Causes

Diabetes is by far the most common cause of small fiber neuropathy. High blood sugar levels over time can damage the small nerve fibers, especially in your feet and hands. This happens because excess sugar in your blood can harm the tiny blood vessels that feed your nerves.

Impaired glucose tolerance and components of metabolic syndrome are often associated with small fiber neuropathy. This means even pre-diabetes or insulin resistance can start damaging your nerves. Diabetes comes in several forms that can damage nerves, including type 1 and type 2 diabetes, pre-diabetes and insulin resistance, metabolic syndrome, and slower-developing autoimmune diabetes (LADA). Managing blood sugar can help protect nerves.

Diabetes comes in several forms that can damage nerves, including type 1 and type 2 diabetes, pre-diabetes and insulin resistance, metabolic syndrome, and slower-developing autoimmune diabetes (LADA). Managing blood sugar can help protect nerves.

Autoimmune diseases are associated with small fiber neuropathy, though the exact way they cause nerve damage isn't always clear. In autoimmune conditions, your immune system mistakenly attacks healthy parts of your body, including your nerves. These conditions can cause inflammation that damages the small nerve fibers or affects the blood vessels that supply them. Some autoimmune conditions are more likely to cause neuropathy than others.

Some infections can lead to small fiber neuropathy, either during the active infection or as a long-term effect after recovery. The infection may directly damage nerve fibers or trigger immune responses that affect the nerves.

COVID-19 (SARS-CoV-2) has emerged as a cause of small fiber neuropathy, particularly in people with long COVID. Studies show that some people develop neuropathy symptoms like burning pain, numbness, and tingling weeks to months after their initial COVID infection. Research suggests COVID can damage small nerve fibers and trigger immune responses that affect the nervous system. Since COVID is a recent disease, more research is needed to fully understand how common this complication is and what the long-term effects might be.

There have been rare reports of small fiber neuropathy after COVID-19 vaccination. These cases appear to be very uncommon and may involve immune responses to the vaccine. Because vaccines are newer than the disease itself, ongoing research continues to study any potential connections. If you developed nerve symptoms after vaccination, your doctor can help determine the cause and appropriate treatment. The benefits of vaccination in preventing severe COVID-19 remain clear for most people.

Several other medical conditions can lead to small fiber neuropathy. These conditions affect your nerves in different ways, but they all can result in similar symptoms of pain, burning, and numbness.

Some medications and toxic substances can damage small nerve fibers. The good news is that stopping the harmful substance often prevents more damage and sometimes allows nerves to heal. Don't stop taking any prescribed medications without talking to your doctor first. They can help you weigh the benefits and risks and may be able to switch you to a different medicine if needed.

Certain medicines and toxins can harm small nerves, such as some chemotherapy drugs, older HIV medications, certain antibiotics, some heart or seizure drugs, heavy alcohol use, heavy metals, and industrial chemicals. Stopping or switching the offending agent often helps.

Some people inherit genes that make them more likely to develop small fiber neuropathy. These genetic forms are less common than other causes, but they're important to recognize because they can affect family members. Genetic neuropathies often start earlier in life and may progress differently than other types. If you have family members with similar symptoms, tell your doctor as this information can help with diagnosis. Learn more about getting a SFN diagnosis.

Rare genetic causes include Fabry disease, hereditary sensory and autonomic neuropathies (HSAN), mutations in ion channel genes like SCN9A, familial amyloidosis, and other inherited metabolic conditions. Genetic testing may be recommended when family history suggests a hereditary cause.