during IFN-β treatment was higher in smokers compared to nonsmokers, with an incidence rate ratio (IRR) of 1.20 (95% confidence interval [CI] 1.021–1.416, p = 0.027) and with an IRR increase of 27% per pack of cigarettes per day (IRR 1.27, 95% CI 1.056–1.537, p = 0.012). We found no association or interaction with HLA and the NAT1 variant.

Conclusion

In this observational cohort study, we found that smoking is associated with increased relapse activity in patients with RRMS treated with IFN-β, but we found no association or interaction with HLA or the NAT1 variant.

Exposure to particulate matter air pollution and risk of multiple sclerosis in two large cohorts of US nurses

BACKGROUND

Air pollution is thought to raise the risk of neurological disease by promoting neuroinflammation, oxidative stress, glial activation and cerebrovascular damage. Multiple Sclerosis is a common auto-immune disorder, primarily affecting young women. We conducted, to a large prospective study of particulate matter (PM) exposure and multiple sclerosis (MS) risk in two prospective cohorts of women: the Nurses Health Study (NHS) and the Nurses Health Study II (NHS II).

METHODS

Cumulative average exposure to different size fractions of PM up to the onset of MS was estimated using spatio-temporal models. We used multivariable Cox proportional hazards models to estimate the hazard ratios (HR) and 95% confidence intervals (CI) of MS associated with each size fraction of PM independently. Participants were followed from 1998 through 2004 in NHS and from 1988 through 2007 for NHS II. We conducted additional sensitivity analyses stratified by smoking, region of the US, and age, as well as analyses restricted to women who did not move during the study. Analyses were adjusted for age, ancestry, smoking, body mass index at age 18, region, tract level population density, latitude at age 15, and UV index.

RESULTS

We did not observe significant associations between air pollution and MS risk in our cohorts. Among women in the NHS II, the HRs comparing the top vs. bottom quintiles of PM was 1.11 (95% Confidence Intervals (CI): 0.74, 1.66), 1.04 (95% CI: 0.73, 1.50) and 1.09 (95% CI: 0.73, 1.62) for PM₁₀ (≤10μm in diameter), PM_2.5 (≤2.5μm in diameter), and PM_2.5-10 (2.5 to 10μm in diameter) respectively, and tests for linear trends were not statistically significant. No association between exposure to PM and risk of MS was observed in the NHS.

CONCLUSIONS

In this study, exposure to PM air pollution was not related to MS risk.

Wellness and the Role of Comorbidities in Multiple Sclerosis

Multiple sclerosis (MS) is a demyelinating and neurodegenerative disorder of the central nervous system, for which disease modifying therapies (DMTs) are the mainstay treatment approach to reduce inflammatory disease activity and slow worsening disability. In addition to conventional pharmacologic therapy, there is growing interest in the use of lifestyle strategies to support wellness and mitigate disease-related complications in MS. This interest stems from a growing appreciation of the role of certain comorbidities and lifestyle factors on disease activity, disability, mortality, and overall quality of life. While the current literature is not conclusive, there is evidence to suggest a potential role for vitamin D supplementation, tobacco smoking cessation, routine exercise, a plant-based, anti-inflammatory diet, and maintenance of emotional well-being as adjunct therapies to DMTs. In addition to DMTs, lifestyle strategies should be emphasized as part of a management plan focused on overall health and well-being.

Oral Administration of the Probiotic Strain Escherichia coli Nissle 1917 Reduces Susceptibility to Neuroinflammation and Repairs Experimental Autoimmune Encephalomyelitis-Induced Intestinal Barrier Dysfunction

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with an increasing incidence in developed countries. Recent reports suggest that modulation of the gut microbiota might be one promising therapy for MS. Here, we investigated whether the probiotic Escherichia coli strain Nissle 1917 (ECN) could modulate the outcome of experimental autoimmune encephalomyelitis (EAE), a murine model of MS. We evidenced that daily oral treatment with ECN, but not with the archetypal K12 E. coli strain MG1655, reduced the severity of EAE induced by immunization with the MOG_35-55 peptide. This beneficial effect was associated with a decreased secretion of inflammatory cytokines and an increased production of the anti-inflammatory cytokine IL-10 by autoreactive CD4 T cells, both in peripheral lymph nodes and CNS. Interestingly, ECN-treated mice exhibited increased numbers of MOG-specific CD4⁺ T cells in the periphery contrasting with severely reduced numbers in the CNS, suggesting that ECN might affect T cell migration from the periphery to the CNS through a modulation of their activation and/or differentiation. In addition, we demonstrated that EAE is associated with a profound defect in the intestinal barrier function and that treatment with ECN, but not with MG1655, repaired intestinal permeability dysfunction. Collectively, our data reveal that EAE induces a disruption of the intestinal homeostasis and that ECN protects from disease and restores the intestinal barrier function.

