Autism is considered a disorder of the brain. But a new study suggests that the peripheral nervous system, the nerves that control our sense of touch, pain and other sensations, may play a role as well. The exploratory study is published in the October 14, 2020, online issue of Neurology®, the medical journal of the American Academy of Neurology.
"More than 70% of people with autism have differences in their sensory perception," said study author Sung-Tsang Hsieh, M.D., Ph.D., of National Taiwan University Hospital in Taipei and a Fellow of the American Academy of Neurology. "For some people, even a light touch can feel unbearable while others may not even notice a cut on their foot. If larger studies can confirm these results, it is possible that further insight into the peripheral nervous system could help us understand how this disorder develops and potentially light the way for treating these distressing sensory symptoms that most people with autism experience."
The study involved 32 men with autism with an average age of 27. They were compared to 27 men and women with an average age of 33 who did not have autism or any diseases that would affect their peripheral nerves.
The people with autism completed questionnaires on their sensory symptoms. All of the participants had tests of their sensory nerves, including skin biopsies to look for damage to the small fibers in their nerves. In another test, heat pulses were applied to the skin. Researchers looked at the electrical signals produced by the nerves to see how they respond to the heat.
On the skin biopsy test, 53% of the people with autism had reduced nerve fiber density, while all of the people in the control group had levels in the normal range. People who had reduced nerve fiber density also were more likely to report feeling pain from the heat stimulus at a higher temperature than the control group.
"This indicates that the nerves have degenerated, similar to what happens for people with the condition of peripheral neuropathy, where the threshold for feeling heat and other sensations is higher than for other people," Hsieh said.
The study also found that the response to touch in people with autism differed according to whether or not they had nerve fiber damage. People who had normal nerves were more likely to say they disliked being touched and were uncomfortable with some textures, while people with nerve fiber damage were more likely to say they preferred going barefoot and could be unaware that they had gotten scratched or bruised.
Beyond its small size, another limitation of the study is that all of the participants with autism were male so the results may not apply to everyone with autism.
Chien Y-L, Chao C-C, Wu S-W, et al. Small fiber pathology in autism and clinical implications. Neurology. Published online October 14, 2020:10.1212/WNL.0000000000010932. doi:10.1212/WNL.0000000000010932
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