Multiple sclerosis and motor neurone disease: survival and how certified after death

Asthma and chronic obstructive pulmonary disease (COPD) in people with multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

Studies have found that multiple sclerosis (MS) has an impact on the initiation or the course of asthma and chronic obstructive pulmonary disease (COPD). This review amied to investigate the prevalence and odds of asthma and COPD among people with MS (pwMS).

METHOD

PubMed, Embase, Scopus, and Web of Science were systemically searched from inception to May 2023. R version 4.3.2 and random-effect model were used to calculate the pooled prevalence and odds ratio (OR), with their 95 % confidence interval (CI), in pwMS.

RESULTS

A total of 40 studies consisting of 287,702 pwMS were included. 37 studies indicated that the pooled prevalences of asthma and COPD among pwMS were 5.97 % (95 % CI: 4.62 %-7.69 %, I2=99 %) and 3.03 % (95 % CI: 1.82 %-5.00 %, I2=99 %), respectively. 24 studies on 236,469 pwMS and 85,328,673 healthy controls revealed that the overall odds of asthma and COPD in MS were 1.14 (95 % CI: 0.76-1.71, p-value=0.53, I2=97 %) and 1.28 (95 % CI: 1.11-1.47, p-value<0.01, I2=70 %), respectively.

CONCLUSION

MS can increased the risk of developing COPD, while asthma does not exhibit a significant relationship with MS. Our study highlights the importance of identifying pwMS who face greater risks of respiratory issues to monitor efficiently and initiate suitable preventative actions.

Pre-diagnostic plasma urate and the risk of amyotrophic lateral sclerosis

OBJECTIVE

To prospectively examine for the first time the association between plasma urate levels measured in healthy participants and future amyotrophic lateral sclerosis (ALS) risk.

METHODS

A pooled case-control study nested in five US prospective cohorts comprising 319,617 participants who provided blood, of which 275 had ALS during follow-up. Pre-diagnostic plasma urate was determined for all participants using a clinical colorimetric enzyme assay. Gender-specific multivariable-adjusted rate ratios (RR) of ALS incidence or death estimated by conditional logistic regression and pooled using inverse-variance weighting.

RESULTS

In age- and matching factor-adjusted analyses, a 1 mg/dL increase in urate concentration was associated with RR = 0.88 (95% CI: [0.78, 0.997] p = 0.044). After adjustment for BMI, a strong predictor of ALS and urate levels, and other potential covariates, the RR = 0.89 (95% CI: [0.78, 1.02]; p = 0.08 for 1mg/dL increase in urate).

CONCLUSION

Elevation of plasma urate was modestly inversely associated with the risk of ALS and warrants further study for a potential role in this disease.

Effect of comorbidity on mortality in multiple sclerosis

Objective:

We aimed to compare survival in the multiple sclerosis (MS) population with a matched cohort from the general population, and to evaluate the association of comorbidity with survival in both populations.

Methods:

Using population-based administrative data, we identified 5,797 persons with MS and 28,807 controls matched on sex, year of birth, and region. We estimated annual mortality rates. Using Cox proportional hazards regression, we evaluated the association between comorbidity status and mortality, stratifying by birth cohort, and adjusting for sex, socioeconomic status, and region. We compared causes of death between populations.

Results:

Median survival from birth in the MS population was 75.9 years vs 83.4 years in the matched population. MS was associated with a 2-fold increased risk of death (adjusted hazard ratio 2.40; 95% confidence interval: 2.24–2.58). Several comorbidities were associated with increased hazard of death in both populations, including diabetes, ischemic heart disease, depression, anxiety, and chronic lung disease. The magnitude of the associations of mortality with chronic lung disease, diabetes, hypertension, and ischemic heart disease was lower in the MS population than the matched population. The most common causes of death in the MS population were diseases of the nervous system and diseases of the circulatory system. Mortality rates due to infectious diseases and diseases of the respiratory system were higher in the MS population.

Conclusion:

In the MS population, survival remained shorter than expected. Within the MS population, comorbidity was associated with increased mortality risk. However, comorbidity did not preferentially increase mortality risk in the MS population as compared with controls.

Respiratory dysfunction in multiple sclerosis

Respiratory dysfunction frequently occurs in patients with advanced multiple sclerosis (MS), and may manifest as acute or chronic respiratory failure, disordered control of breathing, respiratory muscle weakness, sleep disordered breathing, or neurogenic pulmonary edema. The underlying pathophysiology is related to demyelinating plaques involving the brain stem or spinal cord. Respiratory complications such as aspiration, lung infections and respiratory failure are typically seen in patients with long-standing MS. Acute respiratory failure is uncommon and due to newly appearing demyelinating plaques extensively involving areas of the brain stem or spinal cord. Early recognition of MS patients at risk for respiratory complications allows for the timely implementation of care and measures to decrease disease associated morbidity and mortality.

Dietary ω-3 polyunsaturated fatty acid intake and risk for amyotrophic lateral sclerosis

IMPORTANCE

Amyotrophic lateral sclerosis (ALS) is a severe progressive disease that cannot be prevented or cured. Diet-derived long-chain polyunsaturated fatty acids (PUFAs) are incorporated in brain lipids and modulate oxidative and inflammatory processes and could thus affect ALS risk and progression.

OBJECTIVE

To examine the association between ω-6 and ω-3 PUFA consumption and ALS risk.

