What causes in Heat Intolerance in MS?

The destruction of myelin, the protective sheath which surrounds and protects nerve fibres causes the formation of plaques on the nerves which slow nerve impulses. A build up of heat slows down nerve transmission causing symptoms to worsen.

Many people with MS experience a temporary worsening of their symptoms when the weather is very hot or humid or they’re running a fever, sunbathe, get overheated from exercise, or take very hot showers or baths.

These temporary changes can result from a very slight rise in core body temperature, even as little as one-quarter to one-half of a degree, because an elevated temperature further impairs the ability of a demyelinated nerve to conduct electrical impulses.

What are the symptoms of Heat Intolerance?

• Some people notice that their vision becomes blurred when they get overheated; this is known as Uhthoff's Symptom.
• Others report an increase in symptoms such as fatigue, general tremor, intention tremor, decrease in cognitive function and memory problems.

For many years, the ‘Hot Bath’ test was used to diagnose MS. A person suspected of having MS was immersed in a hot tub of water, and the appearance of neurological symptoms or worsening of symptoms was taken as evidence that the person had MS.

It must be emphasised heat coupled with increased humidity generally produces only temporary worsening of symptoms and does not cause more actual tissue damage. The symptoms are generally rapidly reversed when the source of increased is dealt with and it is most important to remember that heat does not cause an actual exacerbation.

How can Heat Intolerance be managed?

• By drinking lots of fluids, preferably water or diluted fruit juices because dehydration due to perspiring can make it worse.
• By sucking on ice cubes or ice lollipops can help.
• By trying to remain in air-conditioned surroundings as much as possible on hot and humid days.
• Some people find cooling down before activity, by having a cold bath or shower gives them more energy or stamina.
• Using cooling products such as a mister spray or cooling gel in wristbands or scarves is also extremely effective.

Personal Experiences of Heat Intolerance:

“I get so exhausted, sometimes it’s an effort to move and I found the best thing is to lie with a damp towel. Travelling was becoming a nightmare so a car with air conditioning has been bliss. Even with temperatures in the low 70s I feel like I can’t cool off and feel like I’m in a boiler. The house in the summer looks like an electrical store with fans and air cooler.”

“My feet swell up to cauliflower-like proportions. Under normal circumstances it's all to do with lymph drainage if you're immobile, or like me sitting around a lot. I’ve been told that a daily lymph drainage massage technique would help alleviate this.”

“I can climb into my bath for a shower, but after taking the shower I can’t lift my legs high enough to get out. I have to wait to cool off before I can get my legs to work properly once more. I decided to get a ‘walk in’ shower with a bench seat, and to use a hand shower. With a hand shower I can either avoid my neck area with the hot water or use it to shower my neck with cool water.”

“My feet and ankles swell up alarmingly in the heat. They look like a pair of hot water bottles on the end of my legs. They do go down eventually, but I get a shock every time I look at them. When I’m sat in the shade my husband sprays my feet with one of those garden sprayers that I use for the ironing. It does seem to help!”

© Multiple Sclerosis Resource Centre (MSRC)