Severe head injury and amyotrophic lateral sclerosis

Risk factors associated with amyotrophic lateral sclerosis based on the observational study: a systematic review and meta-analysis

Objective

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder affecting the upper and lower motor neurons. Though the pathogenesis of ALS is still unclear, exploring the associations between risk factors and ALS can provide reliable evidence to find the pathogenesis. This meta-analysis aims to synthesize all related risk factors of ALS to understand this disease comprehensively.

Methods

We searched the following databases: PubMed, EMBASE, Cochrane library, Web of Science, and Scopus. Moreover, observational studies, including cohort studies, and case-control studies, were included in this meta-analysis.

Results

A total of 36 eligible observational studies were included, and 10 of them were cohort studies and the rest were case-control studies. We found six factors exacerbated the progression of disease: head trauma (OR = 1.26, 95% CI = 1.13, 1.40), physical activity (OR = 1.06, 95% CI = 1.04, 1.09), electric shock (OR = 2.72, 95% CI = 1.62, 4.56), military service (OR = 1.34, 95% CI = 1.11, 1.61), pesticides (OR = 1.96, 95% CI = 1.7, 2.26), and lead exposure (OR = 2.31, 95% CI = 1.44, 3.71). Of note, type 2 diabetes mellitus was a protective factor for ALS. However, cerebrovascular disease (OR = 0.99, 95% CI = 0.75, 1.29), agriculture (OR = 1.22, 95% CI = 0.74, 1.99), industry (OR = 1.24, 95% CI = 0.81, 1.91), service (OR = 0.47, 95% CI = 0.19, 1.17), smoking (OR = 1.25, 95% CI = 0.5, 3.09), chemicals (OR = 2.45, 95% CI = 0.89, 6.77), and heavy metal (OR = 1.5, 95% CI = 0.47, 4.84) were not risk factors for ALS based on meta-analyses.

Conclusions

Head trauma, physical activity, electric shock, military service, pesticides, and lead were risk factors for ALS onset and progression. But DM was a protective factor. This finding provides a better understanding of ALS risk factors with strong evidence for clinicians to rationalize clinical intervention strategies.

INPLSY registration number

https://inplasy.com/inplasy-2022-9-0118/, INPLASY202290118.

[Physical performance in patients with amyotrophic lateral sclerosis and its relationship with wheelchairs and walking aids use]

INTRODUCTION AND OBJECTIVES

Gait deficits and falls in patients with amyotrophic lateral sclerosis (ALS) restrict mobility. The aim of this study is to examine the appropriate use of walking aids and wheelchairs, based on the risk of falling and walking speed of patients with ALS.

METHODS

Retrospective data from patients from the ALS clinic were included. Age, gender, evolution time, wheelchair use, walking aids, gait speed and the Berg Balance Scale were registered. Categorical variables were related to the Chi Square test and Fisher's exact test.

RESULTS

Fifty eight patients met the inclusion criteria. Twenty-seven (46.55%) had adequate use of a wheelchair based on walking speed (p=.50). This association decreases to 6% in patients who walked at a speed lower than 0.88m/s. Forty-two (70.69%) had adequate use of an assistive device based on the risk of falls (p=.001). Of the subgroup with Berg Balance score ≤ 45, 38% did not use the appropriate device (p=.06).

CONCLUSION

Patients with severe gait and balance deficits had inappropriate use of walking aids and/or wheelchairs. The findings of this study may mean a contribution that could be considered in the clinical evaluations of patients with ALS to minimize risks and improve the participation of this group of people.

Environmental risk factors for amyotrophic lateral sclerosis: a case-control study in Canada and France

Objective: To evaluate the association between amyotrophic lateral sclerosis (ALS) and potential environmental risk factors, especially head traumas and pesticides, in two populations from Canada and France.Methods: A case-control study was performed in tertiary-care centers. Consecutive ALS cases were recruited along with a control group from the same age distribution and region. Participants answered a phone-administered questionnaire. Head trauma exposure was censored at age of symptom onset, and a sensitivity analysis considering old head traumas that occurred more than 3 years before onset was performed. Univariate and multivariate logistic regression were used to estimate odds ratios (ORs) and their 95% confidence intervals (CIs).Results: A total of 404 ALS cases and 381 controls completed the questionnaire. Previous head trauma was more frequently reported by cases (adjusted OR 1.50 (1.05-2.18)) with a dose-response relationship. This association was driven by a strong effect in men (adjusted OR 2.06 (1.22-3.55)) and was consistent for old traumas, but there was no association in women. For pesticides, a previous high-risk occupation was associated with ALS (adjusted OR 2.08 (1.36-3.24)), although reported occupational exposure to pesticides was not statistically significant in the multivariate model (adjusted OR 1.67 (0.97-2.97)). Past electrocution was associated with ALS (adjusted OR 1.79 (CI 1.13-2.87)), especially spinal-onset ALS. Residential exposure to pesticides, neck trauma, and welding were not associated with ALS.Conclusions: Head trauma is a risk factor for ALS in men only. Previous occupation at high risk for pesticides exposure and electrocution are also risk factors for ALS.