DESIGN, SETTING, AND PARTICIPANTS

Longitudinal analyses based on 1,002,082 participants (479,114 women and 522,968 men) in 5 prospective cohorts: the National Institutes of Health-AARP Diet and Health Study, the Cancer Prevention Study II Nutrition Cohort, the Health Professionals Follow-up Study, the Multiethnic Cohort Study, and the Nurses' Health Study. Diet was assessed via food frequency questionnaire developed or modified for each cohort. Participants were categorized into cohort-specific quintiles of intake of energy-adjusted dietary variables.

MAIN OUTCOMES AND MEASURES

Cohort-specific multivariable-adjusted risk ratios (RRs) of ALS incidence or death estimated by Cox proportional hazards regression and pooled using random-effects methods.

RESULTS

A total of 995 ALS cases were documented during the follow-up. A greater ω-3 PUFA intake was associated with a reduced risk for ALS. The pooled, multivariable-adjusted RR for the highest to the lowest quintile was 0.66 (95% CI, 0.53-0.81; P < .001 for trend). Consumption of both α-linolenic acid (RR, 0.73; 95% CI, 0.59-0.89; P = .003 for trend) and marine ω-3 PUFAs (RR, 0.84; 95% CI, 0.65-1.08; P = .03 for trend) contributed to this inverse association. Intakes of ω-6 PUFA were not associated with ALS risk.

CONCLUSIONS AND RELEVANCE

Consumption of foods high in ω-3 PUFAs may help prevent or delay the onset of ALS.

Population-based epidemiology of amyotrophic lateral sclerosis (ALS) in an ageing Europe--the French register of ALS in Limousin (FRALim register)

BACKGROUND AND PURPOSE

The main objective of establishing the French register of amyotrophic lateral sclerosis (ALS) in the Limousin region (FRALim), was to assess the incidence of ALS, in this ageing region of Europe, over a 12-year period (2000-2011).

METHODS

Patients were included if they lived in Limousin at the time of diagnosis of ALS according to El Escorial revised criteria and were identified by at least one of the following sources: (i) the French national body coordinating ALS referral centres; (ii) public and private hospitals in the region; (iii) health insurance data related to long-term diseases.

RESULTS

The FRALim register identified 279 incident cases (2000-2011). The crude and European population standardized incidences of ALS were as high as 3.19/100,000 person-years of follow-up (95% CI 2.81-3.56) and 2.58/100,000 person-years of follow-up (95% CI 2.27-2.89) respectively. Median age at onset was 70.8 years (interquartile range 63.1-77.1). The standardized sex incidence ratio (male/female) was 1.3 overall, but 1.1 under the age of 65 years, 1.7 between 65 and 75 years and 1.9 above 75 years. The exhaustiveness of the register has been estimated at 98.4% (95% CI 95.6-99.4) by capture-recapture analysis.

CONCLUSION

It was possible for the first time in France to monitor accurately the incidence of ALS over a long time period. It appears to be in the upper range of data reported in western countries. Patterns displayed here might anticipate the epidemiology of ALS in ageing western countries.

Intakes of vitamin C and carotenoids and risk of amyotrophic lateral sclerosis: pooled results from 5 cohort studies

OBJECTIVE

Prior research has suggested the possible role of oxidative stress in the pathogenesis of amyotrophic lateral sclerosis (ALS). Prospective data examining dietary antioxidants such carotenoids and vitamin C are limited.

METHODS

Risk of ALS associated with carotenoid and vitamin C intake was investigated in 5 prospective cohorts: the National Institutes of Health-Association of American Retired Persons Diet and Health Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, the Health Professionals Follow-up Study (HPFS), and the Nurses Health Study (NHS). ALS deaths were documented using the National Death Index, and confirmed nonfatal ALS cases were included from HPFS and NHS. A total of 1,153 ALS deaths occurred among 1,100,910 participants (562,942 men; 537,968 women). Participants were categorized into cohort-specific quintiles of intake for dietary variables. We applied Cox proportional hazards regression to calculate cohort-specific risk ratios (RRs), and pooled results using random-effects methods.

RESULTS

A greater total major carotenoids intake was associated with a reduced risk of ALS (pooled, multivariate-adjusted RR for the highest to the lowest quintile = 0.75, 95% confidence interval [CI] = 0.61-0.91, p for trend = 0.004). Individually, higher dietary intakes of β-carotene and lutein were inversely associated with ALS risk. The pooled multivariate RRs comparing the highest to the lowest quintile for β-carotene and lutein were 0.85 (95% CI = 0.64-1.13, p for trend = 0.03) and 0.79 (95% CI = 0.64-0.96, p for trend = 0.01), respectively. Lycopene, β-cryptoxanthin, and vitamin C were not associated with reduced risk of ALS.

INTERPRETATION

Consumption of foods high in carotenoids may help prevent or delay onset of ALS.

Birth cohort effects in neurological diseases: amyotrophic lateral sclerosis, Parkinson's disease and multiple sclerosis

BACKGROUND

Generational differences in disease rates are the main subject of age-period-cohort (APC) analysis, which is mostly applied in cancer and suicide research. This study applied APC analysis to selected neurological diseases: amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and multiple sclerosis (MS).

METHODS

The analyses were based on Swiss mortality data. Age-stratified data has been available for MS, PD and ALS since 1901, 1921, and 1942, respectively. APC analysis was performed within the framework of logit models. Main effect models were extended by implementing nested effects, i.e. age effects nested in subperiods, in order to account for the fact that age profiles may change for reasons other than generational influences.

RESULTS

In preliminary analyses, APC analysis yielded noteworthy birth cohort effects in all three diseases. After implementing nested effects, the birth cohort effects disappeared in ALS, and smoothed out in PD, where they were greater for the generations born before the 1920s. In MS, the birth cohort effects remained stable, and exhibited a peak in cohorts born in the 1910s and 1920s.

