Neuro-Ophthalmology & Neuro-Otology
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May. 14, 2024
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03.15.2024
Globally, the number of people living with, or dying from,
neurologic conditions such as stroke, Alzheimer's disease and other
dementias, and meningitis has risen substantially over the past 30 years
due to the growth and aging of the global population as well as
increased exposure to environmental, metabolic, and lifestyle risk
factors. In 2021, 3.4 billion people experienced a nervous system
condition, according to a major new analysis from the Global Burden of
Disease, Injuries, and Risk Factors Study (GBD) 2021, published in The Lancet Neurology journal.
The analysis suggests that worldwide, the overall amount of disability,
illness, and premature death—a measurement known as disability-adjusted
life years (DALYs)—caused by neurologic conditions increased by 18%
over the past 31 years, rising from around 375 million years of healthy
life lost in 1990 to 443 million years in 2021.
The absolute number of DALYs is increasing in large part due to aging
and growing populations worldwide. However, if the impact of
demographics is removed through age standardization, rates of DALYs and
deaths [1] caused by neurologic conditions have declined by around a
third (27% and 34% respectively) worldwide since 1990—largely due to
better awareness, vaccination, and global prevention efforts for some
conditions such as tetanus (93% decrease in age-standardized rates of
DALYs), meningitis (62% decrease), and stroke (39% decrease).
The top 10 contributors to neurologic health loss in 2021 were stroke,
neonatal encephalopathy (brain injury), migraine, Alzheimer’s disease
and other dementias, diabetic neuropathy (nerve damage), meningitis,
epilepsy, neurologic complications from preterm birth, autism spectrum
disorder, and nervous system cancers. Neurologic consequences of
COVID-19 (cognitive impairment and Guillain-Barré syndrome) ranked 20th,
accounting for 2.48 million years of healthy life lost in 2021.
The most prevalent neurologic disorders in 2021 were tension-type
headaches (around 2 billion cases) and migraines (about 1.1 billion
cases). Diabetic neuropathy is the fastest-growing of all neurologic
conditions.
“The number of people with diabetic neuropathy has more than tripled
globally since 1990, rising to 206 million in 2021,” said co-senior
author Dr Liane Ong from the Institute for Health Metrics and Evaluation
(IHME), University of Washington, USA. “This is in line with the
increase in the global prevalence of diabetes.”
The current study builds on previous GBD analyses [2] to provide the
largest and most comprehensive analysis to compare the prevalence and
burden (illness and death) of nervous system disorders between countries
on a global scale between 1990 and 2021—expanding the number of studied
neurologic conditions from 15 to 37 that span from birth to later
life.
To better reflect that neurologic disorders can occur at any stage of
life, for the first time the GBD 2021 Nervous System Disorders
Collaborators studied neurodevelopmental disorders and neurologic
conditions in children, and found that they were responsible for almost a
fifth (18%) of all DALYs in 2021, accounting for 80 million years of
healthy life lost worldwide.
“Every country now has estimates of their neurologic burden based on
the best available evidence,” said lead author Dr Jaimie Steinmetz from
IHME. “As the world’s leading cause of overall disease burden, and with
case numbers rising 59% globally since 1990, nervous system conditions
must be addressed through effective, culturally acceptable, and
affordable prevention, treatment, rehabilitation, and long-term care
strategies.”
The study, conducted to inform ongoing advocacy and awareness efforts,
will support the WHO’s Intersectoral Global Action Plan on epilepsy and
other neurologic disorders 2022–2031 (IGAP) that aims to reduce the
impact and burden of neurologic disorders and improve the quality of
life of people with neurologic disorders as well as their caregivers
and families [3].
Over 80% of neurologic deaths and health loss occur in low- and middle-income countries (LMICs)
Overall, estimates reveal striking differences in nervous system burden
between world regions and national income levels. In high-income Asia
Pacific and Australasia – regions with the best neurologic health –
the rate of DALYs and deaths were under 3,000 and 65 per 100,000 people,
respectively in 2021. In these regions, stroke, migraine, dementia,
diabetic neuropathy, and autism spectrum disorders accounted for most
health loss.
