A study published Tuesday could offer new clues about a potential cause of long Covid-19 symptoms — and possible avenues for treatment.
The small, 17-person study, led by researchers from Massachusetts General Hospital and the National Institutes of Health, examined the many symptoms behind long Covid and found they may, in part, be driven by long-term nerve damage.
Anne Louise Oaklander, associate professor of neurology at Harvard University, led the study, which lasted from 2020 to 2021. She cautioned, however, that these are "preliminary results" from a very small and "biased data set," since the patients her team studied were already believed to have a neurological condition by their doctors.
Nevertheless, the study's findings could get researchers a small step closer to understanding what causes long Covid, a term the World Health Organization said "refers collectively to the constellation of long-term symptoms that some people experience after they have had Covid-19."
Evaluations of the 17 patients studied found evidence of peripheral neuropathy in 59 percent of them, or 10 people. A neurological disorder, peripheral neuropathy is a general term for damage to the nerves that connect the brain to the outside world. Common symptoms include weakness, fatigue sensory changes and pain in the hands and feet.
“What we asked is, could some of what’s going on with long-haul Covid actually reflect an undiagnosed peripheral neuropathy?” Oaklander said. Her results, she continued, indicated that small-fiber neuropathy, meaning damage done to peripheral nerve fibers, was the most common form.
"That's really point one: We found a real objective medical problem in over half of these patients," she said, adding that there was no correlation between how severe or mild the Covid case was and the type of nerve damage.
Finding that possible link between many common long Covid symptoms — difficulty getting through normal activities, faintness, rapid heart rate, shortness of breath, cognitive difficulties, chronic pain, sensory abnormalities and muscle weakness — could be a small step toward finding treatment options.
Peripheral neuropathy fits firmly within an established medical framework as a diagnosis one can receive from a doctor and for which there are some treatment options. But long Covid is still mysterious, and the medical understanding of it continues to evolve. As of now, it can't be technically diagnosed.
Oaklander said she hopes the new study improves experts' picture of long Covid.
“To me the next question is, how common is this? Is this a big deal that is a complete breakthrough, or is this going to end up affecting 1 percent of patients?” she said. “I cannot give you one answer either way.”
Dr. Fernando Carnavali, who leads the Center for Post-Covid Care at Mount Sinai Hospital in New York City, said he sees the study as one small piece of the immense amount of research being done to find answers for long Covid patients.
He was concerned, however, that the study could give a false sense of hope. While there may be a neurological link for some of the people in the study, he said, it likely will not be a diagnosis that fits others. Many of the 100 long-haul Covid patients he has seen, Carnavali noted, had already visited two to three neurologists before they came to see him.
Considering many are "desperate" for an answer, he said, it's best to be careful about drawing any strong conclusions.
"We need to have more information before we feel confident sharing something like this with patients, just to be sure that we are not exerting them more than they can handle," he said. "We know that these people cannot really exert themselves, neither cognitively nor physically or emotionally, so you have got to be careful."
Oaklander also encouraged caution, noting that she and other researchers had only "proposed an association" between small-fiber neuropathy and Covid, which does not mean causality.
"Certainly that's what we think, but it's very hard to prove 100 percent," she said. "You'd have to do much more rigorous experiments, which is what we want to do."