Smoking does not influence disability accumulation in primary progressive multiple sclerosis

BACKGROUND AND PURPOSE

The modifiable risk factor cigarette smoking has been associated with an increased risk of developing multiple sclerosis (MS) and with disease activity in relapsing-remitting MS. However, less is known about the effect of smoking on disease progression in progressive MS. Here the association between cigarette smoking and disability accumulation in primary progressive MS (PPMS) is investigated.

METHODS

Kaplan-Meier survival analyses and Cox proportional hazard modelling were used to investigate the influence of cigarette smoking on the risk of reaching Expanded Disability Status Scale (EDSS) 4 and 6 as well as the time from EDSS 4 to 6 in patients with PPMS.

RESULTS

In all, 416 patients with PPMS and available smoking history were identified. Median time to EDSS 4 was 4 years in ever-smokers and 5 years in never-smokers (P = 0.27), and it was 9 years to EDSS 6 in both ever-smokers and never-smokers (P = 0.48). Smokers were not at increased risk of faster progression to EDSS 4, 6 and from EDSS 4 to 6. Age at disease onset was the strongest risk factor for progression to EDSS 4, 6 and from EDSS 4 to 6.

CONCLUSIONS

Our investigation of a large and well-characterized population based PPMS cohort suggests that cigarette smoking does not influence disability accumulation in PPMS. Our findings support the idea that PPMS is driven by different underlying pathomechanisms than relapsing-remitting MS.

Development of an algorithm for determining smoking status and behaviour over the life course from UK electronic primary care records

Background

Patients’ smoking status is routinely collected by General Practitioners (GP) in UK primary health care. There is an abundance of Read codes pertaining to smoking, including those relating to smoking cessation therapy, prescription, and administration codes, in addition to the more regularly employed smoking status codes. Large databases of primary care data are increasingly used for epidemiological analysis; smoking status is an important covariate in many such analyses. However, the variable definition is rarely documented in the literature.

Methods

The Secure Anonymised Information Linkage (SAIL) databank is a repository for a national collection of person-based anonymised health and socio-economic administrative data in Wales, UK. An exploration of GP smoking status data from the SAIL databank was carried out to explore the range of codes available and how they could be used in the identification of different categories of smokers, ex-smokers and never smokers. An algorithm was developed which addresses inconsistencies and changes in smoking status recording across the life course and compared with recorded smoking status as recorded in the Welsh Health Survey (WHS), 2013 and 2014 at individual level. However, the WHS could not be regarded as a “gold standard” for validation.

Results

There were 6836 individuals in the linked dataset. Missing data were more common in GP records (6%) than in WHS (1.1%). Our algorithm assigns ex-smoker status to 34% of never-smokers, and detects 30% more smokers than are declared in the WHS data. When distinguishing between current smokers and non-smokers, the similarity between the WHS and GP data using the nearest date of comparison was κ = 0.78. When temporal conflicts had been accounted for, the similarity was κ = 0.64, showing the importance of addressing conflicts.

Conclusions

We present an algorithm for the identification of a patient’s smoking status using GP self-reported data. We have included sufficient details to allow others to replicate this work, thus increasing the standards of documentation within this research area and assessment of smoking status in routine data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12911-016-0400-6) contains supplementary material, which is available to authorized users.

Interactions between genetic, lifestyle and environmental risk factors for multiple sclerosis

Genetic predisposition to multiple sclerosis (MS) only explains a fraction of the disease risk; lifestyle and environmental factors are key contributors to the risk of MS. Importantly, these nongenetic factors can influence pathogenetic pathways, and some of them can be modified. Besides established MS-associated risk factors - high latitude, female sex, smoking, low vitamin D levels caused by insufficient sun exposure and/or dietary intake, and Epstein-Barr virus (EBV) infection - strong evidence now supports obesity during adolescence as a factor increasing MS risk. Organic solvents and shift work have also been reported to confer increased risk of the disease, whereas factors such as use of nicotine or alcohol, cytomegalovirus infection and a high coffee consumption are associated with a reduced risk. Certain factors - smoking, EBV infection and obesity - interact with HLA risk genes, pointing at a pathogenetic pathway involving adaptive immunity. All of the described risk factors for MS can influence adaptive and/or innate immunity, which is thought to be the main pathway modulated by MS risk alleles. Unlike genetic risk factors, many environmental and lifestyle factors can be modified, with potential for prevention, particularly for people at the greatest risk, such as relatives of individuals with MS. Here, we review recent data on environmental and lifestyle factors, with a focus on gene-environment interactions.

