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Global warming can aggravate multiple sclerosis symptoms. Here’s what you can do. » Yale Climate Connections

Strange weather in Los Angeles in February 2023 may have led to a spike in symptoms for people with multiple sclerosis, and Dr. Barbara Geisser’s practice was flooded with calls.

“The weather has been a little bit weird. It’s been rainy, and got actually pretty hot, and then got cold,” said Geisser, a neurologist and multiple sclerosis specialist with the Pacific Neuroscience Institute. “I’ve been hearing from a lot of patients, you know: ‘My feet are numb and tingly. I’ve had it before but it’s worse this week, or my balance is a little worse this week, or I’m just feeling more fatigued this week,’” Geisser recalled.

What is multiple sclerosis?

Globally, millions of people have multiple sclerosis, often called MS. It’s a disease in which the body’s immune system mistakenly attacks the nervous system. The staggeringly wide variety of symptoms includes blurred vision and fatigue, double vision, muscle weakness, loss of bladder control, cognitive difficulties, and loss of sensation. Symptoms vary from one person to the next depending on where the body’s immune system attacks its nerve-signaling architecture.

Researchers have found that increased numbers of MS clinic visits and reports of MS symptoms are linked to days with hotter temperatures and large temperature fluctuations. Already, climate change has made heat waves more frequent and intense, putting more patients at risk of aggravated symptoms.

Most patients find that heat causes a flare-up. Anything that raises someone’s core temperature — fevers, hot baths, exercise, exposure to warm environments — can make it harder for electrical signals to travel along already damaged nerve segments, triggering an onslaught of sensory, cognitive, vision, or movement problems. The risk of weather-related flares will only intensify as the climate changes more.

“There are a number of ways that climate disruption threatens the health and welfare of neurologic patients with multiple sclerosis,” said Dr. Bruce Snyder, a clinical professor of neurology at the University of Minnesota medical school. “Many of these consequences relate both directly to greenhouse gas emissions [and] warming and to related issues, such as air and water pollution.”   

Snyder and other neurologists are working to warn their patients so that they know what to expect and how to protect themselves.

The good news, according to Geisser, is that although the heat makes it harder for electrical signals to travel through previously damaged nerve fibers, the heat itself does not cause more nerve damage.

And patients can take steps to alleviate the symptoms, such as watching the weather forecast, finding an air-conditioned place to escape the heat, staying hydrated, and using cooling devices if they need to be in the heat.

“When people have a flare-up of symptoms due to getting overheated, they actually call it a ‘pseudo-exacerbation’,” Geisser said. Though the symptoms are real and uncomfortable, they usually completely resolve when the person cools down, and patients will not show new nerve damage on scans. This is different from an MS exacerbation, where new areas of the central nervous system become inflamed and injured.

How MS causes damage

With MS as with many autoimmune conditions, experts do not fully understand the reason why the immune system begins to attack and interfere with the healthy function of the central nervous system, made up of the brain, optic nerves, and spinal cord.

They do know that once the process starts, damage can occur anywhere in the system. Most of the attack is directed at cells and structures that are responsible for insulating nerve cells, allowing them to transmit smooth and rapid signals between each other. With each attack, the insulating layer, or myelin sheath, becomes inflamed and is eventually destroyed, a process called demyelination. These damaged areas distort the flow of healthy nerve signaling, leading to a wide range of symptoms.

Though heat-caused symptom flare-ups do not lead to new demyelination, they can be disturbing and debilitating.

MS patients at risk during weather disasters

More exposure to heat and weather extremes are not the only climate risks that can affect MS patients.

Snyder explains that many MS patients may be frail or have disabilities after years of living with the condition. That can put MS patients at higher risk of mental and physical trauma in the lead-up and aftermath of extreme weather events, like wildfires or floods, when emergency services may be overwhelmed or unavailable. And transportation services and evacuations can be more challenging for frail or disabled MS patients.   

Snyder points out that extreme weather events are also likely to interrupt access to medical care, pharmacies, insurance information, and in-home care. These disruptions can be particularly challenging for MS patients who rely on routine infusion therapy to manage their symptoms.

Potential links between MS and air pollution

Growing evidence also suggests that breathing polluted air can harm the nervous system. Researchers are studying whether air pollutants like particulate matter, sulfur dioxide, and nitrogen dioxide — all produced by burning fossil fuels — could increase the risk of developing MS or lead to relapses. According to several studies, breathing air pollution may worsen MS. But the jury’s still out on whether long-term exposure leads to the development of MS in the first place.

Geisser said she is not aware of an established connection between air pollution and MS, but suggests that air pollution may cause inflammation in the body. “That’s one of the reasons smoking is like the single worst thing for MS. The generalized inflammation may sort of turn on your immune system,” Geisser says.

What MS patients can do during hot weather

Beyond turning the fossil fuel spigot off to limit ever-increasing climate instability and hotter temperatures, there are key things MS patients can do to protect themselves in a warming world.

  • Monitor weather reports. Climate change has made it more likely that unseasonably warm temperatures can hit at any time in any region. If you know high-temperature days are coming, you can plan ahead to avoid prolonged exposure to higher temperatures.
  • Stay cool. Geisser says that people with MS were once told not to exercise because some patients would exercise, get overheated, and end up with worsened MS symptoms. But neurologists now tell people that exercise is one of the best things they can do. Even on hot days, she suggests MS patients find a cool, air-conditioned place for physical activity. If you have to go out and be active in the heat, stay hydrated and consider using a cooling device to keep your temperature down.
  • Remember these words of reassurance: Once MS patients can get their temperature back down to normal, heat-related symptoms typically resolve. “Heat will make your symptoms worse. It will not make your MS worse,” Geisser said.
  • Connect with your doctors. For any change in symptoms or concerns about heat, it’s important to seek the advice of your MS health care team. They are best equipped to help you manage your symptoms and medication regimen.

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