CONCLUSIONS

APC analysis yielded some evidence for birth cohort effects, i.e. predisposing risk factors that may change in historical terms, in MS and PD, but probably not in ALS.

Smoking and risk of amyotrophic lateral sclerosis: a pooled analysis of 5 prospective cohorts

BACKGROUND

Cigarette smoking has been proposed as a risk factor for amyotrophic lateral sclerosis (ALS), but epidemiological studies supporting this hypothesis have been small and mostly retrospective.

OBJECTIVE

To prospectively examine the relation between smoking and ALS in 5 well-established large cohorts.

DESIGN

Five prospective cohorts with study-specific follow-up ranging from 7 to 28 years.

SETTING

Academic research.

PATIENTS

Participants in the Nurses' Health Study, the Health Professionals Follow-up Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, and the National Institutes of Health-AARP (formerly known as the American Association of Retired Persons) Diet and Health Study.

MAIN OUTCOME MEASURES

Amyotrophic lateral sclerosis deaths identified through the National Death Index. In the Nurses' Health Study and the Health Professionals Follow-up Study, confirmed nonfatal incident ALS was also included.

RESULTS

A total of 832 participants with ALS were documented among 562,804 men and 556,276 women. Smokers had a higher risk of ALS than never smokers, with age- and sex-adjusted relative risks of 1.44 (95% confidence interval, 1.23-1.68; P < .001) for former smokers and 1.42 (95% confidence interval, 1.07-1.88; P = .02) for current smokers. Although the risk of ALS was positively associated with pack-years smoked (P < .001), duration of smoking (9% increase for each 10 years of smoking, P = .006), and the number of cigarettes smoked per day (10% increase for each increment of 10 cigarettes smoked per day, P < .001), these associations did not persist when never smokers were excluded. However, among ever smokers, the risk of ALS increased as age at smoking initiation decreased (P = .03).

CONCLUSIONS

Results of this large longitudinal study support the hypothesis that cigarette smoking increases the risk of ALS. The potential importance of age at smoking initiation and the lack of a dose response deserve further investigation.

Vitamin E intake and risk of amyotrophic lateral sclerosis: a pooled analysis of data from 5 prospective cohort studies

The authors investigated whether vitamin E intake was associated with amyotrophic lateral sclerosis (ALS) in the Nurses' Health Study (1976-2004), the Health Professionals Follow-up Study (1986-2004), the Cancer Prevention Study II Nutrition Cohort (1992-2004), the Multiethnic Cohort Study (1993-2005), and the National Institutes of Health-AARP Diet and Health Study (1995-2005). ALS deaths were identified through the National Death Index. In the Nurses' Health Study and the Health Professionals Follow-up Study, confirmed nonfatal ALS cases were also included. Cohort-specific results were estimated using Cox proportional hazards models and pooled using random-effects models. Among 1,055,546 participants, 805 developed ALS. Overall, using vitamin E supplements was not associated with ALS. However, within cohorts with information on duration of vitamin E supplement use (231 cases), ALS rates declined with increasing years of use (P-trend=0.01). Compared with nonusers, the multivariable-adjusted relative risk was 1.05 (95% confidence interval (CI): 0.60, 1.84) among users for ≤1 year (12 cases), 0.77 (95% CI: 0.33, 1.77) among users for 2-4 years (7 cases), and 0.64 (95% CI: 0.39, 1.04) among users for ≥5 years (18 cases). For dietary vitamin E intake, the multivariable-adjusted relative risk comparing the highest quartile with the lowest was 0.79 (95% CI: 0.61, 1.03); an inverse dose-response was evident in women (P-trend=0.002) but not in men (P-trend=0.71). In this large, pooled prospective study, long-term vitamin E supplement use was associated with lower ALS rates. A possible protective effect of vitamin E deserves further consideration.

Validating population-based registers for ALS: how accurate is death certification?

The purpose of this study was to determine the accuracy of death certification for amyotrophic lateral sclerosis (ALS)/motor neuron disease (MND) as recorded by the Central Statistics Office in the Republic of Ireland, and to examine its utility in capture-recapture analysis. The database of the Irish Central Statistics Office (CSO) was searched for death certificates of individuals over 15 years of age for whom ALS/MND (ICD9) was listed as a primary, secondary or tertiary cause of death from 2002 to 2006. This dataset was compared with mortality data from the Irish Register for ALS/MND for the same period. Three hundred ninety-eight cases with a diagnosis of ALS were identified through the CSO. The cause of death as identified by the CSO was 318 out of 398 (80%) cases known to the Register during the study period. ALS/MND was listed as a cause of death by the CSO in 79 (20%) cases that were unknown to the ALS/MND Register. Of these, ALS/MND was listed as a secondary/tertiary cause of death in 76, and 75% of all such deaths occurred in rural areas. Capture-recapture analysis using the CSO and ALS Register as independent datasets generated a likely over-estimation of the crude incidence of ALS from 2.1/100,000 to 3.45/100,000 in Ireland. Population-based registers are most accurate when ascertaining from a wide network of inter-dependent sources. Death certification for ALS/MND lacks both sensitivity and specificity. Capture-recapture exercises using such data sources are likely to over-estimate the true incidence of disease.

