The number of people experiencing numbness, tingling and pain in their feet with no known cause has been increasing over the last two decades, according at a new study published in the October 27, 2021, online issue of Neurology®, the medical journal of the American Academy of Neurology. Called small fiber neuropathy, the condition has different symptoms than large fiber neuropathy, which can cause weakness and balance issues. But in many cases people have both types of neuropathy.
For the study, researchers looked at records for everyone diagnosed with small fiber neuropathy in Olmsted County, Minn., and the adjacent counties during a 20-year period. They then compared those 94 people with 282 people of similar age and sex who did not have neuropathy. Participants were followed for an average of six years.
The study found that the condition occurred in 13.3 per 100,000 people, with the rate increasing during the study.
"This increase could be due in part to greater awareness," said study author Christopher J. Klein, MD, of the Mayo Clinic in Rochester, Minn., and a Fellow of the American Academy of Neurology. "Another possibility is that increasing levels of overweight and obesity in our area could be a factor in the higher rates of small fiber neuropathy. Higher body mass index, or BMI, is a risk factor for diabetes and high triglycerides, which may also lead to neuropathy."
The people in the study with neuropathy had an average BMI of 30.4, compared to 28.5 for the people who did not have neuropathy. A BMI of 18.5 to 24.9 is considered healthy; 25.0 to 29.9 is considered overweight; and 30.0 and higher is considered obese.
About 50% of the people with neuropathy had diabetes, compared to 22% of those without neuropathy.
The people with neuropathy were also more likely to have insomnia, at 86% compared to 54% for those without neuropathy. They were also more likely to have heart attacks, at 46% compared to 27%.
"Based on these findings, people with small fiber neuropathy should be screened for heart problems and their blood glucose should be monitored for signs of diabetes," Klein said.
The people with neuropathy were also more likely to take opioids for pain.
For 67 of the people with neuropathy, no cause could be determined, called idiopathic neuropathy. For 14 people, the neuropathy was caused by diabetes. Other causes included Sjögren syndrome and lupus.
A total of 36% of the people developed large fiber neuropathy during the study, an average of five years after they developed the small fiber version.
"The good news is that most people with idiopathic neuropathy do not develop major impairments or disability, but they did have many other conditions and an increased risk of heart attack, so the development of treatments and prevention methods is crucial," Klein said.
The main limitation of the study was that researchers looked back in time at medical records. A study examining all people with symptoms of small fiber neuropathy and following them over time should be conducted to confirm these findings, Klein said.
The study was supported by the Mayo Clinic Foundation, Mayo Clinic Center or Individualized Medicine and Mayo Clinic Center of MS and Autoimmune Neurology.
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