Can heat affect signs and symptoms of multiple sclerosis (MS)?

Heat transiently worsens symptoms of multiple sclerosis (MS) and can also contribute to fatigue in MS patients.  Patients can overheat when dehydrated, exercising, outside on a hot summer day, at the beach, or in a warm bathtub to jacuzzi.  Once patients have "cooled off" the symptoms improve.  It is thus important for patients with MS to drink plenty of water and try to keep the body cool.  
Louis Rosner
Heat is one of the most common of the aggravating factors known today. But doctors and patients weren't always armed with this information. In the 1930s doctors actually thought that heat was beneficial to multiple sclerosis (MS) patients, and many prescribed a fever treatment with a heat box. Since doctors knew of the higher incidence of MS away from the equator, they used to advise patients in northern climates to move to warmer ones. This only led patients from the refrigerator into the fire. Today we know that elevating the body temperature just one degree Fahrenheit, either from outside heat or fever from an infection, can cause new signs to appear or old signs to reappear - temporarily. In fact, because practically no other neurological disease reacts this way, heat was once used as a way to diagnose MS. The "hot bath test" was used to check for changes in vision or for the appearance of the Babinski sign.

Often those with MS will figure out the effects of heat themselves, relating such incidents as, "I was sunbathing at the beach, and after about an hour of lying in the sand, my vision went out in my right eye just like it did last year. I went home, turned on the air conditioner, and two hours later I was back to normal." Or, "In the middle of taking a hot shower, my right leg gave way, just like three months ago. When I got out, I could only drag my leg. But one hour later it was back to normal."

What causes this kind of temporary dysfunction? The best explanation is that a set of nerve fibers has a spot of myelin damage from the past. Nerve conduction recovered, but the myelin never completely repaired itself. When the body is overheated, conduction is slowed, and the nerve impulse traveling down this set of fibers cannot jump the gap where the myelin is damaged. The part of the body supplied by that bundle of nerves stops functioning temporarily until the nerve tract cools off.

Multiple Sclerosis

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Multiple Sclerosis

Too often, multiple sclerosis is thought of only as "the crippler of young adults." But in fact, 75 percent of all people with MS will never need a wheelchair. In Multiple Sclerosis, Dr. Louis J....

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.