What is Small Fiber Neuropathy?

Jul 29

Small fiber neuropathy is a condition involving damage to the small fibers of the peripheral nervous system. Small fibers relay sensations of pain, temperature, and itching from the skin to the central nervous system. They are also involved in the regulation of important autonomic functions of the cardiovascular system and the gastrointestinal tract.

Damage to the small fibers of a peripheral nerve can cause burning pain or tingling sensations. These usually originate in the feet and progress upwards through the legs, and may 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 prevalence of small fiber neuropathy is unknown. Research implies a prevalence of approximately 53 cases of SFN per 100,000 people, with the condition being more common in males than females (6).

What are the Causes of Small Fiber Neuropathy?

There are many causes of small fiber neuropathy, the most common being diabetes, metabolic syndrome, HIV, sarcoidosis, and other inflammatory diseases (1). There are also some hereditary risks for SFN, but these remain incompletely understood.

Small fiber neuropathy is commonly associated with autoimmune diseases, genetic variations that affect sodium channel function, diabetes mellitus, and vitamin B12 deficiencies. In more than one half of patients no specific cause of SFN can be identified (7).

What are the Symptoms of Small Fiber Neuropathy?

The most prevalent symptoms of SFN are neuropathic pain and autonomic complaints, leading to a significant reduction in quality of life (7).

The most commonly reported symptoms are the sensation of “pins and needles”, with prickling, electric shock-like pain, and burning sensations. The pain onset is often sudden and severe, and can present without warning or obvious provocative activity. Restless legs and muscle cramps are also quite common.

Patients with small fiber neuropathy tend to experience pain, numbness, and tingling sensations in their lower limbs. They often experience what is known as dissociated sensory loss, with impaired pinprick perception but relatively preserved vibration perception. Vibration is conducted through large nerve fibers, which are spared in small fiber neuropathy (8).

Small fiber neuropathy is associated with a number of general symptoms as well. These include fatigue, cognitive dysfunction, sleep disturbances, widespread musculoskeletal pain, headache and temporomandibular disorders. (10).

There are also autonomic symptoms commonly seen with SFN. These include poor regulation of heart rate, problems with temperature sensitivity, and irritable bowel syndrome (11).

How is Small Fiber Neuropathy Diagnosed?

Small fiber neuropathy diagnosis is made by first determining the clinical phenotype. If the presentation involves primarily sensory symptoms, the diagnosis is confirmed by skin biopsy and Quantitative Sensory Axon reflex testing. If autonomic findings are present, the diagnosis is established through Quantitative Sensory Axon Reflex Testing, Thermoregulatory Sweat Testing, Sympathetic Skin Response Testing, Pupillometry, cardiovagal testing, and bladder function testing (8). As most cases of SFN involve combined sensory and autonomic symptoms, several different neurodiagnostic tests are usually required to establish the diagnosis.

How Does Small Fiber Neuropathy Affect the Nervous System?

Small fiber neuropathy can affect either small sensory fibers, autonomic fibers or both. This can lead to changes in sensation, problems with autonomic nervous system regulation, or combined symptoms. This wide range of possible symptoms virtually guarantees a large impact on quality of life.

Peripheral nerves are composed of several different types of nerve fibers. These fibers are classified based on structure, diameter, and conduction speed. Large diameter fibers have the fastest conduction speed, and conduct sensations like touch, pressure, vibration, and joint position sense to the central nervous system.

Small fibers are thin and relatively slowly conducting. These are either Aδ fibers, which conduct “fast pain,” such as the sharp pain from stubbing your toe, or C fibers, which conduct “slow pain,” the throbbing pain that sets in after stubbing your toe. Small fibers also convey sensations about temperature and itch to the brain.

C fibers also make up the peripheral outputs of the autonomic nervous system, which controls automatic functions like sweating, control of heart rate, respiration, and digestion, as well as controlling bladder and sexual function.

In small fiber neuropathy, Aδ and C fibers degenerate. This leads to the wide range of physical and autonomic symptoms seen with SFN.

This loss of appropriate sensory input and autonomic control leads to changes in central nervous system function. This can manifest as central pain sensitization. Small fiber neuropathies have been shown to result in abnormal recruitment of areas of the brain involved in pain processing. Volume reductions have been shown in the anterior cingulate cortex, an important area involved in pain processing. Functional connectivity has been shown to be reduced between the ACC and areas of the limbic system involved in emotional processing of pain sensations, as well as areas involved in visuospatial processing (5).

There is a great deal of overlap with small fiber neuropathy and other disorders of central pain processing, including Fibromyalgia. Research shows that at least 40% of SFN patients also suffer from Fibromyalgia (12). This is also a disorder of central pain processing (13), in which normal sensory inputs like touch and pressure can be perceived as painful, and also gives rise to generalized body pain, fatigue, sleep disturbances, and cognitive difficulties (14). Many of the symptoms overlap with SFN, and may be caused by the same pathology.

Research on Fibromyalgia is creating an expanded view of this condition, beyond purely a disorder of central pain processing. An alternative hypothesis views fibromyalgia as a stress-related dysautonomia with neuropathic pain features (15). Dysautonomias are conditions that lead to dysregulation of the autonomic nervous system.

Peripheral nerves have an important relay near the spinal cord called the dorsal root ganglia. It appears that the dorsal root ganglia may be the key autonomic-pain short-circuit site, where crosstalk between sensory, autonomic and pain signals lead to inappropriate perception and control of these systems. The dorsal root ganglia appear to be the fibromyalgia neural hub where different stressors can be transformed in neuropathic pain (16).

How is Small Fiber Neuropathy Usually Treated?

The best way to reduce small fiber neuropathy symptoms is to treat the condition or disease that caused the SFN. For example, if diabetes caused the neuropathy, the diabetes needs to be addressed and managed. If the condition results from autoimmunity, this also needs to be addressed with immune modulating medication.