No association of tobacco use and disease activity in multiple sclerosis

Objective:

To study whether tobacco use is associated with MRI and clinical disease activity in patients with multiple sclerosis (MS).

Methods:

Prospective cohort study of 87 patients with relapsing-remitting MS originally included in a randomized placebo-controlled trial of omega-3 fatty acids in MS (the OFAMS Study). Serum levels of cotinine (biomarker of tobacco use) were analyzed at baseline and every 6 months for 2 years. MRI activity was assessed at baseline and monthly for 9 months and after 12 and 24 months.

Results:

Fifty-three patients (61%) had serum cotinine levels ≥85 nmol/L on ≥60% of the measurements and were considered tobacco users and 34 (39%) had cotinine levels <85 nmol/L, consistent with non–tobacco use. There was no association between tobacco use and the occurrence of new gadolinium-enhancing T1 lesions, new or enlarging T2 lesions, or their aggregate (combined unique activity). Furthermore, there was no association between cotinine levels and MRI activity for the tobacco users, and tobacco users did not have more relapses or Expanded Disability Status Scale progression.

Conclusion:

Our results indicate that tobacco use does not directly influence MRI activity or relapse rate in MS. This may implicate that the reported association between smoking and MS disease progression could be mediated through other mechanisms.

Cigarette smoking and autoimmune disease: what can we learn from epidemiology?

Cigarette smoking has been causally linked to the development of multiple autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, Graves' hyperthyroidism, and primary biliary cirrhosis, among others. We review the known biologic effects of cigarette smoke, in particular its actions on the immune system, and the epidemiologic evidence associating smoking with increased risk of each of these autoimmune diseases. Interactions between cigarette smoking and genetic and immunologic factors, such as the human leukocyte antigen (HLA)shared epitope, rheumatoid factor, anti-cyclic citrullinated peptide antibodies, and anti-double stranded DNA antibodies, may point to mechanisms in disease pathogenesis.

Elevated urinary excretion of aluminium and iron in multiple sclerosis

Multiple sclerosis (MS) is a chronic, immune-mediated, demyelinating disease of the central nervous system of as yet unknown aetiology. A consensus of opinion has suggested that the disorder is the result of an interplay between environmental factors and susceptibility genes. We have used a battery of analytical techniques to determine if the urinary excretion of i) markers of oxidative damage; ii) iron and iii) the environmental toxin aluminium and its antagonist, silicon, are altered in relapsing remitting (RRMS) and secondary progressive MS (SPMS). Urinary concentrations of oxidative biomarkers, MDA and TBARS, were not found to be useful indicators of inflammatory disease in MS. However, urinary concentrations of another potential marker for inflammation and oxidative stress, iron, were significantly increased in SPMS ( P<0.01) and insignificantly increased in RRMS ( P>0.05). Urinary concentrations of aluminium were also significantly increased in RRMS ( P<0.001) and SPMS ( P<0.05) such that the levels of aluminium excretion in the former were similar to those observed in individuals undergoing metal chelation therapy. The excretion of silicon was lower in MS and significantly so in SPMS ( P<0.05). Increased excretion of iron in urine supported a role for iron dysmetabolism in MS. Levels of urinary aluminium excretion similar to those seen in aluminium intoxication suggested that aluminium may be a hitherto unrecognized environmental factor associated with the aetiology of MS. If aluminium is involved in MS then an increased dietary intake of its natural antagonist, silicon, might be a therapeutic option.

Population attributable fractions and joint effects of key risk factors for multiple sclerosis

AIM

We examined the combined effect of having multiple key risk factors and the interactions between the key risk factors of multiple sclerosis (MS).

METHODS

We performed an incident case-control study including cases with a first clinical diagnosis of central nervous system demyelination (FCD) and population-based controls.

RESULTS

Compared to those without any risk factors, those with one, two, three, and four or five risk factors had increased odds of being an FCD case of 2.12 (95% confidence interval (CI), 1.11-4.03), 4.31 (95% CI, 2.24-8.31), 7.96 (95% CI, 3.84-16.49), and 21.24 (95% CI, 5.48-82.40), respectively. Only HLA-DR15 and history of infectious mononucleosis interacted significantly on the additive scale (Synergy index, 3.78; p = 0.03). The five key risk factors jointly accounted for 63.8% (95% CI, 43.9-91.4) of FCD onset. High anti-EBNA IgG was another important contributor.

