Understanding Small Fiber Neuropathy Pain
A Common Feature of Mixed Neuropathy
Medically reviewed by Katrina Carter, DPT
Small fiber neuropathy is a specific diagnostic classification of neuropathy, which is nerve damage, disease, or dysfunction. It can result in pain, loss of sensation, and digestive and urinary symptoms.
The most common causes of neuropathy include long-term diabetes, chemotherapy, alcohol use, and nutritional deficiencies. However, there are numerous types and causes of neuropathy. Small fiber neuropathy is diagnosed when it is clear that the small fibers of the nerves are involved. Extensive diagnostic testing is required to identify small fiber neuropathy.
Most of the time, neuropathy (such as peripheral neuropathy) involves small fibers and large fibers. Isolated small fiber neuropathy is rare, but experts are learning more about this type of nerve damage and how it can be treated.
This article describes the symptoms, causes, and potential treatments of small fiber neuropathy.
How Small Fiber Neuropathy Feels
Small fiber neuropathy can cause pain, as well as loss of sensation. Small fiber neuropathy may also cause autonomic dysfunction because small nerve fibers help mediate digestion, blood pressure, and bladder control.
The pain symptoms can range from mild or moderate discomfort to severe distress and can occur at any time. As the condition worsens due to progressing nerve damage, the intensity of the pain can decrease, but the loss of normal sensation and the autonomic symptoms may worsen.
Symptoms include:
The pain of small fiber neuropathy can manifest as hypersensitivity to touch and pain sensations and can cause pain without any trigger.
The loss of sensation can make you unable to accurately detect sensations of touch, pain, and temperature in the affected areas—which can lead to injuries, frostbite, or burns.
Symptoms of autonomic dysfunction can vary and may include constipation, diarrhea, incontinence, or urinary retention (not being able to drain the bladder completely). This type of erratic or inconsistent dysregulation is one of the features of nerve damage.
While it’s not well established, it’s possible that small fiber neuropathy can be part of some disorders that are not typically considered to be neuropathy. For example, the authors of a research study suggested that neurogenic rosacea, considered a skin condition, may have some components of small fiber neuropathy.
Related: The Anatomy of the Autonomic Nervous System
What Are Small Nerve Fibers?
The small nerve fibers that are damaged due to small fiber neuropathy are involved in mediating the pain and temperature sensations. These fibers are typically located in the superficial parts of the body, such as near the skin’s surface.
Small nerve fibers are distributed throughout the body, such as areas at the tops of your fingers and toes, your trunk, and in the internal organs. There are several types of small nerve fibers; two noted in small fiber neuropathy are the A-delta and C-fibers.
Most nerves are myelinated, meaning a special type of fat insulation called myelin protects them and increases the speed of nerve impulses. Small nerve fibers may be thinly myelinated, making them more susceptible to damage at earlier disease stages than heavily myelinated large fibers.
What Is the Peripheral Nervous System?
The peripheral nervous system (PNS) includes the nerves that send signals to your skeletal muscles, your skin, and internal organs. These signals may be somatic (voluntary) or autonomic (not under your control), as follows:
The sensory peripheral nerves detect and deliver sensation from your body to your spine. The signals are eventually delivered to your brain, allowing you to become conscious of your body’s sensations.
The motor peripheral nerves send signals to your skeletal muscles so that you can move voluntarily. They also send signals to your internal organs, such as your stomach, intestines, and bladder, to power the movements of these organs.
Who Gets Small Fiber Neuropathy?
Most types of peripheral neuropathy cause damage to the small fibers of the peripheral nerves and the large peripheral nerve fibers. Because of this, most peripheral neuropathies are a mix of small fiber neuropathy and large fiber neuropathy.
Common risk factors for mixed nerve fiber neuropathy include:
Nutritional deficiencies
Autoimmune disorders (the immune system attacks the body's own tissues)
Medication toxicity
Isolated small fiber neuropathy is rare. Some conditions that are known to cause isolated, small fiber neuropathy are:
Sjögren syndrome: This autoimmune disorder causes dry eyes and mouth, joint pain, and dental problems. It can also cause damage to nerves throughout the body.
Fabry disease: This condition causes a buildup of certain fats (lipids) in the body, leading to neurological effects.
Amyloidosis: This rare disorder causes a buildup of proteins in the body. The proteins can damage tissue, such as the heart or nerves.
Lewy body disease: This neurological disorder causes dementia and impaired movement, and it can also lead to nerve damage.
Lupus: This autoimmune disease affects joints, skin, and sometimes nerve tissue.
Viral infection: These types of infections usually cause a cold or gastrointestinal (GI) upset and, less often, can also cause other effects, such as small fiber neuropathy.
These conditions have been noted to cause isolated small fiber neuropathy or to begin as small fiber neuropathy before progressing to involve large nerve fibers. They can also start as a mixed neuropathy, with small and large fiber involvement.
Sometimes neuropathy begins as small fiber neuropathy during the early stages. This is because the thinly myelinated nerve fibers can be more easily damaged because they are not well protected by myelin. The highly myelinated large nerve fibers might not become damaged until the myelin is severely affected by disease.
Learn More: The 4 Neuropathy Types and How to Treat Them
Is Small Fiber Neuropathy Reversible?
One of the challenges of living with neuropathy is that the condition is not usually reversible by the time it’s diagnosed. That’s because symptoms of peripheral neuropathy typically become noticeable only after substantial nerve damage has occurred.
So, while small fiber neuropathy isn’t reversible, it can be possible to slow or stop the progression of nerve damage.
Why Is It So Hard to Know If You Have Small Fiber Neuropathy?