Traumatic injury compromises nucleocytoplasmic transport and leads to TDP-43 pathology

Traumatic brain injury (TBI) is a predisposing factor for many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), and chronic traumatic encephalopathy (CTE). Although defects in nucleocytoplasmic transport (NCT) is reported ALS and other neurodegenerative diseases, whether defects in NCT occur in TBI remains unknown. We performed proteomic analysis on Drosophila exposed to repeated TBI and identified resultant alterations in several novel molecular pathways. TBI upregulated nuclear pore complex (NPC) and nucleocytoplasmic transport (NCT) proteins as well as alter nucleoporin stability. Traumatic injury disrupted RanGAP1 and NPC protein distribution in flies and a rat model and led to coaggregation of NPC components and TDP-43. In addition, trauma-mediated NCT defects and lethality are rescued by nuclear export inhibitors. Importantly, genetic upregulation of nucleoporins in vivo and in vitro triggered TDP-43 cytoplasmic mislocalization, aggregation, and altered solubility and reduced motor function and lifespan of animals. We also found NUP62 pathology and elevated NUP62 concentrations in postmortem brain tissues of patients with mild or severe CTE as well as co-localization of NUP62 and TDP-43 in CTE. These findings indicate that TBI leads to NCT defects, which potentially mediate the TDP-43 pathology in CTE.

Head Injury and Amyotrophic Lateral Sclerosis: A Meta-Analysis

BACKGROUND

Prior studies have suggested that head injury might be a potential risk factor of amyotrophic lateral sclerosis (ALS). However, the association has not been well established. We aimed to provide a synopsis of the current understanding of head injury's role in ALS.

METHODS

We performed a systematic search in PubMed for observational studies that quantitatively investigated the association between head injury and ALS risk published before April 10, 2020. We used a random-effects model to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Fourteen eligible articles including 10,703 cases and 2,159,324 controls were selected in current meta-analysis. We found that head injury was associated with an increased risk of ALS (OR = 1.38, 95% CI: 1.20-1.60) and the association was slightly stronger concerning severe head injury and ALS risk (OR = 1.69, 95% CI: 1.27-2.23). Considering the number of head injuries (N) and ALS risk, the association was weak (OR = 1.23, 95% CI: 1.10-1.37, N = 1; OR = 1.29, 95% CI: 0.89-1.86, N ≥ 2). In addition, a strong association with ALS risk was found in individuals who suffered head injury <1 year (OR = 4.05, 95% CI: 2.79-5.89), and when the time lag was set at 1-5, 5-10, and >10 years, the pooled OR was 1.13, 1.35, and 1.10, respectively.

CONCLUSION

This meta-analysis indicates that head injury, especially severe head injury, could increase ALS risk. Although a strong association is found between head injury <1 year and ALS risk in the current study, this result suggests a possibility of reverse causation.

Examining the Relationship between Concussion and Neurodegenerative Disorders: A Review on Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD)

Background Current epidemiological studies have examined the associations between moderate and severe traumatic brain injury (TBI) and their risks of developing neurodegenerative diseases. Concussion, also known as mild TBI (mTBI), is however quite distinct from moderate or severe TBIs. Only few studies in this burgeoning area have examined concussion—especially repetitive episodes—and neurodegenerative diseases. Thus, no definite relationship has been established between them.

Objectives This review will discuss the available literatures linking concussion and amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD).

Materials and Methods Given the complexity of this subject, a realist review methodology was selected which includes clarifying the scope and developing a theoretical framework, developing a search strategy, selection and appraisal, data extraction, and synthesis. A detailed literature matrix was set out in order to get relevant and recent findings on this topic.

Results Presently, there is no objective clinical test for the diagnosis of concussion because the features are less obvious on physical examination. Absence of an objective test in diagnosing concussion sometimes leads to skepticism when confirming the presence or absence of concussion. Intriguingly, several possible explanations have been proposed in the pathological mechanisms that lead to the development of some neurodegenerative disorders (such as ALS and AD) and concussion but the two major events are deposition of tau proteins (abnormal microtubule proteins) and neuroinflammation, which ranges from glutamate excitotoxicity pathways and inflammatory pathways (which leads to a rise in the metabolic demands of microglia cells and neurons), to mitochondrial function via the oxidative pathways.