Mortality in multiple sclerosis: a review

This work was undertaken to evaluate studies on mortality caused by multiple sclerosis (MS), to evaluate if useful inferences can be drawn from survival studies that can be applied to clinical practice. A literature search was carried out to find epidemiological studies on MS prognosis, survival, mortality and causes of death relevant to our aim. The World Health Organization (WHO) reports on worldwide cause-specific mortality were also considered. Studies were evaluated according to the duration of the follow-up study, the year of publication and the methodology used. We evaluated MS survival from a methodological point of view and considered if time trends could be drawn from study results. We conclude that mortality is only slightly higher in MS patients when compared with that in the general population. Mortality is higher particularly for older patients and those with longer disease duration.

Childhood infection and adult disease

In England and Wales there is a strong geographical relation between current mortality from chronic bronchitis and emphysema in adults and infant mortality from bronchitis and pneumonia 50 years ago. Follow-up studies of infants and children show that certain pulmonary infections cause persisting abnormalities of lung function. This suggests that infection of an organ system during a period of rapid growth may have permanent deleterious effects. Long-term consequences of infection may also depend on age-related differences in the host response. The relationship between age of infection with hepatitis B virus and the likelihood of becoming a chronic HBsAg carrier is an example of this. Evidence that the common communicable diseases of childhood tend to have occurred late in cases of multiple sclerosis hints at similar mechanisms in this disease. The current patterns of motor neuron disease mirror the epidemiology of poliovirus infection 40 years ago both in geographical distribution and in changes over time. The same neuronal populations are affected in both these conditions; is there a causal link?

Geographic distribution of amyotrophic lateral sclerosis through motor neuron disease mortality data

Amyotrophic lateral sclerosis (ALS) is a rare and devastating neurological disorder of the adult age with a prognosis of about 2-3 years from the onset of the disease. No clear cause has been identified but it seems to be a multifactorial disease with genetic and environmental components involved. Increments of mortality rates were observed since 1980 both in Italy and in many other countries. The objective of the present study is to describe the distribution of ALS mortality in Italy in the period 1980-2001 detecting single municipalities or clusters with high mortality levels for motor neuron disease (MND). ALS represents the main part (85%) of the MND group which is globally identified by the IX ICD (International Classification of Diseases and Causes of Death) 335.2 code. Death numbers and standardized mortality ratios (SMR) for MND were calculated for all Italian municipalities through the ENEA mortality database system (data source: National Institute of Statistics-ISTAT), using national mortality rates as reference. Subsequently, in order to detect municipal clusters, spatial analysis was performed. Out of the 8,099 Italian municipalities, 132 where characterized by SMR values higher than expected. Moreover 16 clusters with significant high relative risk values (RR) were identified, 12 out of them including only a single municipality. Only 22 of the municipalities with high SMR were included in the clusters. In conclusion, the two different epidemiological methodologies demonstrated to be widely complementary in detecting the geographical distribution of the disease in terms of risk for populations. A first selection of the priority areas where analytical studies should be carried on, in order to identify risk factors associated to ALS, is tentatively suggested.

Prospective study of occupation and amyotrophic lateral sclerosis mortality

Occupational exposures are suspected of contributing to the risk of amyotrophic lateral sclerosis (ALS), but results of epidemiologic studies have been inconsistent. The authors prospectively assessed the relation between occupation and ALS mortality among more than 1 million participants in the Cancer Prevention Study II of the American Cancer Society. Follow-up from 1989 through 2002 identified 507 ALS deaths among men and 430 among women. Adjusted rate ratios were calculated by using Mantel-Haenszel weights and Cox proportional hazards. Among men, elevated ALS mortality was found for programmers (rate ratio = 4.55, 95% confidence interval: 1.46, 14.2; p = 0.009) and laboratory technicians (rate ratio = 1.96, 95% confidence interval: 1.04, 3.66; p = 0.04). Occupations previously associated with increased risk of ALS for which no increased risk was found included farmers, electricians, and welders, although the numbers of electricians (eight ALS deaths) and welders (two ALS deaths) were small. Among women, only machine assemblers had significantly increased ALS mortality (rate ratio = 2.81, 95% confidence interval: 1.05, 7.53; p = 0.04). Results, which suggest that male programmers and laboratory technicians and female machine assemblers may be at increased risk of death from ALS, should be interpreted cautiously, however, because they are based on small numbers.

Vitamin E intake and risk of amyotrophic lateral sclerosis

Oxidative stress may contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS). We therefore examined prospectively whether individuals who regularly use supplements of the antioxidant vitamins E and C have a lower risk of ALS than nonusers. The study population comprised 957,740 individuals 30 years of age or older participating in the American Cancer Society's Cancer Prevention Study II. Information on vitamin use was collected at time of recruitment in 1982; participants then were followed up for ALS deaths from 1989 through 1998 via linkage with the National Death Index. During the follow-up, we documented 525 deaths from ALS. Regular use of vitamin E supplements was associated with a lower risk of dying of ALS. The age- and smoking-adjusted relative risk was 0.99 (95% confidence interval [CI], 0.69-1.41) among occasional users, 0.59 (95% CI, 0.36-0.96) in regular users for less than 10 years, and 0.38 (95% CI, 0.16-0.92) in regular users for 10 years or more as compared with nonusers of vitamin E (p for trend = 0.004). In contrast, no significant associations were found for use of vitamin C or multivitamins. These results suggest that vitamin E supplementation could have a role in ALS prevention.

[Recording of multiple sclerosis in Swiss cause of death statistics. A 10-year mortality follow-up of the Bern prevalence study]

Based on data from a multiple sclerosis (MS) prevalence study which had been carried out in 1986 in the canton of Berne, Switzerland, a follow-up was performed 10 years later to gather information on mortality in the original study population. The authors used information on residency and death as gathered from municipal offices and, additionally, by record-linkage with the Swiss cause of death statistics. Slightly more than 80% of the cases were identified unequivocally as of January 1996. Among them, 21% of the cases died during the ten-year period; 70% of them have an MS entry in the cause of death statistics, mostly as the main cause of death. A large proportion of the non-identifiable cases appear to be related to mortality; thus, the findings here do not provide a promising basis for certain further analyses. In conclusion, continuous updating of personal data is the only way to avoid loss to follow-up in the carefully assembled prevalence database.

