Small fiber neuropathy occurs as a result of damage to the small fibers of the peripheral nervous system. These small fibers detect pain, heat, and itching sensations in the skin. They also regulate the autonomic functions of the cardiovascular system and the gastrointestinal tract.
Damage to the peripheral nervous system that affects the small fibers can cause burning pain or tingling sensations that begin at the feet and progress up the legs to the rest of the body.
Small fiber neuropathy may sometimes be a sign of an underlying health condition, such as diabetes or an autoimmune disease.
Keep reading to learn more about the causes and symptoms of small fiber neuropathy, as well as how doctors diagnose and treat this condition.
Pain in the feet and hands is the most common early symptom of small fiber neuropathy. However, this condition can also reduce the body’s ability to feel pain in a concentrated area and sense temperature.
As the disease progresses, people may notice symptoms in their knees, legs, and arms.
Other symptoms of small fiber neuropathy include:
- a tingling or prickling sensation (paresthesia)
- hypersensitivity to touch and temperature changes
- numbness in the feet, legs, or lower stomach
- bladder control issues
- sexual dysfunction
- excessive or infrequent sweating
- skin discoloration
- dry eyes and mouth
- extremely low blood pressure that may cause fainting
- rapid or irregular heartbeat
Symptoms of small fiber neuropathy can range from mild to severe. In the early stages, people often experience mild symptoms that may go unnoticed. Over time, symptoms typically worsen and progress to other areas of the body.
People often develop small fiber neuropathy as a result of an underlying medical condition, such as diabetes. According to the National Institutes of Health (NIH), up to 50% of people who have prediabetes or diabetes also develop small fiber neuropathy.
The NIH also note that mutations in the SCN9A and SCN10A genes can cause small fiber neuropathy. These genes carry instructions for making sodium channels, which cells use to produce and transmit electrical signals.
Examples of medical conditions that can cause small fiber neuropathy include:
- metabolic and endocrine disorders
- celiac disease
- Sjogren’s syndrome
- primary systemic amyloidosis
- familial amyloidosis
- Fabry disease
Other causes include:
- vitamin B-12 deficiency
- alcohol use disorder
- exposure to chemotherapy
- physical injuries
- illicit or prescription drug use
A doctor may diagnose a person with idiopathic small fiber neuropathy if they do not identify an underlying cause. In a 2018 study of 921 people with small fiber neuropathy, researchers found that 53% of the study participants had no associated underlying condition.
Doctors use a wide range of medical tests when diagnosing small fiber neuropathy. They will begin the diagnostic process by reviewing a person’s medical history and performing a physical exam.
A doctor may ask questions about a person’s family medical history, as well as any current or previous medical conditions that may explain their symptoms.
Many medical professionals consider skin biopsies the “gold standard” test for diagnosing small fiber neuropathy. A skin biopsy is a minimally invasive procedure in which a doctor takes several small skin samples that they send to a laboratory for analysis.
A technician or pathologist will examine the skin samples under a microscope. A doctor may diagnose small fiber neuropathy if the skin samples have fewer small nerve fibers than healthy skin.
In some cases, a doctor may also perform a nerve conduction test, electromyography, or both. Although doctors cannot conclusively diagnose small fiber neuropathy with these tests, they can use them to rule out other peripheral neuropathies and muscle disorders.
If necessary, doctors can use laboratory tests to check a person’s blood or urine for signs of glucose intolerance, immune system dysfunction, vitamin deficiencies, and liver or kidney problems.
Treatment for small fiber neuropathy varies depending on the underlying cause. People may notice that their neuropathy symptoms improve or resolve entirely when they manage or receive treatment for the underlying medical condition.
For people who have diabetes or other metabolic disorders, this means managing blood glucose levels, maintaining a moderate body weight, and eating a healthful, balanced diet.
Exercising regularly and quitting smoking can help heal constricted blood vessels that supply vital nutrients to the nerves.
Doctors may prescribe immunosuppressive drugs to treat people who have autoimmune diseases. These medications suppress immune activity in the body and reduce inflammation.
Other treatment options can help reduce pain due to small fiber neuropathy. These can include:
- antiseizure medication
- lidocaine creams and patches
- narcotics or opioid-based pain medications
Small fiber neuropathy is a type of peripheral neuropathy that affects the small nerve fibers in the skin.
This condition usually causes an unpleasant tingling sensation or burning pain in the feet. However, people who have small fiber neuropathy may have reduced sensitivity to heat and certain types of pain.
Although the symptoms of small fiber neuropathy usually begin in the feet, they can also affect the legs, hands, arms, and torso.
People can develop small fiber neuropathy as a result of nerve damage from another underlying medical condition, such as diabetes, an autoimmune disease, or an injury.
Treatments depend on the underlying cause. In most cases, managing the underlying medical condition can relieve the symptoms of small fiber neuropathy.