Conclusion mTBI constitutes majority of brain injuries. However, studies have focused mostly on moderate-to-severe TBI as highlighted above with inconclusive and paucity of studies linking concussion and neurodegenerative disorders. Although, it is highly probable that repetitive concussion (mTBI) and subconcussive head injuries may be risk factors for ALS) and AD from this review. It will be imperative therefore to conduct more research with a focus on mTBI and its association with ALS and AD.

Trauma and amyotrophic lateral sclerosis: a systematic review and meta-analysis

Background: Trauma especially head trauma is considered a potential risk factor of amyotrophic lateral sclerosis (ALS), but their association has not been well established. We aimed to determine the association of prior trauma with ALS risk. Methods: This study was performed according to the Meta-Analysis of Observational Studies in Epidemiology guideline to assess related literatures, and a random-effects model was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Results: Twenty-nine eligible articles involving 18,390 cases and 6,519,391 controls were included in this meta-analysis. The results showed that trauma was associated with an increased risk of ALS (pooled OR = 1.51, 95% CI: 1.32-1.73). Besides, patients with trunk trauma, head trauma and lower limb trauma had an increased risk of ALS, whereas no evidence suggested that upper limb trauma and spine trauma could increase ALS risk. Considering the number of traumatic events, the association between trauma and ALS risk was significant for patients with repeated trauma events (pooled OR = 1.21, 95% CI: 1.07-1.38). The results showed that individuals with a history of trauma within 5 years were more likely to be diagnosed with ALS (pooled OR = 1.84, 95% CI: 1.56-2.17). Importantly, both old trauma and very old trauma were found to be associated with an increased risk of ALS (pooled OR = 1.24, 95% CI: 1.12-1.38; pooled OR = 1.28, 95% CI: 1.10-1.49; respectively). Conclusions: This meta-analysis indicated that trauma could increase ALS risk, which may be applied for the clinicians to tailor targeted treatment regimens and make prophylactic strategies for ALS in traumatic patients.

Risk factors for amyotrophic lateral sclerosis: A regional United States case-control study

Most amyotrophic lateral sclerosis (ALS) cases are considered sporadic, without a known genetic basis, and environmental exposures are thought to play a causal role. To learn more about sporadic ALS etiology, we recruited n = 188 ALS patients from northern New England and Ohio and matched controls 2:1 from the general population of the same regions. Questionnaires evaluated the association between a variety of lifestyle, behavioral (ie, hobbies and activities), and occupational factors and the risk of ALS, including the duration of time between exposure and ALS onset, and exposure frequency. Head trauma was associated with increased ALS risk (adjusted odds ratio [OR] 1.60 95% confidence interval [CI] 1.04‐2.45), with significantly greater effects for injuries occurring 10 or more years prior to symptom onset (P = .037). ALS risk was increased for those reporting severe electrical burns (adjusted OR 2.86, 95% CI 1.37‐6.03), with odds ratios highest for burns after age 30 (OR 3.14), and for burns 10 or more years prior to symptom onset (OR 3.09). Hobbies involving lead were the most strongly associated with ALS risk (adjusted OR 2.92, 95% CI 1.45‐5.91). Exposures to lead 20 or more years prior to diagnosis had larger effect sizes compared to those occurring more recently. Holding a job in mechanics, painting, or construction was associated with ALS. The identification of these specific environmental factors associated with ALS highlight the need for future prospective and laboratory studies to assess causality, biological mechanisms, and find prevention or treatment opportunities.

Increased ISGylation in Cases of TBI-Exposed ALS Veterans

Veterans who have served in the military are at a nearly 60% greater risk of being diagnosed with amyotrophic lateral sclerosis (ALS). Literature reports suggest that a history of traumatic brain injury (TBI) may be a risk factor for ALS in veterans. However, no diagnostic biomarkers are available for identifying ALS risk/development in TBI-exposed veterans. Here, using a Wes assay, we show that ISGylation, a conjugated form of interferon-stimulated gene 15 protein, is significantly elevated in the lumbar spinal cords (SC-Ls) of TBI-ALS compared with ALS veterans without a previous history of TBI (nonTBI-ALS). Although not as striking as in TBI-ALS veterans, ISGylation is also increased in nonTBI-ALS compared with normal veterans. Notably, no changes in ISGylation were seen in occipital lobe samples obtained from the same patients, suggesting that elevated ISGylation is distinct to ALS disease-specific SC-Ls. Moreover, we detected increased ISGylation in cerebral spinal fluid samples of TBI-ALS veterans. Other results using cultured lymphocyte cell lines show a similar trend of increased ISGylation in ALS patients from the general population. Together, these data suggest that ISGylation could serve as a diagnostic biomarker for TBI-ALS veterans, nonTBI-ALS veterans, and nonveterans affected by ALS.