Motor neurone disease in South Estonia. Diagnosis and incidence rate

The current study evaluated the diagnostic standards of MND and epidemiological markers of MND in Estonia. A total of 108 patients were referred to the University Hospital from 1986 to 1995 with the first suggested diagnosis or final diagnosis of amyotrophic syndrome, amyotrophic lateral sclerosis (ALS), progressive bulbar paralysis (PBP) or progressive muscular atrophy (PMA). In addition neurologists of the region and the National Society of Neuromuscular disorders were contacted. Some 94 patients satisfied the diagnostic criteria. The annual incidence rate in South Estonia and in the city of Tartu ranged from 0.5 to 2.8 per 100,000. The mean annual incidence rate in Tartu is 1.98 and in South Estonia in general 1.3. The highest incidence rate was 8.3 for men in the age group 60 to 64 years and 7.49 in the age group 70-74; among female patients the highest incidence rate -4.6 was in the age group from 65 to 69.

Underlying cause of death in Danish patients with multiple sclerosis: results from the Danish Multiple Sclerosis Registry

OBJECTIVES

To determine the underlying causes of death in a large population based register series of patients with multiple sclerosis.

METHODS

The Danish Multiple Sclerosis Registry, which contains virtually all diagnosed cases of multiple sclerosis in Denmark who were alive in 1949 plus cases with onset of multiple sclerosis in the period 1949-93, who have been diagnosed and notified by 1 January 1994, was linked with the Danish Registry of Causes of Death, in which ICD codes for causes of death from the death certificate are stored for all Danish citizens.

RESULTS

6068 register cases of multiple sclerosis, who had died in the period 1951-93, were included. Multiple sclerosis was noted on the death certificate as the underlying cause of death in 55.4%; cardiac or vascular diseases in 17.6%; cancers in 8.6%; respiratory or infectious diseases in 5.1%; other natural causes in 9.5%; accident or suicide in 3.8%. The distribution varied with age at death. Standardised mortality ratios (SMRs) were computed on the basis of the 8142 incident cases, who had onset of multiple sclerosis within the period 1951-93; the SMRs for causes of death other than multiple sclerosis were highest for infectious or pulmonary diseases: 2.46 (95% confidence interval (95% CI) 2.04-2.94); suicide: 1.62 (95% CI 1.29-2.01); cardiac or vascular diseases: 1.34 (95% CI 1.22-1.48); accidents 1.34 (95% CI 1.02-1.71); and significantly lower than unity for cancers: 0.79 (95% CI 0.70-0.90), lower for men than for women.

CONCLUSIONS

More than half of the patients with multiple sclerosis die from multiple sclerosis or complications of the disease. Among other causes, patients with multiple sclerosis have an increased risk of dying from heart or vascular diseases but a reduced risk of dying from cancer. An increased risk of death from suicide and accidents can be indirectly attributed to multiple sclerosis. The diminished risk of dying from cancer may be a result of incomplete ascertainment of cancers in disabled patients with multiple sclerosis.

British motor neuron disease twin study

OBJECTIVES

To investigate the cause of sporadic motor neuron disease (MND) by twin study, so allowing (1) estimation of the genetic contribution, and (2) collection of matched pairs for a case-control study of possible environmental factors.

METHODS

10872 death certificates bearing the diagnosis MND were collected from 1979 to 1989 inclusive. Inspection of individual birth entries allowed identification of potential twins. The status of each co-twin was determined and contact made through the National Health Service Central Register (NHS-CR) and their general practitioner (GP). The diagnosis of MND was verified via the co-twin and relatives, and medical records where available. Zygosity was assessed using a recognised questionnaire. Details concerning environmental exposures and health were gathered by interview of cotwin and relatives using a semistructured questionnaire. Heritability (h2) of MND was estimated, and the environmental information was analysed by conditional logistic regression modelling.

RESULTS

Seventy seven probands were identified, of whom 26 were monozygotic and 51 dizygotic. Four monozygotic probands were concordant, but two probands came from a family known to have familial MND. The estimated heritability was between 0.38 and 0.85. Most environmental risk factors were not significant. Regular vehicle maintenance (odds ratio (OR) = 7.0; 95% confidence interval (95% CI) 1.3-89.9) and occupational paint usage (OR = 3.75; 95% CI 1.0-17.1), however, occurred significantly more often in the affected cases.

CONCLUSIONS

This "death discordant" method for twin collection has proved to be viable, and has allowed the ascertainment of a large population sample in a rare disease. The genetic role in sporadic MND is substantial, and higher than expected. Exposure to industrial chemicals, particularly constituents of petrochemicals and paints, may contribute to the aetiology of MND.

Clinical epidemiology of amyotrophic lateral sclerosis

The introduction of palliative therapies in amyotrophic lateral sclerosis (ALS) will alter the epidemiology of ALS as it is known now. Although incidence rates will remain unchanged in the near future, prevalence rates will likely increase dramatically. Better understanding of the age-specific presentation of motor neuron diseases worldwide will shed light on the vexing questions concerning the variable incidence rates in some countries and apparent incidence gradients in North America and Europe.