Simple diagnostic procedures do not easily examine small nerve fibers. Neuropathy is diagnosed based on changes in reflexes, sensation, and motor strength.
Distinguishing small fiber neuropathy from large fiber neuropathy involves invasive tests, such as examining intraepidermal nerve fiber density (the number of nerve endings in the skin) with a nerve biopsy sample obtained with a minor surgical procedure.
Most of the time, this diagnostic investigation is not useful for making treatment decisions. So, you may get a neuropathy diagnosis without a specific classification of small fiber neuropathy.
Small Fiber Neuropathy Progression
If you have a medical condition that’s causing damage to your small nerve fibers, it’s expected that the damage will continue to worsen unless the underlying medical condition is treated.
Usually, damage to the small fibers progresses at a relatively moderate rate, leading to more symptoms within months or years. All the small fiber nerves that are affected by the underlying condition will usually progressively deteriorate, regardless of where they are located in the body.
As the condition worsens, symptoms also worsen due to diminished sensation and increasing pain in small nerve fibers throughout the body.
Certain medications can help alleviate damage to the peripheral nerves. If you are diagnosed and treated at an early stage, it is possible to stop the progression of your small fiber neuropathy, potentially even preventing involvement of the large fibers.
Goal of Small Fiber Neuropathy Treatment
The treatment of small fiber neuropathy is aimed at two overall goals, which are preventing the progression of the condition and managing symptoms.
Treatment directed toward preventing the progression of small fiber neuropathy requires controlling the underlying medical condition. The treatment options depend on the cause of the small fiber neuropathy.
Treatments that may prevent the progression of small fiber neuropathy include:
Blood sugar control if you have diabetes
Discontinuing alcohol use
Immune suppression, such as intravenous immunoglobulin (IVIG) for control of autoimmune diseases, such as Sjögren’s disease or lupus
Plasmapheresis (blood is drawn, the cells are returned, and the plasma is treated and returned or exchanged) for the treatment of autoimmune disease
Nutritional supplementation for the treatment of vitamin deficiencies
Learn More: What Is Peripheral Neuropathy?
Symptomatic Treatment
You can get treatment for the symptoms of small fiber neuropathy. These treatments will not reverse or cure the condition but can help you find temporary relief.
Examples of symptomatic treatment include:
Pain management such as topical or oral medications
Physical therapy and rehabilitation to help improve coordination, which can be impaired by loss of sensation
Medications that relieve GI symptoms
Practical measures, such as wearing socks to prevent foot injuries
Managing Small Fiber Neuropathy Discomfort
The discomfort and sensory loss of small fiber neuropathy can cause substantial distress in your daily life. Pain can be present at any time without any trigger.
Furthermore, diminished sensation can lead to problems like bleeding or infections that could go unnoticed due to a lack of appropriate pain sensation. Even diminished touch sensation can result in problems with movement when you don’t get appropriate sensory feedback regarding what your body is feeling.
Coping with these issues can be challenging, but some strategies can help.
Pain
You can use medication as your healthcare provider prescribes to help alleviate the pain. Additionally, you may get relief from topical creams or gels that you can obtain over the counter. Be sure to ask your healthcare provider or pharmacist for advice regarding pain treatments.
Sometimes a cold compress or a heating pad can relieve the pain associated with small fiber neuropathy.
Loss of Sensation
Depending on how your loss of sensation affects your life, you could consider different strategies to help avoid injuries. Wearing gloves to help prevent frostbite (if your temperature sensation is impaired) could be beneficial. Additionally, testing the temperature of the water before you get into a bath or shower can help you avoid burns.
Autonomic Symptoms
You might need to adjust your diet and the timing of your meals to avoid discomfort. You also may need to have quick access to a toilet in case you have urgency.
Specialists to See for Small Fiber Neuropathy
Your healthcare provider may be able to diagnose neuropathy or peripheral neuropathy, but a diagnosis of small fiber neuropathy is not common. Identifying small fiber neuropathy typically involves a complex medical evaluation process that may require testing with electromyography, nerve conduction studies, or a nerve biopsy.
Sometimes quantitative sensory testing can help measure the extent of sensory involvement. During the test, you would give feedback about the degree of sensation you feel in response to stimuli such as temperature, touch, or position.
Treatment and medical management of neuropathy, including small fiber neuropathy, usually involves the care of a neurologist. Your neurologist might prescribe medication to help alleviate pain symptoms. You may also have medical interventions such as immunotherapy if there is concern that an autoimmune process could be causing your small fiber neuropathy.
Additionally, you could benefit from the care of a physical medicine and rehabilitation (PMNR) physician or a physical therapist so that you can work on exercises to help strengthen your muscles.
You may be referred to a registered dietitian for nutritional counseling.
Summary
Small fiber neuropathy is a classification of neuropathy that involves small nerve fibers. These nerve fibers detect sensation, pain, and temperature and help regulate involuntary functions like digestion. Small fiber neuropathy is not specifically dangerous but is a sign of an underlying disease damaging the body’s nerves.
Isolated small fiber neuropathy is extremely rare, but small fiber neuropathy may begin before large fibers are damaged. It’s rare to distinguish whether a person has small fiber or large fiber neuropathy because the diagnostic tests are highly specialized and may require a surgical nerve biopsy.
Symptomatic therapies are used for comfort and coping with limited sensation. Treatments are also directed at reducing damage from the underlying condition contributing to nerve damage.
If you have been diagnosed with peripheral neuropathy, or specifically with small fiber neuropathy, it’s important that you work with your healthcare providers to maintain medical treatment of the underlying cause, avoid alcohol, and maintain proper nutrition. This might involve vitamin supplementation if you have a vitamin deficiency.
