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).