Ecological correlates of motor neuron disease mortality: a hypothesis concerning an epidemiological association with radon gas and gamma exposure

This study investigates variations in motor neuron disease (MND) mortality rates between the counties of England and Wales from 1981 to 1989, and their relationship with gamma-ray dose rates, indoor radon gas concentrations and enhanced general life expectancy. A strong correlation was confirmed between age-adjusted rates of MND mortality and life expectancy. Weaker, but statistically significant, associations were observed between indoor radon gas concentrations, terrestrial gamma radiation and marginal variations in MND mortality. Life expectancy and radon gas concentrations were positively associated with MND mortality rates whilst gamma radiation was negatively associated. The negative correlation of gamma radiation with MND mortality may be understood with reference to its negative effects on overall population life expectancy. Radon gas concentrations seemingly account for a small elevation in MND mortality, amounting to at most 4% of total deaths. Further research is required to investigate this association.

Mortality from motor neuron disease in Japan, 1950-1990: association with radioactive fallout from atmospheric weapons testing

Motor neuron disease (MND) is a progressive and invariably fatal disease affecting the nuclei of the pyramidal tract and anterior horn cells. Despite intensive research into environmental agents associated with the onset or course of the disease, there is no single factor that can be confidently linked over time with regional, national or international variations in mortality rates. However, unusual variations in MND mortality rate in Japan from 1950-1990 were found to correlate highly significantly with variations in radioactive fallout released by atmospheric weapons testing in the Pacific. This association could be explained by the ingestion of alpha-emitting radionuclides acting upon a pre-existing susceptible subpopulation, a hypothesis which is consistent with recent research on the epidemiology and pathology of MND. However, it is likely that radiation is only one of many factors that act singly or in combination to accelerate the condition in subpopulations susceptible to MND.

Rising mortality from motor neurone disease in Sweden 1961-1990: the relative role of increased population life expectancy and environmental factors

Recent studies of mortality from motor neurone disease (MND) in Sweden have demonstrated rising levels of mortality from the disease, especially amongst older age groups. Case-control investigations have suggested that certain environmental factors are significantly related to variations in mortality from the disease, and are associated with a probable individual susceptibility to MND. This study applies an innovative epidemiological technique to longitudinal and cohort analysis of Swedish mortality from MND during the period 1961 to 1990. Survival modelling shows that a subpopulation susceptible to MND exists in Sweden, as has been demonstrated in other countries. The increased life expectancy of the Swedish population since 1961 has resulted in more of that susceptible population living to the ages at which MND is expressed, explaining the majority of the increase in mortality from the disease. However, environmental factors may play a role in accelerating the course of MND and may affect the timing of death within the susceptible sub-population.

Rising amyotrophic lateral sclerosis mortality in France 1968-1990: increased life expectancy and inter-disease competition as an explanation

Gompertzian analysis is a statistical technique which has been successfully applied to the analysis of amyotrophic lateral sclerosis (ALS) mortality in England and Wales, Japan and the United States. This paper analyses the consistent trend of rising ALS mortality in France over the years 1968-1990, a period during which crude mortality rose from 400 deaths in 1968 to 950 deaths in 1990. The findings indicate that age-specific mortality rates have risen at ages older than 54 years for men and 53 years for women and decreased slightly at younger ages. The evolving ALS mortality pattern is attributable to changing inter-disease competition resulting from the increased life expectancy of the French population, rather than to changing environmental aetiopathogenic factors or to substantial artefact effects.

Reinterpreting mortality statistics: some uses of Gompertzian analysis in epidemiological research

Gompertzian analyses of mortality data have recently been undertaken for a number of individual conditions (Riggs JE. Mech Ageing Dev 1990; 55: 207-220 [1]; Neilson S et al. Mech Ageing Dev 1992; 64: 201-216 [2]; Neilson S et al. Acta Neurol Scand 1993; 87: 184-191 [3]). Such analyses are in principle of particular epidemiological value in circumstances where demographic change is occurring and where the balance between mortality from different conditions is subject to change. However, the extent to which a Gompertzian relationship between age and mortality holds for particular conditions has been subject to debate. In this analysis it is demonstrated that even some conditions which do not superficially hold to a Gompertz relationship do in fact do so, if such conditions are considered to be restricted to small, inherently susceptible subpopulations. By analysing mortality from a range of neurological conditions within the context of general mortality in England and Wales, conditions with different aetiologies such as Huntington's chorea, amyotrophic lateral sclerosis and multiple sclerosis can be shown to have a Gompertzian mortality rate distribution. Such analyses are of substantial value in indicating how demographic change affects the balance of mortality between conditions, as well as directing interest to revised aetiological possibilities.

A new analysis of mortality from motor neurone disease in Japan, 1950-1990: rise and fall in the postwar years

Recent studies have demonstrated a worldwide rise in mortality from motor neurone disease (MND). However, in Japan mortality appears to have fallen significantly since the late 1960s, especially amongst women. Studies of the cause of both the worldwide rise, and the unique decline in MND mortality in Japan, have largely failed to substantiate the role of any single factor, or group of factors in these phenomena. Modelling the relationship between age and mortality using gompertzian analysis has already shown that the rise in MND mortality in England and Wales, and the United States, is mainly the result of increased longevity and decreasing competition from other causes of death amongst a susceptible subpopulation. Employing the same techniques on Japanese mortality data from 1950 to 1990 demonstrates that an unusual and accelerated increase of mortality occurred in the 1950s and 1960s, probably caused by an earlier unknown but extremely potent environmental agent or agents. This premature depletion of the susceptible subpopulation resulted subsequently in a lower than expected mortality rate. Mortality is now rising slowly to expected levels as the size of the susceptible subpopulation recovers to reach the ages at which MND is normally expressed. Further substantial rises in mortality are anticipated in future decades.

