First-of-Kind Review Reveals Notable Climate Change-Related Impacts on Neurologic Health

Climate change and related airborne pollution are exacerbating many neurologic diseases in individuals around the world and posing challenges to the delivery of optimal neurologic care, according to a scoping review of the medical literature by Cleveland Clinic researchers published online in Neurology.

The review identifies neurologic conditions that have been shown to be impacted by various aspects of climate change — including stroke, hospitalization for dementia, and multiple sclerosis (MS) exacerbations — and highlights three top priorities for more detailed study:

• Determining strategies to mitigate neuroinfectious disease risk
• Elucidating the mechanisms of airborne pollutants’ pathophysiologic effects on the nervous system
• Identifying ways to improve neurologic care delivery in the face of climate-related disasters and instability

“Although international efforts are aiming to limit global temperature increases, irreversible ecological changes have already taken place and will continue as the planet warms,” says the paper’s corresponding author, Andrew Dhawan, MD, DPhil, a fellow in Cleveland Clinic’s Neurological Institute. “The impact of these changes on human health is becoming well documented, but their effects on risk of neurologic disease and on people with existing neurologic disease are less well defined. We conducted this review to better characterize these effects in the context of neurologic disease and identify the most pressing relevant research questions.”

The review at a glance

Dr. Dhawan and his Neurological Institute colleagues undertook their research as a scoping review — i.e., a preliminary assessment of the potential size and scope of available research literature. They searched the medical literature since 1990 for studies involving neurologic diseases as well as either climate change, temperature extremes or pollutants. They limited their search to human studies published in English and involving adults, not children.

Their review identified 364 relevant articles that they grouped into three broad categories:

• 38 studies relating to extreme weather events and temperature fluctuations
• 37 studies of emerging neuroinfectious diseases
• 289 studies of pollutant impacts

Among the key findings and observations:

• Extreme weather events and temperature fluctuations showed an association with stroke incidence and severity, migraine headaches, hospitalization among patients with dementia, and exacerbations of MS.
• Climate change extended the favorable conditions for emerging neuroinfectious diseases — including West Nile virus, meningococcal meningitis and tick-borne encephalitis — beyond their traditional geographic range, expanding the risks of these animal/insect-transmitted diseases to new human populations.
• Exposure to airborne pollutants — particularly nitrates and fine-particulate pollutants less than 2.5 microns in diameter — was linked to stroke incidence and severity, headaches, risk of dementia, MS exacerbations and, for some pollutants, Parkinson’s disease incidence.

Priorities for study and action

The authors recommend expedited study to develop understanding of emerging neurotropic infectious diseases. “Diseases such as Zika virus, West Nile virus and tick-borne encephalitis have both the potential and precedence for rapid spread across susceptible populations, with only a rudimentary understanding of their long-term effects on the nervous system,” they write, adding that better understanding of the connections with climate and human activity can guide strategies to mitigate risk.

They also call for expedited investigation of how airborne pollutants are mechanistically related to neurologic disease. “Our review indicates that specific aspects of air pollution, including particulate matter, are associated with heightened risk of stroke and neurodegenerative disease,” Dr. Dhawan observes. “This suggests a potential shared pathophysiology — perhaps small vessel disease — that should be explored.”

The authors likewise underscore a need to better enable neurologic care delivery in times of growing ecological instability, citing teleneurology as a promising means of ensuring care access when the effects of extreme weather physically isolate patients from care providers and facilities.

Worst effects may remain uncaptured

The authors note that their review may not adequately reflect the full impact of climate-related effects on neurologic disease because of several limitations, including its restriction to studies in English and a bias toward high-income countries due to overrepresentation of wealthier countries in the medical literature. “Because climate change disproportionally affects developing nations, the effects on neurologic health may be more severe than what we have found in this review,” Dr. Dhawan notes.

The review concludes by comparing the changing climate and pollutants to social determinants of health as mediators of disease burden. The authors write: “The elderly patient with dysautonomia or MS and lacking access to air conditioning, the patient with a small-vessel stroke in a city with increasing air pollution, or the patient with tick-borne encephalitis due to a vector not previously seen in their region are all vignettes that will undoubtedly become more common.”

“As we witness the effects of a warming planet on human health, it is imperative that neurologists anticipate how neurologic disease may change,” Dr. Dhawan says. “Our goal is to inspire action among neurologists and other clinicians to bring true change to reduce the harmful effects of the climate crisis.”