Heatwaves can worsen abnormal excitability of the brain in people with epilepsy, finds a new small-scale patient study by clinical scientists at UCL.
The research, published in Brain Communications, used intracranial electroencephalography (icEEG) tests - where small electrodes are inserted into the substance of the brain to measure electrical impulses - to track the brain activity of nine patients being evaluated for surgical treatment of medication-resistant epilepsy at the National Hospital for Neurology and Neurosurgery, in the summer months (May-August) of 2015 - 2022.
Genomic testing showed that none of the participants had known genetic epilepsies that are already associated with worsening of seizures during heatwaves.
In London, a heatwave is defined as three or more consecutive days with daily maximum temperatures of more than 28 degrees Celsius.
The nine patients involved in the study were, by chance, having icEEG recordings taken during spontaneous heatwaves in London, allowing the researchers to directly examine their brain activity during periods of unusually hot weather.
The researchers then compared this data to icEEG recordings taken from the patients during non-heatwave periods - while ensuring that all other conditions (apart from temperature) remained the same.
For each participant, the team logged any abnormal electrical activity across four 10-minute segments within and outside of heatwaves. They also tracked all seizures.
They found that, overall, more seizures were recorded by the icEEG during heatwaves compared with the non-heatwave period. Meanwhile, three patients also had more abnormal electrical brain activity aside from seizures during heatwaves.
Our research shows that for some people with epilepsy - in particular those with the most severe epilepsies - higher ambient temperatures increase the likelihood of having seizures.
This is an important finding, providing some of the first evidence that for some people who already have epilepsy, higher temperatures seen during heatwaves can make their condition worse.
Such information is important for the care of individual people with epilepsy, and also for broader efforts to ensure people with epilepsy can be kept safe as the climate changes."
Sanjay Sisodiya, Senior Author, Professor, UCL Queen Square Institute of Neurology
The current study sample size is relatively small as icEEG is not commonly undertaken and a heatwave had to have happened, by chance, during the recording.
However, the team now hope to have a bigger prospective study, and data are currently being collected.
Professor Sisodiya said: "Despite the study's limited sample size, our findings remain valuable in the context of climate change. As global temperatures rise and extreme weather events become more frequent, understanding the effects of heatwaves on brain activity is crucial."
Professor Sisodiya recently led a review of 332 papers published across the world, that explored that scale of potential effects of climate change on neurological diseases*.
The researchers found that the effect of climate change on weather patterns and adverse weather events is likely to negatively affect the health of people with brain conditions, including stroke, migraine, Alzheimer's, meningitis, epilepsy and multiple sclerosis. The new research adds to this analysis.
The research was carried out in collaboration with researchers at UCLH and funded by the Epilepsy Society, The Amelia Roberts Fellowship, and a UCL Grand Challenges Climate Crisis Special Initiative award.
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