In contrast, in the worst-off regions of western and central sub-Saharan
Africa, the rate of DALYs and deaths were up to five times higher (over
7,000 and 198 per 100,000 people respectively) in 2021, with stroke,
neonatal encephalopathy (brain injury), dementia, and meningitis the
biggest contributors to years of healthy life lost.
“Nervous system health loss disproportionately impacts many of the
poorest countries partly due to the higher prevalence of conditions
affecting neonates and children under 5, especially birth-related
complications and infections,” said Dr. Tarun Dua, Unit Head of WHO’s
Brain Health unit and one of the co-senior authors of the study.
“Improved infant survival has led to an increase in long-term
disability, while limited access to treatment and rehabilitation
services is contributing to the much higher proportion of deaths in
these countries.”
The authors highlight that, as of 2017, only a quarter of countries
globally had a separate budget for neurologic conditions, and only
around half had clinical guidelines. What’s more, the medical personnel
who care for people with neurologic conditions are unevenly
distributed around the world, with high-income countries having 70 times
more neurologic professionals per 100,000 individuals than LMICs.
Prevention needs to be a top priority
“Because many neurologic conditions lack cures, and access to medical
care is often limited, understanding modifiable risk factors and the
potentially avoidable neurologic condition burden is essential to help
curb this global health crisis,” said co-lead author Dr Katrin Seeher,
Mental Health Specialist at WHO’s Brain Health Unit.
The study quantified the proportion of nervous system burden that was
potentially preventable by eliminating known risk factors for stroke,
dementia, multiple sclerosis, Parkinson’s disease, encephalitis,
meningitis, and intellectual disability.
The analysis suggests that modifying 18 risk factors over a person’s
lifetime—most importantly high systolic blood pressure (57% of
DALYs)—could prevent 84% of global DALYs from stroke.
Additionally, estimates suggest that controlling lead exposure could
reduce the burden of intellectual disability by 63%, while reducing high
fasting plasma glucose to normal levels could reduce the burden of
dementia by around 15%.
“The worldwide neurologic burden is growing very fast and will put
even more pressure on health systems in the coming decades,” said
co-senior author Dr Valery Feigin, Director of Auckland University’s
National Institute for Stroke and Applied Neuroscience in New Zealand.
“Yet many current strategies for reducing neurologic conditions have
low effectiveness or are not sufficiently deployed, as is the case with
some of the fastest-growing but largely preventable conditions like
diabetic neuropathy and neonatal disorders. For many other conditions,
there is no cure, underscoring the importance of greater investment and
research into novel interventions and potentially modifiable risk
factors.”
“Nervous system conditions include infectious and vector-borne diseases
and injuries as well as non-communicable diseases and injuries,
demanding different strategies for prevention and treatment throughout
life,” said Steinmetz “We hope that our findings can help policymakers
more comprehensively understand the impact of neurologic conditions on
both adults and children to inform more targeted interventions in
individual countries, as well as guide ongoing awareness and advocacy
efforts around the world.”
Despite these important findings, the authors note several limitations,
including that, while they have done their best to capture all nervous
system health loss, some conditions were left out because they could not
isolate the neurologic component, including infections such as HIV,
which has a large impact in many parts of the world. And while the
study uses the best available evidence, estimates are constrained by the
quantity and quality of data, especially in LMICs.
Writing in a linked Comment, Professor Wolfgang Grisold, President of
the World Federation of Neurology, London, UK (who was not involved in
the study) says, “This important new GBD report highlights that the
burden of neurologic conditions is greater than previously thought. In
the next iteration, more attention should be given to neuromuscular
diseases, the effects of cancer in the nervous system, and neuropathic
pain. Comparing the disability caused by conditions with episodic
occurrence versus those that cause permanent and progressive disease
will remain challenging, because the effects on the individuals vary
substantially.”
For the full report, see the article published in Lancet Neurology.
Source: News Release
Lancet Neurology
March 14, 2024
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ISSN: 2831-9125