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New Discovery Regarding Fatigue and Temperature in MS

MS, fatigue and temperature

For the first time, researchers have documented an association between fatigue and internal body temperature in people with the most common form of multiple sclerosis (MS). What does this information mean to the estimated 2.5 million people who have MS?

Many people who have MS are especially sensitive to hot weather, fever, hot baths, getting overheated when exercising, and exposure to the sun. Even a slight rise in the body’s core temperature, as little as one-quarter to one-half of a degree according to the National Multiple Sclerosis Society, can have a negative effect on nerves that have been damaged and stripped of their protective coating (myelin).

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Briefly, what happens is that nerve signals that travel on demyelinated nerves tend to jump from nerve to nerve because the protective coating is gone. When those demyelinated nerves are exposed to a rise in temperature, the jumping signals can get more frantic and the impulses can be blocked (called conduction blocks).

The result can be a worsening of symptoms, but fortunately the exacerbation can be reversed once the source of the heat is eliminated or removed. Heat does not cause additional nerve damage or more rapid progression of the disease.

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The new study evaluated whether a rise in resting body temperature was linked to fatigue in individuals with relapsing-remitting MS (RRMS). Participants included 50 patients with RRMS, 40 healthy controls, and 22 individuals with secondary progressive MS.

The investigators documented the body temperature of all the participants using an ear (aural) infrared thermometer, for which the normal temperature is 98.2 degrees F (36.75 degrees C). The RRMS patients completed measures of general fatigue, physical fatigue, and cognitive fatigue.

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  • Mean body temperature was higher in the RRMS patients (98.7 degrees F/37.04 degrees C) than in the controls (98.3 degrees F/36.83 degrees C) and those with secondary progressive MS (98.2 degrees F/36.75 degrees C).
  • The higher core body temperature in the RRMS patients was associated with worse physical fatigue and general fatigue but did not have an association with cognitive fatigue

Study of MS, heat and physical function
An earlier study looked at the effects of heat on physical functioning in individuals with MS. A total of 23 heat-sensitive MS patients and 19 healthy controls participated and were exposed to a dry sauna and evaluated before the sauna and then immediately, one hour, and one day after exposure.

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The individuals with MS had a significantly higher core body temperature than did the controls immediately after leaving the sauna. They also performed more poorly on activities such as walking, rising from a chair, and reaching right after leaving the heat.

Thus a rise in outside (ambient) temperature causes the core body temperature to increase more in MS patients than in healthy controls and it also worsens physical function. However, those negative effects were temporary.

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The authors of the new study believe their findings offer an explanation as to why trials using cooling garments and aspirin (to fight fever) provide relief from fatigue in MS patients. Hopefully the results of this study will lead to more research on cooling methods to reduce fatigue in patients with relapsing-remitting MS.

National Multiple Sclerosis Society
Romberg A et al. The effects of heat stress on physical functioning in persons with multiple sclerosis. Journal of the Neurological Sciences 2012 Aug 15; 319(1-2): 42-46

Sumowski JF, Leavitt VM. Body temperature is elevated and linked to fatigue in relapsing-remitting multiple sclerosis, even without heat exposure. Archives of Physical Medicine and Rehabilitation 2014 Feb 19

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