CONCLUSIONS

A high proportion of FCD onset can be explained by the currently known risk factors, with HLA-DR15, ever smoking and low cumulative sun exposure explaining most. We identified a significant interaction between HLA-DR15 and history of IM in predicting an FCD of CNS demyelination, which together with previous observations suggests that this is a true interaction.

The risk of smoking on multiple sclerosis: a meta-analysis based on 20,626 cases from case-control and cohort studies

Background. Multiple sclerosis (MS) has become a disease that represents a tremendous burden on patients, families, and societies. The exact etiology of MS is still unclear, but it is believed that a combination of genetic and environmental factors contribute to this disease. Although some meta-analyses on the association between smoking and MS have been previously published, a number of new studies with larger population data have published since then. Consequently, these additional critical articles need to be taken into consideration.

Method. We reviewed articles by searching in PubMed and EMBASE. Both conservative and non-conservative models were used to investigate the association between smoking and the susceptibility to MS. We also explored the effect of smoking on the susceptibility to MS in strata of different genders and smoking habits. The association between passive smoking and MS was also explored.

Results.The results of this study suggest that smoking is a risk factor for MS (conservative model: odds ratio (OR) 1.55, 95% CI [1.48–1.62], p < 0.001; non-conservative model: 1.57, 95% CI [1.50–1.64], p < 0.001). Smoking appears to increase the risk of MS more in men than in women and in current smokers more than in past smokers. People who exposed to passive smoking have higher risk of MS than those unexposed.

Conclusion.This study demonstrated that exposure to smoking is an important risk factor for MS. People will benefit from smoking cessation, and policymakers should pay attention to the association between smoking and MS.

What role does tobacco smoking play in multiple sclerosis disability and mortality? A review of the evidence

There is increasing evidence of tobacco smoking as an associative factor in multiple sclerosis (MS). Numerous studies have been conducted investigating the effects of smoking before the onset of MS as well as its impact on disease course. This special report reviews the available evidence and summarizes the contribution of smoking to increased mortality in patients with MS. It also explores some putative mechanisms for the involvement of tobacco constituents in the pathology of MS and the effects of smoking on disease-modifying treatments.

Environmental Factors and Their Regulation of Immunity in Multiple Sclerosis

In multiple sclerosis (MS), environmental factors and genetic traits cooperate in the induction of the chronic activation of immune cells to produce the brain pathology. Epidemiology has focused on different environmental risk factors but certainly virus infection, smoking, vitamin D levels, and sunlight exposure are the most relevant. What is certainly less clear is the way in which these external factors are able to induce and sustain the internal pathology process of the disease. Epigenetics has been recently focused on trying to shed light on this aspect. As a matter of fact epigenetic changes are highly sensitive to environmental factors that therefore may influence the susceptibility to the disease by acting through epigenetic modifications. In this chapter we discuss the most relevant environmental factors and how they may affect the immune response in MS. Finally, we discuss the possible role of the microbiota in inducing autoimmunity in MS.

The epidemiology of multiple sclerosis: insights to a causal cascade

MS-pathogenesis involves both genetic-susceptibility and environmental determinants. Three (or more) sequential environmental-factors are implicated. The first acts near birth, the second acts during childhood/adolescence, and the third acts subsequently. Two candidate factors (vitamin D deficiency and Epstein-Barr viral infection) seem particularly well-suited to the first two environmental-events but other factors (e.g., obesity and smoking behavior) seem also to be involved in the causal scheme. MS-pathogenesis can be modeled by incorporating both the environmental and genetic-factors into a causal scheme, which can then help to explain some of the changes in MS-epidemiology (e.g., increasing disease-prevalence, changing sex-ratio, and regional-variations in monozygotic-twin-concordance-rates), which have been taking place recently. This model suggests that genetic-susceptibility is overwhelmingly the most important determinant of MS and that, at least, 92.5% of individuals (and likely much more) are, essentially, incapable of developing MS, regardless of their specific environmental-exposures. Nevertheless, the genetics is complex and the contribution of any specific gene to MS-susceptibility seems to be quite modest. Thus, even for the DRB1*1501 allele (the strongest known MS-susceptibility marker), most carriers are not in the genetically-susceptible group. Moreover, 45-50% of individuals with MS lack this allele entirely and some of the haplotypes that carry this allele don't also confer any disease-risk. Finally, because the prevalence of genetic-susceptibility seems to be so similar throughout North America and Europe, and despite the crucial importance of a person's genetic make-up to disease pathogenesis, it is the environmental-factors, which largely responsible for the observed regional variations in disease-characteristics. Thus, despite MS being more common in women, men are more likely to be genetically-susceptible. This apparent paradox seems to relate to the fact that women are much more responsive than men to the recent changes in environmental-exposure (whatever these have been). These gender-differences may help to explain changes in the sex-ratio and the increasing disease-prevalence, which have both been observed recently. The potential importance of these conclusions regarding the role of environment in MS-pathogenesis is that they open the door to the possibility of pursuing strategies for primary primary disease prevention in the future.