Amyotrophic Lateral Sclerosis Among Veterans Deployed in Support of Post-9/11 U.S. Conflicts

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a recognized military service-connected condition. Prior prevalence studies of ALS among U.S. war Veterans were not able to address concerns related to neurodegenerative sequelae of traumatic brain injury (TBI) and disregarded risk heterogeneity from occupational categories within service branches.

MATERIALS AND METHODS

We identified the prevalence of definite and possible ALS and cumulative incidence of definite ALS among Post-9/11 U.S. Veterans deployed in support of Post-9/11 conflicts (mean age 36.3) who received care in the Veterans Health Administration during fiscal years 2002-2015. Using a case-control study design, we also evaluated the association of TBI and major military occupation groups with ALS adjusting for demographics and comorbidities.

RESULTS

The prevalence of ALS was 19.7 per 100,000 over 14 years. Both prevalence and cumulative incidence of definite ALS were significantly higher among Air Force personnel compared to other service branches and among tactical operation officers and health care workers compared to general and administrative officers. Neither TBI nor younger age (<45 years) was associated with ALS. Depression, cardiac disease, cerebrovascular disease, high blood pressure, and obstructive sleep apnea were clinical comorbidities significantly associated with ALS in this population of Veterans.

CONCLUSION

This study among a cohort of relatively young Veterans showed a high ALS prevalence, suggesting an early onset of ALS among deployed military service members. The higher prevalence among some military specific occupations highlights the need to determine which occupational exposures specific to these occupations (particularly, Air Force personnel, tactical operations officers, and health care workers) might be associated with early onset ALS.

Mortality Among Professional American-Style Football Players and Professional American Baseball Players

Importance

Studies of American-style football players have suggested lower overall mortality rates compared with general populations, but with possibly increased neurodegenerative mortality. However, comparisons with general populations can introduce bias. This study compared mortality between US National Football League (NFL) and US Major League Baseball (MLB) players, a more appropriate comparison group of professional athletes.

Objective

To compare all-cause and cause-specific mortality between NFL and MLB players.

Design, Setting, and Participants

In this retrospective cohort study, the setting was US mortality from January 1, 1979, through December 31, 2013. The dates of analysis were January 2016 to April 2019. Participants were 3419 NFL and 2708 MLB players with at least 5 playing seasons.

Exposures

Participation in the NFL compared with the MLB.

Main Outcomes and Measures

Vital status and causes of death from the National Death Index from 1979 through 2013 were obtained. Cox proportional hazards regression models using age as the timescale were used to calculate hazard ratios (HRs) and 95% CIs to examine all-cause and cause-specific mortality among NFL players compared with MLB players, adjusted for race and decade of birth.

Results

By the end of follow-up, there were 517 deaths (mean [SD] age, 59.6 [13.2] years) in the NFL cohort and 431 deaths (mean [SD] age, 66.7 [12.3] years) in the MLB cohort. Cardiovascular and neurodegenerative conditions, respectively, were noted as underlying or contributing causes in 498 and 39 deaths in the NFL and 225 and 16 deaths in the MLB. Compared with MLB players, NFL players had significantly elevated rates of all-cause (HR, 1.26; 95% CI, 1.10-1.44), cardiovascular disease (HR, 2.40; 95% CI, 2.03-2.84), and neurodegenerative disease (HR, 2.99; 95% CI, 1.64-5.45) mortality. Comparing hypothetical populations of 1000 NFL and 1000 MLB players followed up to age 75 years, there would be an excess 21 all-cause deaths among NFL players, as well as 77 and 11 more deaths with underlying or contributing causes that included cardiovascular and neurodegenerative conditions, respectively.

Conclusions and Relevance

This study found that NFL players had elevated all-cause, cardiovascular, and neurodegenerative mortality rates compared with MLB players, although the absolute number of excess neurodegenerative deaths was still small. Factors that vary across these sports (eg, body habitus and head trauma) as opposed to those common across sports (eg, physical activity) could underlie the differences.