Motor neuron disease and multiple sclerosis mortality in Australia, New Zealand and South Africa compared with England and Wales

There has been a marked increase in the reported mortality from motor neuron disease (MND) but not multiple sclerosis (MS) in England and Wales and in a number of other countries. A comparison has been made of the mortality from MND and from MS for two time periods in Australia, New Zealand and South Africa. An increase in MND mortality occurred in Australia and New Zealand between 1968-77 and 1978-87, greater than that which occurred in England and Wales, but there was no increase in MS mortality. Among the white population of South Africa, the MND mortality was half of that in England and Wales, Australia and New Zealand in both time periods. Both MND and MS mortality is higher in the English-speaking than in the Afrikaans-speaking white South African-born. The marked increase in MND mortality which has now been reported from many countries, is good evidence that an environmental factor is important in causing this disease. The large differences in MND mortality in different populations may be important clues to the environment factors causing the disease.

Utility of Scottish morbidity and mortality data for epidemiological studies of motor neuron disease

OBJECTIVES

To determine the accuracy of (1) hospital discharge data and (2) death certificates, coded as motor neuron disease (MND).

DESIGN

Comparison of data from The Scottish Motor Neuron Disease Register (SMNDR) with routinely collected Scottish Hospital In-Patient Statistics (SHIPS) and death certificate coding.

SETTING

Scotland UK.

PATIENTS

1) 379 adults (> 15 years) discharged for the first time from a Scottish hospital in 1989-90 and (2) 281 deaths in the same period assigned to the International Classification of Diseases (ICD)-9, category 335 (MND).

MAIN OUTCOME MEASURES

The sensitivity and positive predictive value of a diagnosis of MND as retrieved by (1) the Information and Statistics Division of the Common Services Agency for the Scottish Health Service for morbidity data and (2) the Registrar General's office for mortality data, using the SMNDR as the 'gold standard'.

RESULTS

(1) Thirty per cent of adult patients identified as having MND by SHIPS did not have this disease and 23% of patients with MND did not appear on SHIPS. The sensitivity of a diagnosis of MND, as retrieved by SHIPS, was 84% and the positive predictive value was 70% overall. Miscoding of patients with pseudobulbar palsy caused by cerebrovascular disease was the major source of false positive error. The incidence of adult onset sporadic MND was over estimated by SHIPS by a factor of 1.6. (2) Mortality data were more accurate, with a false negative rate of 6% and a positive predictive value of 90%.

CONCLUSIONS

Coded hospital discharge data are an inaccurate record of a diagnosis of MND and cannot, in their present form, be used as a reliable measure of disease incidence in Scotland. Greater care is required in the preparation of discharge summaries and coding if these data are to be useful for health care planning and epidemiological research. SHIPS is, however, an important source of information to achieve a complete sample of patients with MND. There is also a problematic false positive rate for mortality data but this source more closely approximates true incidence.

Rising mortality from motor neurone disease: an explanation

There is considerable debate about the increasing mortality from motor neurone disease (MND). However, examination of the relationship between increased life expectancy (through decreased general mortality) and increased mortality in both England and Wales and the United States indicates a close association between the two variables. Using a statistical model, defined sub-populations susceptible to MND can be identified in both countries. The size of such a sub-population has been estimated from the 1989 mortality data to be approximately 160,000 people in England and Wales. The proportion of this sub-population dying from MND has increased over the last 30 years, rather than, as previously, dying at an earlier age from other conditions. On this basis, deaths from MND are expected to increase by a further 20% in this sub-population between 1991-2021 because of continuing changes in life expectancy. MND is a condition made increasingly visible in mortality statistics through decreased general mortality, rather than one in which the underlying population at risk has substantially changed. Aetiological extrapolations from the data indicate that susceptibility to the disease is acquired early in life, and that it is unlikely, given the relative stability of the underlying sub-population, that either changed environmental circumstances or artifactual factors can account in themselves for the rise in mortality.

Static and dynamic models of interdisease competition: past and projected mortality from amyotrophic lateral sclerosis and multiple sclerosis

Longitudinal Gompertzian analysis is an effective method for determining both the pure probability of death for a given condition and the size of inherently susceptible subpopulations [1]. Gompertzian analysis has been used in this study to provide the parameters necessary to construct a stationary population lifetable (static model) of mortality for amyotrophic lateral sclerosis (ALS) and for multiple sclerosis (MS). The static model demonstrates the relative effect of changing general mortality upon the mortality from each specific disease in a situation where interdisease competition is continuously changing. In order to represent mortality in a real population more closely (where age structure is not the result of mortality rates alone) a dynamic model was constructed for both conditions using the age distributions of the population of England and Wales. The quality of the model was verified by comparison of estimated mortality with historical data from the last three decades. The dynamic model has then been used to estimate mortality from each condition over the next three decades on the basis of population projections made by the Central Statistical Office [2], assuming no major change in the factors which lead to either condition. This analysis demonstrates both the theoretical applicability and practical capabilities of Gompertz-derived mortality models for analysing changing mortality patterns.

Motor neuron disease and polio in Scotland

An analysis of mortality and morbidity rates for motor neuron disease (MND) in Scotland has confirmed earlier observations that the disease is more common in men and older age groups. The geographical distribution is non-uniform and related to discharge rates for all neurological diseases. Discharge and mortality rates are increasing but there has been no decline in populations who would have been vaccinated against polio.