Melatonin Contributes to the Seasonality of Multiple Sclerosis Relapses

Seasonal changes in disease activity have been observed in multiple sclerosis, an autoimmune disorder that affects the CNS. These epidemiological observations suggest that environmental factors influence the disease course. Here, we report that melatonin levels, whose production is modulated by seasonal variations in night length, negatively correlate with multiple sclerosis activity in humans. Treatment with melatonin ameliorates disease in an experimental model of multiple sclerosis and directly interferes with the differentiation of human and mouse T cells. Melatonin induces the expression of the repressor transcription factor Nfil3, blocking the differentiation of pathogenic Th17 cells and boosts the generation of protective Tr1 cells via Erk1/2 and the transactivation of the IL-10 promoter by ROR-α. These results suggest that melatonin is another example of how environmental-driven cues can impact T cell differentiation and have implications for autoimmune disorders such as multiple sclerosis.

Genes and Environment in Multiple Sclerosis project: A platform to investigate multiple sclerosis risk

The Genes and Environment in Multiple Sclerosis project establishes a platform to investigate the events leading to multiple sclerosis (MS) in at-risk individuals. It has recruited 2,632 first-degree relatives from across the USA. Using an integrated genetic and environmental risk score, we identified subjects with twice the MS risk when compared to the average family member, and we report an initial incidence rate in these subjects that is 30 times greater than that of sporadic MS. We discuss the feasibility of large-scale studies of asymptomatic at-risk subjects that leverage modern tools of subject recruitment to execute collaborative projects.

Genetic, Epigenetic, and Environmental Factors Influencing Neurovisceral Integration of Cardiovascular Modulation: Focus on Multiple Sclerosis

Thought to be an autoimmune inflammatory CNS disease, multiple sclerosis (MS) involves multiple pathologies with heterogeneous clinical presentations. An impaired neurovisceral integration of cardiovascular modulation, indicated by sympathetic and parasympathetic autonomic nervous system (ANS) dysfunction, is among common MS clinical presentations. ANS dysfunction could not only enhance MS inflammatory and neurodegenerative processes, but can also lead to clinical symptoms such as depression, fatigue, sleep disorder, migraine, osteoporosis, and cerebral hemodynamic impairments. Therefore, factors influencing ANS functional activities, in one way or another, will have a significant impact on MS disease course. This review describes the genetic and epigenetic factors, and their interactions with a number of environmental factors contributing to the neurovisceral integration of cardiovascular modulation, with a focus on MS. Future studies should investigate the improvement in cardiovascular ANS function, as a strategy for preventing and minimizing MS-related morbidities, and improving patients' quality of life.

No association of multiple sclerosis activity and progression with EBV or tobacco use in BENEFIT

OBJECTIVE

To evaluate whether Epstein-Barr virus (EBV) immunoglobulin G (IgG) antibody levels or tobacco use were associated with conversion to multiple sclerosis (MS) or MS progression/activity in patients presenting with clinically isolated syndrome (CIS).

METHODS

In this prospective, longitudinal study, we measured EBV IgG antibody and cotinine (biomarker of tobacco use) levels at up to 4 time points (baseline, months 6, 12, and 24) among 468 participants with CIS enrolled in the BENEFIT (Betaferon/Betaseron in Newly Emerging Multiple Sclerosis for Initial Treatment) clinical trial. Outcomes included time to conversion to clinically definite or McDonald MS, number of relapses, Expanded Disability Status Scale (EDSS) changes, brain and T2 lesion volume changes, and number of new active lesions over 5 years. Analyses were adjusted for age, sex, treatment allocation, baseline serum 25-hydroxyvitamin D level, number of T2 lesions, body mass index, EDSS, steroid treatment, and CIS onset type.

RESULTS

We found no associations between any EBV IgG antibody or cotinine levels with conversion from CIS to MS or MS progression as measured by EDSS or activity clinically or on MRI. The relative risk of conversion from CIS to clinically definite MS was 1.14 (95% confidence interval 0.76-1.72) for the highest vs the lowest quintile of EBNA-1 IgG levels, and 0.96 (95% confidence interval 0.71-1.31) for cotinine levels >25 ng/mL vs <10.

