Small-Fiber Neuropathy: A Patient Overview

Small-fiber neuropathy is a type of peripheral nerve damage that affects the thin nerve fibers responsible for pain, temperature, and automatic body functions. These fibers are not measured by standard nerve tests, which is why many patients with small-fiber neuropathy have normal nerve conduction study and EMG results despite real and debilitating symptoms. This page explains what small-fiber neuropathy is, what causes it, and how it is diagnosed.

The two-tier peripheral nervous system

The peripheral nervous system contains two broad categories of nerve fibers, distinguished by their size and the presence of an insulating myelin sheath. Large fibers are myelinated and conduct signals quickly — they carry information about vibration, position sense, light touch, and movement commands. Small fibers are either unmyelinated (C fibers) or thinly myelinated (A-delta fibers) and conduct signals more slowly. They carry information about pain, temperature, itch, and the autonomic signals that regulate sweating, blood vessel tone, gut motility, heart rate, and other automatic body functions. Devigili and colleagues described the full range of small-fiber functions and the clinical criteria for small-fiber neuropathy in a 2008 Brain paper (PMID 18524793).

Nerve conduction studies and electromyography — the standard electrodiagnostic tests for neuropathy — measure only the large-fiber pathways. The tests record how quickly electrical signals travel through rapidly conducting nerves, which by definition excludes the small fibers. When small fibers are damaged but large fibers remain intact, NCS/EMG results come back normal. England and colleagues, writing in a 2009 American Academy of Neurology practice parameter, confirmed that this is a known limitation of electrodiagnostic testing, not a failure of the equipment or the technologist (PMID 19056666).

How common is small-fiber neuropathy

A 2013 Dutch population-based study by Peters and colleagues estimated the minimum prevalence of small-fiber neuropathy at approximately 53 per 100,000 people, with an annual incidence of approximately 12 per 100,000 (PMID 23997150). The authors noted that these figures likely underestimate the true burden because many cases go undiagnosed. A subsequent study from Olmsted County, Minnesota, published by Johnson and colleagues in 2021, reported an incidence of about 13 per 100,000 person-years, with rising rates in more recent years (PMID 34663645).

Small-fiber neuropathy is increasingly recognized as the underlying cause in many patients previously labeled with "idiopathic peripheral neuropathy" — the term applied when standard testing fails to identify a cause for clear neuropathic symptoms. Terkelsen and colleagues reviewed the diagnostic challenge of small-fiber neuropathy in a 2017 Lancet Neurology paper, noting estimates that 30 to 50 percent of idiopathic peripheral neuropathy cases are actually unidentified small-fiber neuropathy (PMID 29029847).

What patients experience

The symptoms of small-fiber neuropathy reflect the functions of the affected fibers. Patients typically describe burning, tingling, stabbing, or electric-shock sensations, most often beginning in the feet. The pain may be constant or come in waves. Many patients report that symptoms worsen at night and interfere with sleep.

Allodynia — pain produced by stimuli that would not normally cause pain, such as bedsheets touching the feet — is a common feature. Some patients describe the sensation as walking on glass or pebbles. When autonomic fibers are involved, additional symptoms may include lightheadedness when standing, abnormal sweating, dry eyes and mouth, constipation, bladder symptoms, and palpitations.

Small-fiber neuropathy can follow two spatial patterns. The length-dependent pattern starts in the feet and progresses upward. The non-length-dependent pattern features symptoms in patches across the body — including the face, scalp, or trunk — without a clear stocking-glove distribution. Khan and Zhou described the non-length-dependent pattern in a 2012 Muscle & Nerve paper and noted it is more often associated with autoimmune causes (PMID 22190313).

A defining feature of the patient experience is the gap between symptom severity and normal standard test results. Patients often describe being told their nerve tests are normal, with the implicit suggestion that nothing is wrong, even as they experience daily symptoms that significantly impair function. Hoeijmakers and colleagues documented this experience in a 2012 Nature Reviews Neurology overview of small-fiber neuropathy diagnosis and management (PMID 22641108).

