Small Fiber Neuropathy
Small fiber neuropathy (SFN) is a condition in which the small nerve fibers of the peripheral nervous system become damaged. These small fibers carry sensations of pain, temperature and itch from the skin to the brain and spinal cord. They also help regulate important automatic functions of the heart, blood vessels and digestive tract.
Damage to these fibers can cause burning pain or tingling. Symptoms usually start in the feet and move up the legs, and they can sometimes involve nerves throughout the body.
Small fiber neuropathy is often a sign of another underlying problem, such as diabetes or an autoimmune disease.
How Common Is Small Fiber Neuropathy?
The exact number of people with SFN is unknown. Research suggests about 53 cases per 100,000 people, with the condition somewhat more common in men than in women (6).
What Causes Small Fiber Neuropathy?
SFN has many possible causes. The most common include diabetes, metabolic syndrome, HIV, sarcoidosis and other inflammatory diseases (1). It is also linked to autoimmune diseases, vitamin B12 deficiency, and genetic variations that affect how sodium channels in nerves work. Hereditary risks are still not fully understood. In more than half of patients, no specific cause can be found (7).
What Are the Symptoms of Small Fiber Neuropathy?
The most common symptoms of SFN are nerve pain and problems with automatic body functions, both of which can greatly reduce quality of life (7).
People often describe pins and needles, prickling, electric shock-like pain and burning. Pain can start suddenly and severely, sometimes without any obvious trigger. Restless legs and muscle cramps are also common.
Many people with SFN have pain, numbness and tingling in their legs and feet. They often lose the ability to feel a pinprick while still being able to feel vibration. This happens because vibration is carried by large nerve fibers, which SFN usually spares (8).
SFN is also linked to more general symptoms, including fatigue, trouble thinking clearly, sleep problems, widespread muscle and joint pain, headaches and jaw (TMJ) disorders (10). Autonomic symptoms are common as well, such as poor heart rate regulation, sensitivity to temperature and irritable bowel syndrome (11).
How Is Small Fiber Neuropathy Diagnosed?
Diagnosis starts by identifying which kinds of symptoms are present. When symptoms are mainly sensory, SFN is usually confirmed with a skin biopsy and quantitative sudomotor axon reflex testing (QSART). When autonomic symptoms are present, testing may include QSART, thermoregulatory sweat testing, sympathetic skin response testing, pupil testing, cardiovagal testing and bladder function testing (8). Because most people with SFN have both sensory and autonomic symptoms, several tests are often needed. These diagnostic tests are typically performed by a neurologist or other physician, and we’re happy to help coordinate that care.
How Does Small Fiber Neuropathy Affect the Nervous System?
SFN can affect the small sensory fibers, the autonomic fibers, or both. That can lead to changes in sensation, problems with automatic body functions, or a combination. Because the possible symptoms are so wide-ranging, SFN can have a large impact on quality of life.
Peripheral nerves contain different types of fibers, grouped by their structure, size and how fast they carry signals. Large fibers are the fastest and carry touch, pressure, vibration and joint position sense.
Small fibers are thin and carry signals more slowly. Aδ fibers carry “fast pain,” like the sharp pain of stubbing your toe. C fibers carry “slow pain,” the throbbing ache that follows. Small fibers also carry temperature and itch sensations to the brain.
C fibers also make up the outgoing nerves of the autonomic nervous system, which controls automatic functions like sweating, heart rate, breathing and digestion, as well as bladder and sexual function.
In SFN, Aδ and C fibers break down. This leads to the wide range of sensory and autonomic symptoms seen with the condition.
Losing normal sensory input and autonomic control can also change how the brain and spinal cord work. One example is central sensitization, in which the nervous system becomes more sensitive to pain. Studies of people with SFN have found changes in brain areas involved in pain processing, including reduced volume in the anterior cingulate cortex and weaker connections between it and areas involved in emotion and visual-spatial processing (5).
Small Fiber Neuropathy and Fibromyalgia
SFN overlaps a great deal with other disorders of pain processing, including fibromyalgia. Research shows that at least 40% of people with SFN also have fibromyalgia (12). Fibromyalgia is also considered a disorder of central pain processing (13). In it, normal sensations like touch and pressure can feel painful, and it often comes with widespread pain, fatigue, sleep problems and cognitive difficulties (14). The two conditions share many symptoms and may share some underlying causes.