CONCLUSIONS

Neither increased levels of EBV IgG antibodies, including against EBNA-1, nor elevated cotinine levels indicative of tobacco use, were associated with an increased risk of CIS conversion to MS, or MS activity or progression over a 5-year follow-up.

Epidemiology of multiple sclerosis: results from a large observational study in the UK

Multiple sclerosis (MS) progression to mortality may not be solely determined by the underlying autoimmune process. We conducted a study in a large cohort of MS patients with the aim of describing characteristics of MS patients and identification of predictors for all-cause mortality in this patient group. We performed a retrospective analysis of primary care data from the UK Clinical Practice Research Datalink. Incident MS cases diagnosed between 1993 and 2006 were identified and validated using electronic and original medical records. Patients were followed to identify deaths; hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional regression with age as time-scale. In total, 1713 incident MS cases were identified. Following MS diagnosis, frequent comorbidities were infections (80%), and depression (46%). Adjusted HRs (95% CIs) for all-cause mortality were: 2.0 (1.2-3.4) for current smoking; 7.6 (3.2-17.7) for alcohol abuse; 2.7 (1.6-4.5) for pneumonia and influenza; 4.1 (2.7-6.3) for urinary tract infections; 2.2 (1.2-4.2) for heart disease and 4.9 (2.9-8.0) for cancer. Our results suggest that MS survival is influenced not only by the underlying autoimmune process, but also by patient comorbidities and lifestyle factors.

Epigenetic changes in neurology: DNA methylation in multiple sclerosis

INTRODUCTION

Epigenetics is defined as the study of the mechanisms that regulate gene expression without altering the underlying DNA sequence. The best known is DNA methylation. Multiple Sclerosis (MS) is a disease with no entirely known etiology, in which it is stated that the involvement of environmental factors on people with a genetic predisposition, may be key to the development of the disease. It is at this intersection between genetic predisposition and environmental factors where DNA methylation may play a pathogenic role.

DEVELOPMENT

A literature review of the effects of environmental risk factors for the development of MS can have on the different epigenetic mechanisms as well as the implication that such changes have on the development of the disease.

CONCLUSION

Knowledge of epigenetic modifications involved in the pathogenesis of MS, opens a new avenue of research for identification of potential biomarkers, as well as finding new therapeutic targets.

Association between Smoking and Uveitis: Results from the Pacific Ocular Inflammation Study

PURPOSE

To assess whether cigarette smoking is associated with the development of uveitis in a population-based setting.

DESIGN

Retrospective, population-based, case-control study.

PARTICIPANTS

Patients aged ≥ 18 years who were seen at a Kaiser Permanente Hawaii clinic between January 1, 2006, and December 31, 2007. Analysis included 100 confirmed incident uveitis cases, 522 randomly selected controls from the general Kaiser Hawaii population, and 528 randomly selected controls from the Kaiser Hawaii ophthalmology clinic.

METHODS

International Classification of Diseases, 9th revision (ICD-9), diagnosis codes were used to identify possible uveitis cases. A uveitis fellowship-trained ophthalmologist then conducted individual chart review to confirm case status. Multivariate logistic regression models were used to evaluate the association between smoking and uveitis, adjusting for age, sex, race, and socioeconomic status.

MAIN OUTCOME MEASURES

Development of uveitis.

RESULTS

Current smokers had a 1.63 (95% confidence interval [CI], 0.88-3.00; P = 0.12) and 2.33 (95% CI, 1.22-4.45; P = 0.01) times greater odds of developing uveitis compared with those who never smoked using the general and ophthalmology control groups, respectively. The association was even stronger with noninfectious uveitis, which yielded odds ratios of 2.10 (95% CI, 1.10-3.99; P = 0.02) and 2.96 (95% CI, 1.52-5.77; P = 0.001) using the general and ophthalmology control groups, respectively.

CONCLUSIONS

Cigarette smoking is significantly associated with new-onset uveitis within a population-based setting. The association was stronger for noninfectious uveitis. Given the well-established risks of smoking with regard to other inflammatory disorders, these results reaffirm the importance of encouraging patients to avoid or cease smoking.

