Nerve damage may explain some cases of long Covid: US study

A small study of patients suffering from persistent symptoms long after a bout of Covid-19 found that nearly 60% had nerve damage possibly caused by a defective immune response, a finding that could point to new treatments, US researchers reported on Tuesday.

The study involved in-depth exams of 17 people with so-called long Covid, a condition that arises within three months of a Covid-19 infection and lasts at least two months.

"I think what's going on here is that the nerves that control things like our breathing, blood vessels and our digestion in some cases are damaged in these long Covid patients," said Dr Anne Louise Oaklander, a neurologist at Massachusetts General Hospital and a lead author on the study published in Neurology: Neuroimmunology & Neuroinflammation.

As many as 30% of people who have Covid-19 are believed to develop long Covid, a condition with symptoms ranging from fatigue, rapid heartbeat, shortness of breath, cognitive difficulties, chronic pain, sensory abnormalities and muscle weakness.

Oaklander and colleagues focused on patients with symptoms consistent with a type of nerve damage known as peripheral neuropathy. All but one had had mild cases of Covid-19, and none had nerve damage prior to their infections.

After ruling out other possible explanations for the patients' complaints, the researchers ran a series of tests to identify whether the nerves were involved.

"We looked with every single major objective diagnostic test," Oaklander said. The vast majority had small fiber neuropathy - damage to small nerve fibers that detect sensations and regulate involuntary bodily functions such as the cardiovascular system and breathing.

The findings are consistent with a July study by Dr Rayaz Malik of Weill Cornell Medicine Qatar that found an association between nerve fiber damage in the cornea and a diagnosis of long Covid. 

In the current study, 11 of the 17 patients were treated with either steroids or intravenous immunoglobulin (IVIG), a standard treatment for patients with small nerve fiber damage caused by an immune response. Some improved though none were cured.

While the results would only apply to long Covid patients with this type of nerve damage, it is possible that immunotherapy could be helpful, said Dr Avindra Nath, an expert in neuroimmunology at the National Institute of Neurological Disorders and Stroke and a study co-author.

"To me, it suggests that we need to do a proper prospective study of these kinds of patients" testing the drugs in a randomized trial, Nath said.