Once the underlying condition has been addressed, neuropathic pain is generally treated with medication. Gabapentin and Tramadol have been shown to significantly reduce pain scores in neuropathic pain cases (2).

How is the NeuroRescue Program Different?

Once the underlying condition has been addressed, the symptoms of neuropathy generally remain. While medications have been shown to be somewhat helpful for reducing pain, such therapies mask symptoms rather than directly treat the pathology. If possible, we always want to restore function rather than cover up symptoms. A number of emergent therapies have been shown to be helpful to restore function in SFN.

Peripheral nerve electrical stimulation can be very helpful in treating small fiber neuropathy. Multiple studies have demonstrated significant reduction in neuropathic pain from electrical stimulation to the legs, using a wide variety of electrical modalities (4).

In your NeuroRescue Program we will often employ one or more electrical stimulation modalities in the treatment of your diabetic neuropathy. Transcutaneous electrical nerve stimulation therapy has demonstrated significant improvement in pain with patients with diabetic neuropathy, including small fiber neuropathy (3). Another such modality involves somatosensory evoked potential stimulation, which uses repetitive polarizing electrical stimulus to activate peripheral nerves. We may also employ a device called the Rebuilder, which uses several simultaneous currents to stimulate the entire affected sensory field of a specific nerve. Electrical stimulation is safe, painless, and effective. There are different indications for various types of electrical therapy, with the modalities employed tailored to the specifics of your case.

We may employ additional therapies, such as laser photobiomodulation. Both low-level and high-intensity laser therapy has been shown to be effective in controlling pain from neuropathies (17, 18).

We may also employ other advanced therapies, such as transcranial magnetic stimulation to reduce neuropathic pain (19), or hyperbaric oxygen therapy to improve healing (20).

We may employ supplementation strategies to improve peripheral nerve regeneration. Substantial evidence exists for the use of antioxidants like alpha-lipoic acid, and flavinoids like luteolin and quercitin in the treatment of neuropathy (21).

And as the majority of our small fiber neuropathy patients tend to struggle with fibromyalgia, we work hard to get that under control as well. Research shows that low-level laser therapy has benefits in reducing the severity of pain, number of tender points, and fatigue (22). Transcranial magnetic stimulation has been shown to be as effective in pain reduction as with considerably fewer side effects compared to the FDA approved pharmaceuticals used to treat fibromyalgia (23). Hyperbaric oxygen therapy has been shown to help reduce pain, anxiety, and fatigue in fibromyalgia (24). Supplementing with Vitamin D and Coenzyme Q10 have been demonstrated to be effective in the reduction of pain, reducing inflammation, and normalizing brain activity (24,25).

Every nervous system is different, and so is every NeuroRescue Program. We do not take a cookie-cutter approach to complicated neurological conditions. Your protocol will be determined by the specifics of your neurodiagnostic findings and the unique factors of your case.

How Does the NeuroRescue Program Work?

We design your unique NeuroRescue Program to be among the most comprehensive diagnostic and therapeutic protocols available today. We create individual NeuroRescue Programs based on a comprehensive analysis of every relevant neurological system and pathway, using gold-standard, cutting edge neurodiagnostic technologies and examination procedures and state-of-the-art therapies.

We begin with your Discovery Day, wherein we perform a comprehensive history of not only your condition, but your life on a timeline. This allows us to dive deeply into your case and see all of the factors that led to where you are now. It helps us uncover hidden problems and associated conditions that may be making it difficult for you to move your recovery forward.

Our examination allows us to identify the areas and pathways of your brain that are involved in your small fiber neuropathy. In all of our cases of assumed peripheral neuropathy, we begin by making certain that there are no central nervous system factors contributing to your symptoms. We do this by precisely quantifying the function of your visual, vestibular, and proprioceptive systems through computerized analysis of your eye movements, your inner ear reflexes, and your balance in a host of different sensory conditions.

We employ technologies including Videooculography and Saccadometry to measure several classes of eye movements. We use Video Head Impulse Testing to measure the function of your inner ear, and Computerized Dynamic Posturography to assess your balance in different sensory conditions.

We use NeuroSensoryMotor Integration testing to evaluate hand-eye coordination and cognition, and Virtualis testing to assess dynamic eye tracking and perception of vertical in a virtual reality environment.

We combine all of this with a comprehensive physical and neurological examination of your sensory, motor, autonomic, and cognitive systems. We review any relevant laboratory testing, radiological imaging, and prior neurodiagnostic testing, and integrate that information with our findings.

We use this information to identify which parts of your nervous system are working properly, which systems are struggling, and the precise point at which your systems fatigue.

We can then design a NeuroRescue Program that is unique and specific to your brain, and yours alone. Your NeuroRescue Program works to rejuvenate and reintegrate the damaged neurons and pathways in your central and peripheral nervous systems. It works to improve energy, endurance, and functional capacity within your involved fragile systems.

We use our technologies and procedures to not only see what we need to address, but also when it is time to stop and let you rest. We address your impaired neurological function from multiple angles of therapy, and provide metabolic support to improve neurological recovery.

While we cannot bring back neurons that have been lost, your NeuroRescue Program allows us to take the pathways that remain and maximize their efficiency and endurance. And by focusing on the integration of systems, we can do more than just get pathways working better, we can get them working together again. This gives us our best opportunity to return you to living a healthy, vibrant, and fulfilling life.

Your Next Best Step:

Living with small fiber neuropathy can be challenging, but there is hope for symptom management and functional recovery. To see if the NeuroRescue Program is right for you, contact one of our patient care coordinators to schedule your Discovery Day.

And remember, it’s never too late to start getting better.