Risk factors associated with the onset of relapsing-remitting and primary progressive multiple sclerosis: a systematic review

Multiple sclerosis (MS) is a chronic central nervous system disease with a highly heterogeneous course. The aetiology of MS is not well understood but is likely a combination of both genetic and environmental factors. Approximately 85% of patients present with relapsing-remitting MS (RRMS), while 10–15% present with primary progressive MS (PPMS). PPMS is associated with an older onset age, a different sex ratio, and a considerably more rapid disease progression relative to RRMS. We systematically reviewed the literature to identify modifiable risk factors that may be associated with these different clinical courses. We performed a search of six databases and integrated twenty observational studies into a descriptive review. Exposure to Epstein-Barr virus (EBV) appeared to increase the risk of RRMS, but its association with PPMS was less clear. Other infections, such as human herpesvirus-6 and chlamydia pneumoniae, were not consistently associated with a specific disease course nor was cigarette smoking. Despite the vast literature examining risk factors for the development of MS, relatively few studies reported findings by disease course. This review exposes a gap in our understanding of the risk factors associated with the onset of PPMS, our current knowledge being predominated by relapsing-onset MS.

Tobacco smoking and excess mortality in multiple sclerosis: a cohort study

OBJECTIVE

As patients with multiple sclerosis (MS) have more than 2.5-fold increased mortality risk, we sought to investigate the impact of tobacco smoking on the risk of premature death and its contribution to the excess mortality in MS patients.

METHODS

We studied 1032 patients during the period 1994-2013 in a UK-based register. Cox regression model was used to investigate the impact of smoking on the risk of premature death, controlling for confounders. Smoking-specific mortality rates were compared with the UK general population.

RESULTS

Of 923 patients with clinically definite MS, 80 (46 males and 34 females) had died by December 2012. HRs for death in current smokers and ex-smokers relative to never smokers were 2.70 (95% CI 1.59 to 4.58, p<0.001) and 1.30 (95% CI 0.72 to 2.32; p = 0.37). The standardised mortality ratio, compared with the UK general population, when stratified by smoking status was 3.83 (95% CI 2.71 to 5.42) in current smokers, 1.96 (95% CI 1.27 to 3.0) in ex-smokers and 1.27 (95% CI 0.87 to 1.86) in non-smokers. Never smokers and ex-smokers with MS had similar mortality rates compared with never smokers and ex-smokers without MS in the male British doctors cohort (1.12 (95% CI 0.63 to 1.97) and 0.54 (95% CI 0.26 to 1.14), respectively), while current smokers with MS had 84% higher rate of death compared with current smokers without MS (95% CI 1.24 to 2.72).

CONCLUSIONS

Tobacco smoking can account for some of the excess mortality associated with MS and is a risk determinant for all-cause and MS-related death.

The epidemiology of multiple sclerosis: insights to disease pathogenesis

The purpose of studying the epidemiology of multiple sclerosis (MS) is twofold. First, it is important to understand clearly the natural history of the illness in order to assist patients in making decisions about their future with respect to issues such as family planning, the importance of securing lifelong healthcare, their ability to get and maintain employment, and making appropriate choices of therapy for their particular circumstances. This is not to suggest that, even with the best possible information, the ultimate prognosis for any individual can be predicted with absolute accuracy. It cannot. Nevertheless, accurate information can be very helpful both to reassure patients that many individuals with MS do remarkably well in the long term (perhaps, especially, with current and future therapies) and also to empower individuals with respect to their ability to make their own life choices. Second, and arguably the more important purpose for studying the epidemiology of MS, is to gain insights to the underlying causes of the disease. Indeed, if the principal mechanisms of disease pathogenesis were to be understood clearly, then it might be possible to entertain notions of either a cure for existing disease or the primary prevention of future disease. Much of our current understanding of disease pathogenesis, as discussed in other chapters of this volume, has been derived from basic science investigations of animal models of MS such as experimental autoimmune encephalomyelitis (EAE), and these models have provided considerable insight both to the complexity of the mammalian immune system and to the mechanisms underlying its dysfunction in inflammatory autoimmune conditions. Nevertheless, MS is a disease of humans without any known, naturally occurring, counterpart in any nonhuman species. For this reason, the clues to disease pathogenesis provided by a study of basic epidemiologic facts regarding MS (and by a systematic consideration of their implications) are essential to a comprehensive understanding of the human illness we call MS.

Gender differences in autoimmune disease

Autoimmune diseases are a range of diseases in which the immune response to self-antigens results in damage or dysfunction of tissues. Autoimmune diseases can be systemic or can affect specific organs or body systems. For most autoimmune diseases there is a clear sex difference in prevalence, whereby females are generally more frequently affected than males. In this review, we consider gender differences in systemic and organ-specific autoimmune diseases, and we summarize human data that outlines the prevalence of common autoimmune diseases specific to adult males and females in countries commonly surveyed. We discuss possible mechanisms for sex specific differences including gender differences in immune response and organ vulnerability, reproductive capacity including pregnancy, sex hormones, genetic predisposition, parental inheritance, and epigenetics. Evidence demonstrates that gender has a significant influence on the development of autoimmune disease. Thus, considerations of gender should be at the forefront of all studies that attempt to define mechanisms that underpin autoimmune disease.