Adult onset motor neuron disease: worldwide mortality, incidence and distribution since 1950

This review examines the commonly held premise that, apart from the Western Pacific forms, motor neuron disease (MND), has a uniform worldwide distribution in space and time; the methodological problems in studies of MND incidence; and directions for future epidemiological research. MND is more common in men at all ages. Age-specific incidence rises steeply into the seventh decade but the incidence in the very elderly is uncertain. A rise in mortality from MND over recent decades has been demonstrated wherever this has been examined and may be real rather than due to improved case ascertainment. Comparison of incidence studies in different places is complicated by non-standardised methods of case ascertainment and diagnosis but there appear to be differences between well studied populations. In developed countries in the northern hemisphere there is a weak positive correlation between standardised, age-specific incidence and distance from the equator. There is now strong evidence for an environmental factor as the cause of the Western Pacific forms of MND. A number of clusters of sporadic MND have been reported from developed countries, but no single agent identified as responsible.

Accuracy of death certificate diagnosis of amyotrophic lateral sclerosis

STUDY OBJECTIVE

The aim was to determine the reliability of official mortality statistics in estimating long term trends of amyotrophic lateral sclerosis (ALS) in Italy.

DESIGN

The study was a mortality follow up of cases of ALS.

SETTING

Piedmond Region, northern Italy.

SUBJECTS

Cases of ALS were identified from multiple sources between 1966 and 1985.

MAIN RESULTS

Cause of death was determined for the cases who died between 1970 and 1985. Death certificates were obtained in 488 out of 510 cases (95.7%). ALS was mentioned in 365 (74.8%) of cases. The most frequent erroneous diagnoses were multiple sclerosis and malignant tumours. Demographic variables, such as sex, age at death, province of death, and calendar year of death, did not influence the percentage of true positive cases significantly.

CONCLUSIONS

The death certificate diagnosis of ALS appears to be adequate for use in descriptive and analytical epidemiology.

Longitudinal Gompertzian analysis of ALS mortality in England and Wales, 1963-1989: estimates of susceptibility in the general population

Mortality statistics in amyotrophic lateral sclerosis (ALS), which is more commonly and generally termed motoneurone disease (MND) in the United Kingdom, have been shown to reflect the incidence of previously diagnosed cases of the disease in a more complete way than in other conditions [1,2]. An analysis of changing patterns of mortality may therefore be a particularly appropriate way of tracing the underlying trends in the disease and is in principle a useful way of investigating the relationship between environmental and genetically controlled factors in the genesis of the condition. The majority of analyses so far have concentrated on the crude rise in reported mortality rates evident in recent decades in a number of countries [2-5], on the uneven geographical distribution [6,7] and on the complex range of plausible causes for these reported rises. Debates have centred on whether the increases represent 'real' or 'artifactual' changes, with no apparent resolution of the issue [8,3]. Recently Riggs [9] proposed a novel way of analysing this issue by using a Gompertzian model and provided evidence of the existence of an inherently susceptible subset of the US population. Riggs indicated that while the rise in ALS mortality is real, it is for the most part the result of an increase in the size of this inherently susceptible sub-population due to greater longevity. In order to examine the wider applicability of a Gompertzian model to ALS the technique has been replicated with the mortality rates for England and Wales for the 27-year period from 1963 to 1989. The technique has been developed and extended to produce an estimate of the size of the inherently susceptible sub-population (both male and female) over the entire period.

Do nurses or doctors have an increased risk of developing multiple sclerosis?

A cluster of multiple sclerosis (MS) patients has been reported in seven of 307 nurses in Key West, Florida. The MS death rates in British nurses and qualified medical practitioners were looked at and no increased mortality from multiple sclerosis was found. Neither was there an increase in mortality from motor neuron disease (amyotrophic lateral sclerosis), the control disease. Death rates from MS vary with social class, being highest in social class IIIN (skilled non-manual) and lowest in social class II (intermediate). These different rates may be due to MS causing health related occupational mobility. Allowance for the inter-class variability in MS death rates did not materially affect the conclusion that death from MS appears to be no more common than expected among nurses and doctors than in the general population. Possible explanations for the cluster of multiple sclerosis among nurses in Key West are discussed.

The contribution of mortality statistics to the study of multiple sclerosis in Australia

Mortality statistics provided a valuable source of support for data obtained from prevalence surveys of multiple sclerosis in Australia. Firstly, multiple sclerosis mortality data for the decade 1971-80 in the States of Australia confirmed the relationship between increasing disease frequency and increasing south latitude shown by State and regional point prevalence surveys based on the national census day 30 June 1981. Secondly, a comparison with mortality data from the decade 1950-59 showed that in most States there had been a substantial fall in multiple sclerosis mortality in the more recent decade and this was clearly an important contributing factor to the rise in prevalence noted between the morbidity surveys of 1961 and 1981. Thirdly, multiple sclerosis mortality in the UK-born migrant population dying in Australia was found to be similar to that of the Australian-born population and very much lower than that found in the UK. This observation corroborated evidence from the 1981 morbidity surveys and suggested that migration from the UK to Australia may lower the risk of developing multiple sclerosis either through a reduction in disease incidence or the operation of environmental factors curbing disease expression.

Motoneuron disease and past poliomyelitis in England and Wales

Past notification rates for poliomyelitis show a close geographical relation with current mortality from motoneuron disease in England and Wales. The increasing rate of poliomyelitis during the first half of this century and its predilection for affluent places and families were unique amongst infectious diseases. The unusual epidemiology of poliomyelitis is now being paralleled by motoneuron disease. These observations provide new evidence for a causal connection between the two conditions.