Many people with MS experience a temporary worsening of their symptoms when the weather is very hot or humid or they run a fever, sunbathe, get overheated from exercise, or take very hot showers or baths. For example, some people notice that their vision becomes blurred when they get overheated—a phenomenon known as Uhthoff's sign. These temporary changes can result from even a very slight elevation in core body temperature (one-quarter to one-half of a degree) because an elevated temperature further impairs the ability of a demyelinated nerve to conduct electrical impulses.
The ‘Hot Bath’ Test Used for Years to Diagnose MS
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 neurologic symptoms or their worsening was taken as evidence that the person had MS. So heat is a very effective method of bringing out or increasing the symptoms of multiple sclerosis.
Heat-Related Symptoms are Temporary
It is important to remember that heat generally produces only temporary worsening of symptoms and does not cause more disease activity (demyelination or damage to the nerves themselves). The symptoms are generally rapidly reversed when the source of increased temperature is removed. People with MS who are planning to move to a very warm climate should try to visit first; plans may have to be changed if the weather seriously worsens MS symptoms.
Multiple Sclerosis Relapse or Pseudoexacerbation? Part Two