How did Lou Gehrig get Lou Gehrig's disease? Mycobacterium avium subspecies paratuberculosis in manure, soil, dirt, dust and grass and amyotrophic lateral sclerosis (motor neurone disease) clusters in football, rugby and soccer players

There are several suspected infectious causes of amyotrophic lateral sclerosis (ALS) or motor neurone disease including HIV-1 and species of Brucella, Cyanobacteria and Schistosoma. The increased rates and clusters of ALS in amateur and professional outdoor sports players including rugby, football and soccer players suggest a microorganism present in the grass, dirt and dust they play on and in may be a causative factor. The probable zoonosis Mycobacterium avium subspecies paratuberculosis (MAP) is heavily excreted in an infected domestic ruminant's feces or manure and is extensively distributed throughout the soil in countries where MAP infection of domestic livestock is longstanding. Like other zoonotic pathogens, MAP can be transmitted to humans by inhalation of aerosolized pathogen-contaminated soil, by direct contact of pathogen-contaminated grass, dirt and dust with mucus membranes lining the nose or mouth or through abrasions and cuts in the skin. Outdoor sports players may develop ALS after multiple oral, nasal or subcutaneous doses of MAP present in the dirt, dust and grass of their playing fields.

Traumatic Brain Injury Results in Cellular, Structural and Functional Changes Resembling Motor Neuron Disease

Traumatic brain injury (TBI) has been suggested to increase the risk of amyotrophic lateral sclerosis (ALS). However, this link remains controversial and as such, here we performed experimental moderate TBI in rats and assessed for the presence of ALS-like pathological and functional abnormalities at both 1 and 12 weeks post-injury. Serial in-vivo magnetic resonance imaging (MRI) demonstrated that rats given a TBI had progressive atrophy of the motor cortices and degeneration of the corticospinal tracts compared with sham-injured rats. Immunofluorescence analyses revealed a progressive reduction in neurons, as well as increased phosphorylated transactive response DNA-binding protein 43 (TDP-43) and cytoplasmic TDP-43, in the motor cortex of rats given a TBI. Rats given a TBI also had fewer spinal cord motor neurons, increased expression of muscle atrophy markers, and altered muscle fiber contractile properties compared with sham-injured rats at 12 weeks, but not 1 week, post-injury. All of these changes occurred in the presence of persisting motor deficits. These findings resemble some of the pathological and functional abnormalities common in ALS and support the notion that TBI can result in a progressive neurodegenerative disease process pathologically bearing similarities to a motor neuron disease.

Reversible induction of TDP-43 granules in cortical neurons after traumatic injury

Traumatic brain injury (TBI) has been proposed as a risk factor for neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). To determine whether TBI might trigger or exacerbate ALS-relevant pathology, we delivered a mild stab-wound injury to the motor cortex of three different ALS mouse models expressing mutations in SOD1, TDP-43 or FUS and scrutinized the effects on the formation of phospho-TDP-43 (pTDP-43) cytoplasmic granules. Stab-injury induced the formation of cytoplasmic TDP-43 granules in wt animals, peaking at 3dpi; a much larger response was seen in mutant TDP-43 mice, whose response peaked at 7dpi. The pTDP-43 granules did not colocalize with the stress markers TIAR-1 and FUS but colocalized with FMRP (35%) and with p62 (65%), suggesting their involvement in transport granules and their clearance by autophagy. A similar, albeit smaller effect, was seen in mutant FUS mice. In the SOD1^G93A mouse model, neither increase in pTDP-43 granules nor in SOD1 aggregates were detected. In all cases, pTDP-43 granules were cleared and the number of pTDP-43-positive neurons returned to baseline by 40dpi. Neither injury-related neuronal loss nor motor performance or survival was significantly different in transgenic mice receiving injury vs sham mice. Thus, trauma can trigger ALS-related TDP-43 pathology, the extent of which is modulated by ALS-related mutations. However, the pathological findings prove reversible and do not affect disease progression and neuronal vulnerability.

What is the Relationship of Traumatic Brain Injury to Dementia?

There is a long history linking traumatic brain injury (TBI) with the development of dementia. Despite significant reservations, such as recall bias or concluding causality for TBI, a summary of recent research points to several conclusions on the TBI-dementia relationship. 1) Increasing severity of a single moderate-to-severe TBI increases the risk of subsequent Alzheimer's disease (AD), the most common type of dementia. 2) Repetitive, often subconcussive, mild TBIs increases the risk for chronic traumatic encephalopathy (CTE), a degenerative neuropathology. 3) TBI may be a risk factor for other neurodegenerative disorders that can be associated with dementia. 4) TBI appears to lower the age of onset of TBI-related neurocognitive syndromes, potentially adding "TBI cognitive-behavioral features". The literature further indicates several specific risk factors for TBI-associated dementia: 5) any blast or blunt physical force to the head as long as there is violent head displacement; 6) decreased cognitive and/or neuronal reserve and the related variable of older age at TBI; and 7) the presence of apolipoprotein E ɛ4 alleles, a genetic risk factor for AD. Finally, there are neuropathological features relating TBI with neurocognitive syndromes: 8) acute TBI results in amyloid pathology and other neurodegenerative proteinopathies; 9) CTE shares features with neurodegenerative dementias; and 10) TBI results in white matter tract and neural network disruptions. Although further research is needed, these ten findings suggest that dose-dependent effects of violent head displacement in vulnerable brains predispose to dementia; among several potential mechanisms is the propagation of abnormal proteins along damaged white matter networks.

