The fatigue multiple sclerosis (MS) patients experience is very different from the type experienced by healthy people. According to the National Multiple Sclerosis Society, fatigue occurs in about 80 percent of MS patients and “can significantly interfere with a person's ability to function at home and work." Fatigue is often cause for early retirement.
“When I share my research on fatigue in MS with colleagues or friends,” Victoria M. Leavitt, Ph.D., a neuropsychologist and co-founder of the Manhattan Memory Center in New York City told Healthline, “they say they know what it’s like, but the truth is they don’t.”
MS fatigue usually occurs every day, with lack of energy peaking by mid-afternoon. Onset can be sudden and is aggravated by heat.
In her earlier work, Leavitt found that outdoor temperature has an impact on cognition in MS patients. The results of that study made the team question whether internal temperature might also play a role in the disease process.
In their new study, Leavitt along with James F. Sumowski, Ph.D., a senior research scientist in neuropsychology and neuroscience at the Kessler Foundation, found that patients with relapsing MS who complained of fatigue also had a low-grade fever.
They studied 50 patients with relapsing-remitting MS (RRMS), 40 healthy controls, and 22 patients with secondary-progressive MS (SPMS). They discovered that warmer body temperatures in patients with RRMS were linked to more extreme fatigue. The volunteers with SPMS did not have a fever. This is the first-ever demonstration that body temperature is elevated in those with RRMS, and that it directly impacts their level of fatigue.
In-Depth with the Research Team
Healthline asked Leavitt and Sumowski for more details about their findings.
What's Causing the Low-Grade Fever?
"We think it is a disease-related inflammatory processes," explained Sumowski, “We know that elevated body temperature is linked to inflammation when otherwise healthy people experience a fever, as well as in other diseases (i.e., temperature of the joints in people with rheumatoid arthritis, temperature of the brain in acute stroke patients).”
“Rather than chronic inflammation, however, we think that body temperature may fluctuate with day-to-day fluctuations in inflammation among RRMS patients, although this still needs to be investigated directly," he added. "Indeed, many RRMS patients report day-to-day fluctuations in fatigue.”
Why Not Secondary-Progressive MS?
“This is a great question,” said Leavitt, “and it relates to our hypothesis that body temperature is related to inflammation. We know that RRMS is associated with inflammatory processes, which can lead to [relapses]. In contrast, inflammatory processes are less pronounced in progressive forms of the disease.”
“Indeed, there is a shift away from inflammatory lesions and clinical exacerbations after persons convert from RRMS to secondary-progressive MS (SPMS)," she added. "It makes sense, therefore, that (if body temperature is related to inflammation) body temperature would be higher in RRMS relative to SPMS.”
Is Heat Slowing Down Brain Signals?
Just as electronic devices malfunction when they become overheated, a fever might interfere with signals from the brain to the rest of the body. But according to Leavitt, there is surprisingly little to document this.
“For us, it is unclear whether body temperature has a direct relationship on neural transmission, or whether, alternatively, inflammation slows neural transmission and elevates body temperature," she said. "This is an important question for future research.”
During their study, Leavitt and Sumowski made an unexpected observation: hospital grade oral thermometers were surprisingly inaccurate. “Once we switched to in-ear thermometers,” said Leavitt, “we got much more accurate results.”
They theorized that if measuring body temperature from within the ear is more accurate, and the point of contact is closer to the brain itself, perhaps the fever is emanating from the disease activity within the brain. Leavitt referred to a study published last year that found that people with RRMS who had an elevated brain temperature experienced a greater level of disability.
“We are interested in extending this work,” said Leavitt, “as we think that brain temperature may bring us even closer to the source of elevated temperature and help us to understand whether it is related to inflammatory processes, fatigue, and other clinical symptoms.”
If you have RRMS and suffer from daily fatigue, what can you do? Besides the obvious goal of keeping your body cool, Sumowski said people with MS might want to, “avoid situations that may cause additional inflammation, including smoking, obesity, and exposure to allergens.”