Research is expanding how fibromyalgia is understood. One theory views it as a stress-related dysautonomia, a disorder of autonomic regulation, with features of nerve pain (15). Researchers have also proposed that the dorsal root ganglia, relay stations for nerves near the spinal cord, may be a key site where sensory, autonomic and pain signals interact abnormally (16).
How Is Small Fiber Neuropathy Usually Treated?
The most important step in managing SFN is treating the condition that caused it. For example, if diabetes caused the neuropathy, managing the diabetes is essential. If the cause is autoimmune, it may need to be treated with immune-modulating medication from a physician.
Once the underlying cause is being addressed, nerve pain is often treated with medication. Gabapentin and tramadol have been shown to significantly reduce pain scores in neuropathic pain (2).
How the NeuroRescue Program Can Help
Even after the underlying condition is addressed, symptoms of neuropathy often remain. Our NeuroRescue Program works alongside your medical care, including any medications you take, with a focus on improving function and helping you manage symptoms. Please don’t change any medication without talking with your prescriber.
Electrical stimulation. Several studies have found that electrical stimulation of the legs can reduce neuropathic pain, using a variety of types of stimulation (4). Transcutaneous electrical nerve stimulation (TENS) has shown improvement in pain for people with diabetic neuropathy, including small fiber neuropathy (3). Your program may include one or more forms of electrical stimulation, such as TENS; somatosensory stimulation, which uses repeated electrical pulses to activate peripheral nerves; or the Rebuilder, a device that uses several currents at once to stimulate the full sensory area of a nerve. All of these are applied through the skin, and we choose the type based on the details of your case.
Laser therapy. Studies suggest that both low-level and high-intensity laser therapy can help reduce neuropathy pain (17, 18).
Transcranial magnetic stimulation. TMS has been studied for reducing neuropathic pain (19). At our clinic, TMS is provided by our psychiatric mental health nurse practitioner, who will evaluate whether it’s appropriate for you.
Nutritional support. Some research supports antioxidants like alpha-lipoic acid for neuropathy symptoms, and earlier research has explored plant compounds like luteolin and quercetin (21). When appropriate, we may recommend supplements as part of your program.
Recovery between sessions. Some programs include mild hyperbaric therapy as a structured recovery option between more demanding therapy sessions.
Support for fibromyalgia. Because many people with SFN also have fibromyalgia, we address both when needed. Research suggests low-level laser therapy may help reduce pain severity, tender points and fatigue in fibromyalgia (22). TMS has also been studied as a way to reduce fibromyalgia pain (23). Some studies suggest vitamin D and coenzyme Q10 supplementation may help reduce pain and inflammation (24, 25).
Every nervous system is different, so every NeuroRescue Program is different too. Your plan is based on your test results and the specific factors of your case.
How the NeuroRescue Program Works
Your NeuroRescue Program begins with your Discovery Day. We start with a detailed history of your condition and your life on a timeline. This helps us understand the factors that may have contributed to where you are now, and identify related conditions that may be making it harder to move forward.
Because symptoms that look like peripheral neuropathy can sometimes involve the brain and spinal cord as well, we also evaluate your central nervous system. We measure how your visual, vestibular and balance systems are working through computerized analysis of your eye movements, inner ear reflexes and balance under different conditions.
Our testing includes videonystagmography and saccadometry to measure several types of eye movements, the video head impulse test to measure inner ear reflexes, and CAPS computerized posturography to assess your balance under different sensory conditions. We also use NeuroSensoryMotor Integration testing to evaluate hand-eye coordination and cognition, and Virtualis testing to assess dynamic eye tracking and your perception of vertical in a virtual reality environment.
We combine this with a thorough physical and neurological exam of your sensory, motor, autonomic and cognitive systems. We also review any relevant lab work, imaging and prior testing, and integrate it with our findings.
Together, this helps us understand which parts of your nervous system are working well, which are struggling, and how quickly they tire. We use that information to design your personal NeuroRescue Program, aimed at improving energy, endurance and function in the systems that need support. Our testing also helps us decide when to push and when to let you rest.
We can’t bring back nerve cells that have been lost. What we can do is work with the pathways that remain, helping them work more efficiently and work better together. Our goal is to help you manage your symptoms, improve your function and enjoy more of your life.
Your Next Step
Living with small fiber neuropathy can be challenging, but there is hope for managing symptoms and improving function. To find out if the NeuroRescue Program is right for you, contact one of our patient care coordinators to schedule your Discovery Day.
It’s never too late to take the next step.
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