Heat sensitivity is a popular topic in the summer months, especially when you have multiple sclerosis. It has been a popular topic on my mind as of late with temperatures reaching 103°F with heat index values between 110°F and 115°F.
What is heat index?
The heat index, or “apparent temperature,” is a measure of how hot is truly feels when relative humidity is added to the actual air temperature. The National Weather Service will issue a heat advisory when the heat index is expected to exceed 105° to 110°F (depending on local climate) for at least two consecutive days. We have been experiencing “stupid heat” on the East Coast.
My fiance loves the heat, whereas I am not a big fan. Probably even worse than sheer heat is the humidity. When it is humid my mind and body take a serious downturn. I begin to have trouble walking straight. Then I get cranky as I have trouble thinking straight. I end up a pathetic mess as my brain gets turned into scrambled eggs.
That’s stupid heat!!
Heat sensitivity in MS patients
In a multinational Internet-based survey of 2,529 MS patients, 70 percent reported that high temperatures worsened their MS (Simmons, 2004). In another study involving 256 MS patients, 58 percent reported heat sensitivity. Analysis revealed that heat sensitivity involved more than fatigue (Flensner, 2011). Heat sensitivity itself is a key symptom in MS patients that is highly correlated with disabling symptoms such as fatigue, pain, concentration difficulty and urination urgency.
Beyond the terms heat sensitivity or heat intolerance, Uthoff’s phenomenon can be used to describe the temporary worsening of MS symptoms due to an increase in a person’s body temperature. You may also hear the term “pseudoexacerbation” used to describe this temporary (transient) condition. Once your body temperature returns to normal, the symptoms generally will subside. It is not a true relapse of your MS.
Did you know that persons with MS may have a decreased ability to regulate body temperature?
Beyond heat sensitivity and Uthoff’s phenomenon, MS patients may have difficulty in regulating their body temperature due to impaired neural control of autonomic and endocrine functions (Davis, 2010). The part of the brain that senses core body temperature and regulates it to about 98.6°F, the preoptic anterior hypothalamus, can be affected by MS, allowing for atypical fluctuations in body temperature.
In fact, hypothermia has been documented in small numbers of MS patients (Davis, 2010) with core temperatures ranging from to 86°F to 95°F. This can be problematic for patients when serious infections may be masked due to the absence of a typical fever response. I know that my “normal” core body temperature is closer to 97°F than 98.6°F. If I’m registering 98.6°F or higher, then I have a fever (for me).
When we become overheated, sweating and increased blood flow to the skin are ways in which our bodies help to bring temps down. Studies have reported reduced sweating responses in MS patients (Cartlidge, 1972; Noronha, 1968; Vas, 1969). Recent research reveals that decreased sweating could be caused by a reduced amount of sweat produced by each sweat gland and by impairments in the nerves which control normal thermoregulatory responses (Davis, 2010). Interestingly, MS patients demonstrated greater increases of blood flow to the skin compared with healthy controls, perhaps as compensation for impaired sweating (Davis, 2010).
Personally, I have found that I sweat much more easily since developing heat sensitivity. Even a small amount of exertion will cause a slick back and damp shirt. But part of that could be due to hormonal changes associated with peri-menopause since I am “of that age.” Last weekend when tremendous storms knocked out our power for days, two battery-operated fans and a headlamp were my best friends. Thankfully our power came back on before I became completely “stupid heat” dumb.
Note that the effect of heat stress on cognitive function is reported to be mild and reversible (Hämäläinen, 2012). Last weekend, I found that as the temperature of the house crept towards 90°F upstairs, I had difficulty in maintaining clear thought and lacked the motivation to attempt much writing. Once we were able to cool the house (and have access to ice once again), I did much better overall.
It seems to be an extraordinarily hot summer this year. Take care of yourself and try to keep cool.
REFERENCES AND SOURCES FOR FURTHER READING:
Cartlidge NE. Autonomic function in multiple sclerosis. Brain 1972;95:661–664.
Davis SL, et al. Thermoregulation in multiple sclerosis. J Appl Physiol 2010;109:1531–1537. doi:10.1152/japplphysiol.00460.2010.
D'hooghe MB, Haentjens P, et al. Sunlight exposure and sun sensitivity associated with disability progression in multiple sclerosis. Mult Scler 2012;18: 451. doi:10.1177/1352458511423778
Flensner G, et al. Sensitivity to heat in MS patients: a factor strongly influencing symptomology - an explorative survey. BMC Neurology 2011;11:27.
Geisler M, et al. Cooling and Multiple Sclerosis: Cognitive and Sensory Effects. Neurorehabil Neural Repair 1996;10:17.
Grahn DA, Murray JvLS, Heller HC. Cooling via one hand improves physical performance in heat-sensitive individuals with Multiple Sclerosis: A preliminary study. BMC Neurology 2008;8:14. doi:10.1186/1471-2377-8-14
Hämäläinen P, et al. The effects of heat stress on cognition in persons with multiple sclerosis. Mult Scler 2012;18(4):489–497. doi:10.1177/1352458511422926
Kondraske B, Kondraske GV, et al. Neuroperformance Evaluation of Multiple Sclerosis Disease Progression in a Clinical Trial: Implications for Neurological Outcomes. Neurorehabil Neural Repair 1993;7:153. doi:10.1177/136140969300700310
Meier DS, Christodoulou C. MS and heat: The smoke and the fire. Neurology 2012;78:938–939.
Noronha MJ, Vas CJ, Aziz H. Autonomic dysfunction (sweating responses) in multiple sclerosis. J Neurol Neurosurg Psychiatry 1968;31:19–22.
Opara J, Szwejkowski W, Pidsudko Z. Has the description of the Uhthoff phenomenon complicated rehabilitation in multiple sclerosis? Medical Rehabilitation 2009;13(1):15-18.
Saari A, et al. Sweating impairment in patients with multiple sclerosis. Acta Neurol Scand 2009;120(5):358-363. DOI: 10.1111/j.1600-0404.2009.01164.x
Simmons RD, Ponsonby A-L, van der Mei I, Sheridan P. What affects your MS? Responses to an anonymous, Internet-based epidemiological survey. Mult Scler 2004;10:202-211.
Vas CJ. Sexual impotence and some autonomic disturbances in men with multiple sclerosis. Acta Neurol Scand 1969;45:166–182.