The implications of increasing heatwaves for people with neurological conditions
A new review paper, published in the Journal of the Neurological Sciences, explores what is known about the impact of heatwaves on people living with neurological conditions. It makes the connection with the expected increase in extreme weather as a result of climate breakdown.
Impact of heat
As the climate changes, heatwaves are becoming more frequent and longer lasting. The impact of hotter temperatures on human health and health systems is the subject of research in several fields. This new review provides a concise and interesting overview of the impact and implications for neurology.
The review describes several studies that have found periods of higher temperatures (heatwaves) result in increased numbers of hospital visits and inpatient stays.
For example, an analysis of a database of information on adults with multiple sclerosis (MS) in the US, from 2003 to 2017, found that warm weather (1.5 degrees Celsius above average) was associated with an increased risk of visits to an emergency department or admission to hospital.
A further study found that emergency admissions of people with Parkinson's disease in Madrid, Spain, rose by 11.5% and mortality by 23% for every degree rise in temperatures above 34 degrees Celsius, during heatwaves in 2008 and 2009. Another study found that the risk of dementia-related admissions in England increased by 4.5% for every degree above 17 degrees Celsius.
Not every study finds such direct associations, but there is clearly a pattern.
What causes these impacts?
In MS, heat sensitivity is a common cause of symptoms (sometimes called Uhthoff's phenomenon). Taking a hot bath or exercise can result in a worsening of symptoms such as fatigue or vision impairment. The mechanism behind this is not well understood, but appears to be related to disrupted signals in the nervous system.
There are other mechanisms which affect people with neurological conditions during heatwaves. Some conditions impact the body’s ability to regulate its temperature. Certain medications can also increase the risk of heat-related illness. Some conditions (synucleinopathies) including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy can cause an inability to sweat.
A further mechanism that is likely to be important is the impact of sleep disturbance. Studies have found that short heatwaves caused disturbed sleep, likely to impact on brain function. Recent research on the glymphatic system has shown that the brain clears waste during sleep. Disturbed sleep during a heatwave could also impact this process.
The authors of the review state that, “Focused research is needed to determine the effects of extreme external heat on brain blood flow and glymphatic clearance, and their relationship to neurological diseases. [...] We postulate that the glymphatic system may play an important role in thermoregulatory processes and, therefore, may be crucial for human adaptation to global warming and heatwaves.”
How can we mitigate the impacts of heat?
Public health messaging around heatwaves tends to focus on the general population or the very young and very old. People with neurological conditions may not be aware of an increased risk.
The authors of the review suggest that heat-acclimation techniques may be useful for some people, but may not be appropriate for people with neurological conditions, in particular those with MS. Keeping cool could involve cold drinks, cool showers, cooling garments or ice-packs, or air conditioning devices.
The authors conclude that research, education and communication are all extremely important in adapting to the impact of heat and heatwaves.
Reference
Reis J et al. Neurological patients confronting climate change: A potential role for the glymphatic system and sleep. Journal of the Neurological Sciences, 458: 122900, 2024. https://doi.org/10.1016/j.jns.2024.122900