80 Percent of People With MS Have This in Common, Study Says

If this one thing worsens your symptoms, talk to your doctor about MS.

Like Parkinson's and other potentially progressive diseases, receiving a Multiple Sclerosis (MS) diagnosis can be a terrifying prospect. A disease of the brain and central nervous system, it disrupts communication between the brain and the body, causing problems with coordination, poor balance, fatigue, pain, and vision loss. Currently, more than 2.3 million people in the U.S. are living with MS. Though life expectancy has increased for those with MS and most patients do not become severely disabled, there is currently no cure, and it remains notoriously hard to diagnose. In the absence of a single diagnostic test, doctors must systematically rule out other conditions to reach an MS diagnosis.

Complicating this process is the fact that no two MS cases are quite alike. Some are progressive, some are not. Patients can experience severely disabling symptoms or next to none. However, there's one thing that up to 80 percent of MS patients have in common. Read on to find out which subtle sign look out for, and to learn why it's essential to know—whether you've been diagnosed or not.

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Up to 80 percent of MS patients experience heat sensitivity.

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According to a July study published in the journal Temperature, between 60 and 80 percent of patients with MS experience heat sensitivity. This is called the Uhthoff phenomenon—also known as the Uhthoff sign or Uhthoff syndrome—a condition in which even minor increases in core body temperature can temporarily worsen a patient's neurological and other symptoms. MS patients with Uhthoff syndrome may experience enhanced muscle weakness, visual impairment, cognitive problems, imbalance, or fatigue. In some people, an increase as minor as a quarter of a degree can have an effect, the researchers say.

There's no shortage of biological and environmental factors that can lead to an increase in body temperature. However, the researchers point to "perimenstrual period, exercise, fever, sun-tanning, hot shower, sauna, psychological stress, and even [a] hot meal" as common culprits.

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In a much smaller group of patients, cold temperatures worsen symptoms.

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While the vast majority of MS patients with temperature sensitivity are impacted by heat, 20 percent of patients find their neurological symptoms worsened by cold. According to Medical News Today, some additional symptoms tend to be featured in these cases. Those include muscle tremors, a tingling sensation in the body, and muscle stiffness or tightening.

Experts believe that cold temperatures can affect patients for two reasons. First, "cold affects the speed of messages traveling along nerves that the disease has already damaged." And second, MS lesions in the brain—in which myelin is stripped from the nerves—may impact cold sensitivity.

Recognizing the syndrome may help lead to diagnosis.

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The Uhthoff phenomenon was first discovered in the 1890 by Wilhelm Uhthoff, a German ophthalmologist who noticed that some MS patients experienced vision changes and amblyopia—colloquially known as a "lazy eye"—following exercise. Uhthoff initially associated these optic symptoms with the strain of the workout, rather than the increase in bodily temperature, but subsequent studies conducted in the 1950s have clarified that heat change is the root cause.

This is significant because for decades following this discovery, medical experts then used a "hot bath test" based on the syndrome as a diagnostic test for the condition. While no one test can definitively identify MS, heat-related symptom changes may still help lead to diagnosis as part of a broader evaluation. This may include an MRI, spinal tap, blood tests, a review of your medical history, and other tools at your doctor's disposal.

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Sometimes, Uhthoff syndrome is mistaken for an MS relapse.

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In patients who have already received an MS diagnosis, there are major benefits to knowing the signs of Uhthoff syndrome. Perhaps most importantly, you'll be better able to distinguish between temporary changes brought on by heat and a more serious MS relapse.

"An exacerbation of MS (also known as a relapse, attack or flare-up) is the occurrence of new symptoms or the worsening of old symptoms. It can be very mild, or severe enough to interfere with a person's ability to function," explains the National Multiple Sclerosis Society (NMSS).

If you're thinking that sounds similar to the Uhthoff phenomenon, you're not wrong. But as the NMSS points out, "to be a true exacerbation, the attack must last at least 24 hours and be separated from the previous attack by at least 30 days…in the absence of infection, or other cause." Conversely, Uhthoff syndrome is known to last under 24 hours, making the duration of the symptom changes a helpful clue into your condition.

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Lauren Gray
Lauren Gray is a New York-based writer, editor, and consultant. Read more
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