Controlled population‐based comparative study of USA and international adult [55‐74] neurological deaths 1989‐2014

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From neurological studies covering the later part of the 20th century, evidence is growing of increases in a range of neurological morbidity and mortality especially related to Alzheimer's and Amyotrophic Lateral Sclerosis (ALS), known as Motor Neurone Disease (MND) in Europe.1 The accumulation of evidence has continued to build in this century.5 The first international comparison of the changing neurological mortality was between 1979‐1981 and 1995‐1997 in twenty‐one developed countries found that the dementias were starting a decade earlier in a number of nations.5 This was followed‐up in a second international study taking the results to 2010. The latter analysis used the later baseline years of 1989‐91, which confirmed the earlier onset of neurological morbidity and that neurological deaths continued to increase in the majority of the countries reviewed.1 Rises in USA the over‐75s neurological deaths were considerable as the USA had significantly greater increases than fourteen of the other twenty nations, with threefold rises in American men and a fivefold increase in women in just 21 years.8 Furthermore, there is a new interest in neurological diseases in Latin America and Asia, with a rising incidence than previously, although the rates remain lower than those found in developed countries,2 suggesting this is increasingly a worldwide phenomenon.
The rises in neurological mortality have been questioned as an artefact, for example, due to improved diagnosis of ALS14 and the effect of changing demographics giving rise to the “Gompertzian hypothesis.” This states that the neurological increases are a consequence of people living longer and therefore developing age‐related diseases that they had not lived long enough to develop previously.15 However, the diagnostic issue has limited impact as it is mortality rates that are measured not separate diagnostic categories, and at this point, there is little evidence of diagnostic uncertainty as the primary cause of death is categorized as being due to a neurological condition.1 Moreover, the Gompertzian position appears to have ignored the marked changes between the sexes and in different countries.1 Crucially, the Gompertzian hypothesis does not account for the substantial rise in early onset dementia reported in many Western countries.12
To reduce a primarily Gompertzian explanation, this population‐based study focuses upon people aged 55‐74 years, below life expectancies in the developed world and utilizes the latest WHO data, updated December 2016 to take the analysis up to 2014.23 Consequently, studying the adults aged 55‐74 over a relatively short time means any Gompertzian influence will be minimal. However, to place the results on adults aged 55‐74 in a wider context, the over‐75s rates and matching population increases are also examined to explore any possible strengths of the Gompertzian influence.
Two control mortalities are juxtaposed against neurological death rates, Cancer Mortality and Circulatory Disease Deaths (CDD) because they are considered age related. It should be noted, however, that this analysis is not designed to postulate about possible aetiologies, but only to determine whether there continues to be substantial increases in neurological deaths over the past two decades and whether there are any significant differences in the US rates and the other nations.
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