Clinical features and disability progression in multiple sclerosis in Tunisia: do we really have a more aggressive disease course?

BACKGROUND

Few epidemiological data are available on multiple sclerosis (MS) patients in North Africa (NA). Studies of immigrants from NA showed a more aggressive course compared to European patients.

OBJECTIVE

The aim of this study is to describe clinical and long term course characteristics of MS in Tunisia and to compare it to European cohorts.

METHOD

A total of 437 MS patients from three hospital based cohorts in Tunisia and having prospective follow up between 2010 and 2012 were analyzed. We considered as endpoints the time to reach EDSS scores of 3, 4 and 6 in the different clinical forms of MS and the beginning of a secondary progressive (SP) phase.

RESULTS

Sex ratio was 2.34. Mean age of onset was 30.3 years. The course was relapsing-remitting (RR) in 91% of patients and primary progressive (PP) in 9%. The most frequent isolated onset symptoms were respectively motor (28%), optic neuritis (20%) and sensory (16%) dysfunction. Median time to SP onset was 19.1 years. Median times from onset of multiple sclerosis to assignment of a score of 3, 4 and 6 were 8, 10.7 and 15 years respectively. Benign form of MS represented 31.5%. Median interval from the onset of the disease to EDSS score of 3, 4 and 6 was shorter in PP-MS than in RR-MS. However, there was no difference between these two groups for the median time from the assignment of EDSS 4 to the assignment EDSS 6.

CONCLUSIONS

Our study shows that Tunisian MS patients have a quite similar clinical feature to European patients. Still, larger MS multicenter cohort studies in NA with longer follow-up duration could clearly respond to the issue.

Mortality of patients with multiple sclerosis: a cohort study in UK primary care

We aimed to estimate rates, causes and risk factors of all-cause mortality in a large population-based cohort of multiple sclerosis (MS) patients compared with patients without MS. Using data from the UK General Practice Research Database, we identified MS cases diagnosed during 2001–2006 and validated using patients’ original records where possible. We also included MS cases during 1993–2000 identified and validated in an earlier study. Cases were matched to up to ten referents without MS by age, sex, index date (date of first MS diagnosis for cases and equivalent reference date for controls), general practice and length of medical history before first MS diagnosis. Patients were followed up to identify deaths; hazard ratios (HRs) and 95 % confidence intervals (CIs) were estimated using Cox-proportional regression. MS patients (N = 1,822) had a significantly increased risk of all-cause mortality compared with referents (N = 18,211); adjusted HR 1.7 (95 % CI 1.4–2.1). Compared with referents, female MS patients had a higher but not significantly different HR for death than males; adjusted HR 1.86 (95 % CI 1.46–2.38) vs. HR 1.31 (95 % CI 0.93–1.84), respectively. The most commonly recorded cause of death in MS patients was ‘MS’ (41 %), with a higher proportion recorded among younger patients. A significantly higher proportion of referents than MS patients had cancer recorded as cause of death (40 vs. 19 %). Patients with MS have a significant 1.7-fold increased risk of all-cause mortality compared with the general population. MS is the most commonly recorded cause of death among MS patients.

Association between Smoking and Health Outcomes in Postmenopausal Women Living with Multiple Sclerosis

Background. In multiple sclerosis (MS), symptom management and improved health-related quality of life (HrQOL) may be modified by smoking. Objective. To evaluate the extent to which smoking is associated with worsened health outcomes and HrQOL for postmenopausal women with MS. Methods. We identified 251 Women's Health Initiative Observational Study participants with a self-reported MS diagnosis. Using a linear model, we estimated changes from baseline to 3 years for activities of daily living, total metabolic equivalent tasks (MET) hours per week, mental and physical component scales (MCS, PCS) of the SF-36, and menopausal symptoms adjusting for years since menopause and other confounders. Results. Nine percent were current and 50% past smokers. Age at smoking initiation was associated with significant changes in MCS during menopause. PCS scores were unchanged. While women who had ever smoked experienced an increase in physical activity during menopause, the physical activity levels of women who never smoked declined. Residual confounding may explain this finding. Smoking was not associated with change in menopausal symptoms during the 3-year follow-up. Conclusion. Smoking was not associated with health outcomes among post-menopausal women with MS.