Risk of hospitalization with neurodegenerative disease after moderate-to-severe traumatic brain injury in the working-age population: A retrospective cohort study using the Finnish national health registries

BACKGROUND

Previous epidemiological studies suggest that working-aged persons with a history of moderate-to-severe traumatic brain injury (TBI) may have an increased risk for developing neurodegenerative disease (NDD) while persons with a history of mild TBI do not. In this comprehensive nationwide study in Finland, we assessed the risk of NDD and history of moderate-to-severe TBI in the working-age population.

METHODS AND FINDINGS

We performed a population-based follow-up study using the Finnish Care Register for Health Care to identify all persons between the ages of 18 and 65 years hospitalized during 1987-2014 due to TBI who did not have a baseline NDD diagnosis. We compared the risk of hospitalization with NDD between persons hospitalized due to moderate-to-severe TBI (intracranial lesions) and persons hospitalized due to mild TBI (no intracranial lesions). Follow-up NDD diagnoses were recorded from 1 year following the TBI to the end of 2014. NDD diagnoses included dementia, Parkinson disease, and amyotrophic lateral sclerosis. We used a Cox proportional hazards model, adjusting for age, sex, education, and socioeconomic group, to assess the association between TBI and NDD. In total, 19,936 and 20,703 persons with a history of moderate-to-severe TBI and mild TBI, respectively, were included. The overall time at risk was 453,079 person-years (median 10 years per person). In total, 3.5% (N = 696) persons in the moderate-to-severe TBI group developed NDD compared to 1.6% (N = 326) in the mild TBI group. After adjusting for covariates, moderate-to-severe TBI was associated with an increased risk for NDD, with a hazard ratio (HR) of 1.8 (95% CI 1.6-2.1) compared to mild TBI. Of the NDD subtypes, only moderate-to-severe TBI was associated with an increased risk for dementia (HR 1.9, 95% CI 1.6-2.2). Yet, this large-scale epidemiological study does not prove that there is a causal relationship between moderate-to-severe TBI and NDD. Further, the Care Register for Health Care includes only hospitalized persons; thus, patients diagnosed with NDD in the outpatient setting may have been missed. Additional limitations include the potential for miscoding and unmeasured confounds.

CONCLUSIONS

In working-aged persons, a history of moderate-to-severe TBI is associated with an increased risk for future dementia but not for Parkinson disease or amyotrophic lateral sclerosis.

Occupational formaldehyde and amyotrophic lateral sclerosis

Prior studies have yielded inconsistent evidence regarding the association between formaldehyde exposure and amyotrophic lateral sclerosis (ALS). We conducted a population case-control study in the Danish National Registries on the relationship between occupationally-derived formaldehyde exposure and ALS. Occupational history was obtained from a comprehensive and prospectively recorded pension database of all paid work in Denmark since 1964, and was linked to a job-exposure matrix to derive individual exposure estimates. Each case was matched to 4 age- and sex-matched population controls alive on the date of the case diagnosis via risk set sampling, and odds ratios and confidence intervals (CI) were calculated via conditional logistic regression, adjusting for potential confounders. There were 3650 incident cases of ALS in the Danish National Patient Register from 1982 to 2009. Among controls, 25% were ever employed in jobs with a positive prevalence of formaldehyde exposure. Exposure to formaldehyde was associated with a 1.3-fold increased rate of ALS (95% CI 1.2-1.4). This study suggests that formaldehyde exposure, or employment in formaldehyde-exposed occupations, is related to the risk of ALS.

Prevalence of potential sports-associated risk factors in Swiss amyotrophic lateral sclerosis patients

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) has been reported to occur with increased incidence amongst physically active people. The role of extrinsic risk factors as physical activity, head trauma and drug/pesticide-exposure in the pathophysiology of ALS and especially in the context of practising sports remains controversial.

MATERIALS AND METHODS

We retrospectively studied exposure to extrinsic factors in 92 ALS patients in the presymptomatic stage. Metabolic equivalents (METs) were calculated and the association of physical activity, drug intake, head trauma and participation in specific sports (football [soccer], ice hockey) with age at symptom-onset was evaluated.