What causes small-fiber neuropathy

Many conditions can damage small nerve fibers. The most common identifiable cause is diabetes or prediabetes — elevated blood glucose levels that may produce small-fiber damage even before meeting the threshold for type 2 diabetes diagnosis. Singleton and colleagues found increased prevalence of impaired glucose tolerance in patients presenting with painful sensory neuropathy in a 2001 Diabetes Care study (PMID 11473085).

Autoimmune diseases are an important cause category. Sjögren's syndrome, sarcoidosis, systemic lupus erythematosus, celiac disease, and inflammatory neuropathies can all produce small-fiber damage. Sjögren's syndrome in particular is associated with non-length-dependent small-fiber neuropathy; Mori and colleagues described the spectrum of Sjögren's-associated neuropathy in a 2005 Brain paper (PMID 16049042). Specific testing (anti-SSA/SSB antibodies, and sometimes minor salivary gland biopsy) is warranted when the pattern is suggestive.

Vitamin and metabolic causes include B12 deficiency, B6 toxicity from excessive supplementation, copper deficiency, and thyroid dysfunction. Infections including HIV, hepatitis C, and herpes viruses can produce small-fiber damage. A growing body of literature documents small-fiber neuropathy as a feature of long COVID. Oaklander and colleagues published skin biopsy evidence of reduced intraepidermal nerve fiber density in long COVID patients with persistent neuropathic symptoms in a 2022 Neurology Neuroimmunology & Neuroinflammation paper (PMID 35232750).

Genetic causes are an increasingly recognized category. Faber and colleagues established in a 2012 Annals of Neurology paper that gain-of-function mutations in the Nav1.7 sodium channel gene (SCN9A) cause a recognizable form of inherited small-fiber neuropathy (PMID 21698661). Mutations in SCN10A and SCN11A, encoding Nav1.8 and Nav1.9, have since been identified in additional patients.

Even after a thorough workup, 30 to 50 percent of confirmed small-fiber neuropathy cases will have no identifiable cause and receive the label "idiopathic small-fiber neuropathy." This designation reflects current limits of medical knowledge, not a failed workup. Patients with idiopathic small-fiber neuropathy can still benefit from established management approaches, and ongoing research continues to identify new causes.

How small-fiber neuropathy is diagnosed

Standard NCS/EMG does not detect small-fiber damage, so the diagnostic approach combines clinical assessment with specialized testing. The European Federation of Neurological Societies and the Peripheral Nerve Society published joint diagnostic guidelines, summarized by Lauria and colleagues in a 2010 European Journal of Neurology paper (PMID 20642627).

The cornerstone of objective diagnosis is skin punch biopsy with measurement of intraepidermal nerve fiber density (IENFD). A 3-millimeter skin sample from the lower leg, ankle, or thigh is sent to a specialized laboratory that counts the small nerve fibers crossing into the upper skin layer. A count below the age-matched lower limit of normal is diagnostic. The procedure is performed under local anesthesia, takes a few minutes, and leaves minimal scarring.

Other specialized tests include the Quantitative Sudomotor Axon Reflex Test (QSART), which assesses small autonomic fibers controlling sweating; Quantitative Sensory Testing (QST) for temperature and pain thresholds; and corneal confocal microscopy, an emerging non-invasive technique that images small nerve fibers in the cornea. Autonomic function testing can document autonomic involvement.

Laboratory testing during the workup targets identifiable causes: hemoglobin A1c and oral glucose tolerance testing, vitamin B12 with methylmalonic acid, vitamin B6, thyroid-stimulating hormone, autoimmune serologies (ANA, anti-SSA, anti-SSB, anti-thyroid antibodies), serum protein electrophoresis, angiotensin-converting enzyme, tissue transglutaminase for celiac disease, HIV, and hepatitis C. Genetic testing for sodium channel mutations is available when clinical suspicion warrants.

For evidence-based information about treatment options for small-fiber neuropathy

A separate clinical guide on this site covers the treatment landscape for small-fiber neuropathy — including which causes are reversible, which medications have evidence for symptomatic management, and what specialty referrals make sense — and is reviewed by a board-certified physician on our Medical Advisory Board before publication.

⏳ Under review: A clinical guide covering treatment options for this condition is currently under physician review and will publish soon.

Frequently asked questions