Studies show that about 2.4% of the population suffers from peripheral neuropathy, rising to about 8% in older patients. Clinicians have also recently discovered the condition in some patients who have had COVID-19. One study found that up to 56% of COVID-19 patients reported symptoms of peripheral neuropathy after infection. This article focuses on the correlation between the two, as follows:
What causes peripheral neuropathy?
Neuropathies can have a slew of causes. Trauma, inflammation, diabetes, infections (viral or bacterial), certain medications, inherited conditions, poor nutrition, and hormone imbalances can be responsible. All of these factors can lead to toxicity and inflammation of the nerve and its coating, which in turn contributes to the physical breakdown of the cell and its ability to function. But no clear cause is found in nearly a quarter of the patients with this type of neuropathy.
Clinicians use further sub-classifications to describe the extent of the disease and how it manifests. For example, mono-neuropathies involve just one nerve, while polyneuropathies include many nerves.
Additionally, it’s crucial to know exactly what is going wrong with the nerve:
1. If the neuropathy is “demyelinating,” this means that the nerve has lost part of its myelin coating, a physiological “accelerator” of nerve signals that helps nerves talk very quickly to one another and to muscles.
2. Damage to the cell body of the nerve can occur if it is compressed or cut off from metabolic necessities (including glucose, the molecule that our cells use for energy) due to impingement from, for example, an abnormal growth or tumor.
Axonal damage, which affects the long stem of the nerve cell that lets it “talk” to other nerves, can happen due to similar metabolic toxicities or trauma. This is what scientists currently think happens, in large part, in other non-COVID viral models of peripheral neuropathy, such as HIV, hepatitis C, etc.
Why would COVID-19 cause peripheral neuropathy?
Lindsay McAlpine, MD, a neurologist and founder of the Yale NeuroCOVID Clinic, has conducted research on what is now known clinically as peripheral neuropathy after COVID-19. She notes that there are two main categories of neuropathy following COVID-19 infection. One is the “acute illness mediated type,” in which patients find themselves with sudden, severe neuropathy, generally around the same time as their active illness. The second is small fiber neuropathy, which results from damage to the thinnest, unmyelinated nerves in our body and often begins with burning pain in the feet. It typically arises somewhat later—around two to 12 weeks post-illness.
Peripheral neuropathy in COVID-19 patients has been reported in both axonal and demyelinating forms, according to the medical literature. Researchers suspect that COVID-19 associated neuropathy could be driven by several causes. One might be immune system dysfunction, in which the body attacks itself instead of, or in addition to, attacking viral particles. Or COVID-19 may have hemodynamic effects that interfere with how blood flows through the body’s blood vessels, damaging the nerves and leading to “ischemia” due to restricted blood/nutrient flow, known as critical illness neuropathy.
How do clinicians diagnose peripheral neuropathy?
To diagnose peripheral neuropathy, your clinician will ask you questions about your symptoms—when did they start, for example, and how would you describe the pain? The questions that Dr. McAlpine asks her patients include: “Is the pain intermittent? Is it localized to a certain part of your body? Is it patchy? Does it radiate? Are you numb, itchy, and/or hypersensitive?” Hallmarks of peripheral neuropathies include not only pain, but also weakness and numbness. Your answers to these questions can help clinicians pinpoint the cause of your symptoms.
How is peripheral neuropathy treated?
Clinicians often rely on a mixed-methods approach, including physical therapy and rehabilitation. Dr. McAlpine stresses the importance of “optimizing the environment for nerve healing”—that is, controlling other diseases such as diabetes that could be worsening symptoms, while also treating symptoms that can interfere with a patient’s function and sleep with medications, such as gabapentin (Neurontin®), pregabalin (Lyrica®), and duloxetine (Cymbalta®), that treat nerve pain.