RESULTS

Ninety-five percent of patients considered themselves physically active before symptom-onset. Total MET-values varied broadly and there was no correlation between vigorous physical activity and age at symptom-onset. Mild traumatic brain injury (prevalence = 16.7%) was the most frequent diagnosis after head/neck injury. A history of ≥1 head/neck injuries was associated with a younger age at symptom-onset (61.8 ± 11.0 vs. 54.1 ± 13.0, p = .013). In former football and ice hockey players the rate of vigorous physical activities was increased (p < .05), whereas total MET-values, frequency of head injuries and analgesic intake were not different compared to other ALS patients.

CONCLUSIONS

History of head injuries was the only extrinsic risk factor associated with accelerated neurodegeneration in ALS. There was no evidence for extrinsic factors predisposing former football and ice hockey players to ALS. Our data therefore support the hypothesis that not increased physical activity per se, but other unknown environmental factors and/or genetic profile or lifestyle-promoting physical fitness increases ALS susceptibility.

Motoneuron Disease: Basic Science

ALS is a relentless neurodegenerative disease in which motor neurons are the susceptible neuronal population. Their death results in progressive paresis of voluntary and respiratory muscles. The unprecedented rate of discoveries over the last two decades have broadened our knowledge of genetic causes and helped delineate molecular pathways. Here we critically review ALS epidemiology, genetics, pathogenic mechanisms, available animal models, and iPS cell technologies with a focus on their translational therapeutic potential. Despite limited clinical success in treatments to date, the new discoveries detailed here offer new models for uncovering disease mechanisms as well as novel strategies for intervention.

Physical Trauma and Amyotrophic Lateral Sclerosis: A Population-Based Study Using Danish National Registries

Prior studies have suggested that physical trauma might be associated with the development of amyotrophic lateral sclerosis (ALS). We conducted a population-based, individually matched case-control study in Denmark to assess whether hospitalization for trauma is associated with a higher risk of developing ALS. There were 3,650 incident cases of ALS in the Danish National Patient Register from 1982 to 2009. We used risk-set sampling to match each case to 100 age- and sex-matched population controls alive on the date of the case's diagnosis. Odds ratios and 95% confidence intervals were calculated using a conditional logistic regression model. History of trauma diagnosis was also obtained from the Danish Patient Register. When traumas in the 5 years prior to the index date were excluded, there was a borderline association between any trauma and ALS (odds ratio (OR) = 1.09, 95% confidence interval (CI): 0.99, 1.19). A first trauma before age 55 years was associated with ALS (OR = 1.22, 95% CI: 1.08, 1.37), whereas first traumas at older ages were not (OR = 0.97, 95% CI: 0.85, 1.10). Our data suggest that physical trauma at earlier ages is associated with ALS risk. Age at first trauma could help explain discrepancies in results of past studies of trauma and ALS.

Epidemiology of amyotrophic lateral sclerosis: A review of literature

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of motor neurons, resulting in worsening weakness of voluntary muscles until death occurs from respiratory failure. The incidence of ALS in European populations is two to three people per year per 100,000 of the general population. In Europe, crude prevalences range from 1.1/100,000 population in Yugoslavia to 8.2/100,000 in the Faroe Islands. Major advances have been made in our understanding of the genetic causes of ALS, whereas the contribution of environmental factors has been more difficult to assess and large-scale studies have not yet revealed a replicable, definitive environmental risk factor. The only established risk factors to date are older age, male gender and a family history of ALS. Median survival time from onset to death is usually 3 years from the first appearance of symptoms. Older age and bulbar onset are consistently reported to have poorer outcomes. However, there are conflicting data regarding gender, diagnostic delay and El Escorial criteria. The rate of symptom progression has been revealed to be an independent prognostic factor. Psychosocial factors and impaired cognitive function are negatively related to ALS outcome, while nutritional status and respiratory function are also related to ALS prognosis. The effect of enteral nutrition on survival is still unclear, although noninvasive positive pressure ventilation (NIPPV) has been found to improve survival. These findings have relevant implications for the design of future trials.

Comparison of diagnoses of amyotrophic lateral sclerosis by use of death certificates and hospital discharge data in the Danish population

Because ALS is rare, large-scale studies are difficult. Hospital and death certificate data are valuable tools, but understanding of how well they capture cases is needed. We identified 3650 incident cases in the Danish National Patient Register (NPR) between 1982 and 2009, using ICD-8 (before 1994) or ICD-10 codes. Death certificates were obtained from the Danish Register of Causes of Death. We obtained medical records for 173 of the cases identified in the NPR and classified these according to the El Escorial criteria. We compared ALS identification from death certificates to hospital discharges, and both to medical records. Results showed that the sensitivity for use of death certificates was 84.2% (95% CI 82.9-85.5%) and was significantly higher for females, subjects younger than 77 years, and when coded with ICD-8. Using only the underlying cause of death resulted in significantly lower sensitivity. The estimated overall positive predictive value (PPV) was 82.0% (95% CI 80.0-83.8%). Sensitivity and PPV were similar compared with medical records. In conclusion, we found that use of hospital discharges and death certificates is highly reliable and, therefore, a valuable tool for ALS epidemiologic studies. The possible effects on findings of slight differences by age, gender, and ICD coding should be considered.

