Multiple sclerosis and heat don’t always play well together. People living with MS can be extremely heat sensitive. For me, increased body heat caused by ambient temperature, exertion, or sickness can cause MS symptoms to temporarily flare in a pseudoexacerbation. Add high heat index and humidity and my body begins to malfunction. I may have trouble walking a straight line, often get cranky, and have difficulty thinking clearly, get fatigued, and sometimes feel like my brain is turning into a pile of scrambled eggs.
Heat sensitivity in MS patients
In a multinational Internet-based survey of 2,529 MS patients, 70 percent of participants reported that high temperatures worsened their MS. In another study involving 256 MS patients, 58 percent reported heat sensitivity. Analysis revealed that heat sensitivity involved more than fatigue. 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.
Uhthoff’s phenomenon and pseudoexacerbation are terms that describe this temporarily worsening of MS symptoms due to an increase in body temperature. Once your body temperature returns to normal, the symptoms generally subside. It is not a true relapse of your MS.
Problems regulating body temperature
Beyond heat sensitivity and Uthoff's phenomenon, MS patients may have difficulty regulating their body temperature due to impaired neural control of autonomic and endocrine functions. 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.
Hypothermia has been documented in small numbers of MS patients with core body 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. My ‘normal’ body temperature runs closer to 95° F, so a temperature registering 99° F is more similar to 101° F in a healthy individual.
To sweat or not to sweat
When we become overheated, our bodies try to help by sweating and increasing blood flow to the skin. People with MS might not sweat as much because of impaired nerves that control normal thermoregulatory responses. However, they may experience greater increases of blood flow to the skin as compensation for impaired sweating.
Personally, I find that I sweat much more easily since developing heat sensitivity. Even a small amount of exertion will cause a slick back and damp shirt. This reinforces that everybody’s experience will be unique.
Cold sensitivity and MS
Some people living with MS may be more sensitive to cold temperatures than heat. Their symptoms get worse when the mercury falls. If this is the case, it’s important to try to keep body temperature steady, without overheating. Wearing layers of clothing, scarves, and/or wrist warmers may help, particularly if you also have Raynaud’s phenomenon.
Raynaud’s phenomenon and MS
Raynaud’s phenomenon is a condition characterized by discoloration in fingers and/or toes after exposure to changes in temperature. The tissue discoloration — which can range from purple, blue, red, or white — is typically caused by an abnormal spasm of blood vessels that reduces blood supply to the fingers or toes. Raynaud’s is commonly associated with connective tissue diseases, such as rheumatoid arthritis or scleroderma. But in an unusual case study, Raynaud’s was determined to be the presenting symptom for a person without a connective tissue disorder who was diagnosed with multiple sclerosis six months later.