Currently, a topic of intense research is long COVID. One recurring symptom that has been identified in some long COVID patients is peripheral neuropathy – damage to nerves that causes numbness and weakness in affected areas of the body (not including the brain or spinal cord).1
A study from researchers at Massachusetts General Hospital and Harvard Medical School investigated the potential link between long COVID and, more specifically, small-fiber polyneuropathy (SFN).1
What is small-fiber polyneuropathy?
Small-fiber polyneuropathy (SFN) refers to a condition where the axons – main branch of the nerve cell – of small nerves are damaged.1 These nerves include sensory nerves and autonomic nerves.
The autonomic nervous system is responsible for unconscious neural behaviors, such as digestion.
59% of sampled long COVID patients tested positive for SFN
As defined by the World Health Organization, long covid is the onset of any COVID-related symptoms within 90 days of the first COVID symptom.1 These long COVID symptoms must last for more than two months.
The study, published in Neurology Neuroimmunology & Neuroinflammation, examined 17 patients who had been infected with SARS-CoV-2 and were experiencing neuropathy symptoms.1 Participants had COVID-19 sometime between February 21st 2020 and January 19th 2021. Researchers studied participants for an average of 1.4 years.
Participants had no known history of neuropathy prior to SARS-CoV-2 infection.
Neuropathy was detected using a skin biopsy of the lower leg and upper thigh, an electrodiagnostic test – to measure nerve activity – and an autonomic function test.1
Just over 62% of lower leg biopsies revealed SFN, while 17% of electrodiagnostic tests and 50% of autonomic function tests confirmed SFN.1
Sixteen participants had mild COVID, while 1 participant had severe COVID requiring hospitalization. Symptoms of SFN arose, on average, within one month of mild COVID-19 illness.1
There are treatments available
Treatments included the use of IV immunoglobulins and/or corticosteroids; both are considered immunotherapies – therapies that alter the immune system response.1
The success rate of these treatments did not show any specific trend.1 Therefore treatment needs to be specific to the individual case.1 However, enough evidence was collected to suggest that SARS-CoV-2 infection may cause immune dysregulation that could contribute to SFN.1
Larger studies are needed
The authors noted that small fibers, in particular, are especially vulnerable to damage because they tend to lack myelin – the protective coating or insulator surrounding nerve cell stems (axons).1 They also noted that small fiber axons regenerate relatively quickly so there is hope that time could help heal symptoms.1
Of course, a limitation of this study is the small sample number of 17. However, as mentioned in the journal, this study shows a plausible link between long COVID and SFN, which could warrant larger studies to further test this association.1
Oaklander, A.L. et al. (2022). Peripheral Neuropathy Evaluations of Patients With Prolonged Long COVID. Neurology Neuroimmunology & Neuroinflammation; 9(3). Doi: 10.1212/NXI.0000000000001146.
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