Head injury does not alter disease progression or neuropathologic outcomes in ALS

OBJECTIVES

To study the effects of head injury on disease progression and on neuropathologic outcomes in amyotrophic lateral sclerosis (ALS).

METHODS

Patients with ALS were surveyed to obtain head injury history, and medical records were reviewed. Linear regression was performed to determine if head injury was a predictor for mean monthly decline of Amyotrophic Lateral Sclerosis Functional Rating Scale-revised (ALSFRS-R), while controlling for confounders. Head injury history was obtained from family members of ALS autopsy cases. The frequency of tau proteinopathy, brain TDP-43 inclusions, and pathologic findings of Alzheimer disease (AD) were examined in ALS cases with head injury compared to cases without. Logistic regression was performed with each neuropathologic diagnosis as an outcome measure and head injury as a predictor variable.

RESULTS

No difference was seen in rate of decline of the ALSFRS-R between patients with head injury (n = 24) and without (n = 76), with mean monthly decline of -0.9 for both groups (p = 0.18). Of 47 ALS autopsy cases (n = 9 with head injury, n = 38 without), no significant differences were seen in the frequency of tau proteinopathy (11% with head injury; 24% without), TDP-43 in the brain (44% with head injury; 45% without), or AD pathology (33% with head injury; 26% without). Independent logistic regression models showed head injury was not a predictor of tau pathology (p = 0.42) or TDP-43 in the brain (p = 0.99).

CONCLUSIONS

Head injury was not associated with faster disease progression in ALS and did not result in a specific neuropathologic phenotype. The tau pathology described with chronic traumatic encephalopathy was found in ALS autopsy cases both with and without head injury.

Risk factors for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease. It is typically fatal within 2-5 years of symptom onset. The incidence of ALS is largely uniform across most parts of the world, but an increasing ALS incidence during the last decades has been suggested. Although recent genetic studies have substantially improved our understanding of the causes of ALS, especially familial ALS, an important role of non-genetic factors in ALS is recognized and needs further study. In this review, we briefly discuss several major genetic contributors to ALS identified to date, followed by a more focused discussion on the most commonly examined non-genetic risk factors for ALS. We first review factors related to lifestyle choices, including smoking, intake of antioxidants, physical fitness, body mass index, and physical exercise, followed by factors related to occupational and environmental exposures, including electromagnetic fields, metals, pesticides, β-methylamino-L-alanine, and viral infection. Potential links between ALS and other medical conditions, including head trauma, metabolic diseases, cancer, and inflammatory diseases, are also discussed. Finally, we outline several future directions aiming to more efficiently examine the role of non-genetic risk factors in ALS.

Vestibular deficits leading to disequilibrium and falls in ambulatory amyotrophic lateral sclerosis

OBJECTIVE

To assess vestibular deficits in response to disequilibrium in ambulatory individuals with amyotrophic lateral sclerosis (ambALS).

DESIGN

All participants completed standard protocols for the Sensory Organization Test (SOT) by computerized dynamic posturography.

SETTING

Multidisciplinary amyotrophic lateral sclerosis clinic at an academic medical center.

PARTICIPANTS

Study participants (N=34) consisted of ambALS (n=19) and healthy controls (HC) (n=15).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Equilibrium scores (ESs) obtained from averaged sway amplitude in condition 5 (ES5) and condition 6 (ES6) of the SOT.

RESULTS

In conditions of altered somatosensory information with vision absent or vision sway-referenced, the mean ± SD scores for ambALS (ES5=51.4±22.5; ES6=50.8±22.1) were lower than those for HC (ES5=65.4±11.7, P≤.03; ES6=58.9±12.5, P>.05). Seven ambALS (37%) experienced a total of 19 falls during the sway-referenced support test conditions. There were no falls in the HC.

CONCLUSIONS

Nearly 37% of ambALS with normal clinical balance testing have decreased ability to use the vestibular input and required increased reliance on visual input for postural orientation to sustain equilibrium. The mechanism of this alteration in sensory preference is not completely clear. Extrapyramidal involvement early in ALS may be indicated.