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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Neurology · Small Fiber Neuropathy

Symptoms and Differential Diagnosis: Recognizing SFN vs. Fibromyalgia

At a Glance

Small fiber neuropathy (SFN) and fibromyalgia cause similar chronic pain but have different origins. SFN stems from physical nerve damage, while fibromyalgia is a brain processing issue. Up to 50% of fibromyalgia patients actually have SFN, which can be confirmed with a skin punch biopsy.

If you live with chronic pain, you may have been diagnosed with Fibromyalgia (FM), a condition characterized by widespread aching and fatigue. However, many patients with these symptoms actually have Small Fiber Neuropathy (SFN), or sometimes both. While they feel similar, they are caused by completely different problems in the body [1].

Understanding whether your pain starts in your “wiring” (peripheral nerves) or your “computer” (the brain) is essential for getting the right treatment [1].

The Core Difference: Peripheral vs. Central

The primary difference between these two conditions is where the problem originates:

  • SFN is a Peripheral Problem: It is caused by the actual physical loss or dysfunction of the smallest nerve endings in your skin and organs [2]. These nerves, called A-delta and C fibers, are physically damaged or withered away [3][1].
  • Fibromyalgia is a Central Problem: It is primarily a disorder of central sensitization [4]. This means the brain and spinal cord have become “hyper-tuned” to pain, amplifying normal signals into painful ones, even though the peripheral nerves themselves may look structurally normal [1].

Comparing Symptoms

While both conditions cause pain, the type and location of the symptoms can provide clues to your doctor.

Feature Small Fiber Neuropathy (SFN) Fibromyalgia (FM)
Pain Type Burning, stinging, “electric,” or prickling [1]. Dull aching, widespread soreness, and stiffness [1].
Pattern Commonly “length-dependent” (starting in toes/feet) but can also be “non-length-dependent” (patchy, widespread) in autoimmune cases [5][6]. Widespread; felt throughout the body, often above and below the waist [4].
Autonomic Issues Common: Dizziness when standing, sweating changes, and GI issues [7][8]. Less common, though some “automatic” symptoms can occur [4].
Other Symptoms Often limited to pain and autonomic issues [9]. Profound fatigue, “brain fog,” and sleep disturbances [1].

Can You Have Both?

Yes. It is common for these conditions to coexist or be confused with one another. Research has shown that up to 30% to 50% of patients initially diagnosed with fibromyalgia actually meet the medical criteria for SFN [10][11].

In some cases, the constant pain signals from damaged peripheral nerves (SFN) can eventually “exhaust” the brain, leading to the central hypersensitivity seen in fibromyalgia [12].

Why Misdiagnosis Happens

Misdiagnosis is frequent because both conditions often result in “normal” standard tests like EMGs or MRIs [5]. To tell them apart, doctors must use specialized tools:

  • Skin Punch Biopsy: This is the most reliable way to identify SFN. A doctor takes a tiny sample of skin and counts the Intraepidermal Nerve Fiber Density (IENFD) [13]. If the fiber count is low, it confirms SFN [14].
  • Autonomic Testing: Tests that measure your sweat response or heart rate changes can point toward SFN [13][9].
  • Clinical Criteria: Fibromyalgia is usually diagnosed using a “widespread pain index” and by ruling out other structural damage [4].

If your fibromyalgia treatments aren’t working, or if your pain feels like it is burning and concentrated in your feet, it may be time to ask your doctor about testing for small fiber damage [15][16].

Return to Overview

Common questions in this guide

Can small fiber neuropathy be misdiagnosed as fibromyalgia?
Yes, research shows that up to 30% to 50% of patients diagnosed with fibromyalgia actually have small fiber neuropathy. Because standard nerve tests like EMGs and MRIs often come back normal for both conditions, they are easily confused without specialized testing.
What is the main difference between SFN and fibromyalgia?
SFN is caused by physical damage to small peripheral nerve endings, often creating a burning, stinging, or electrical pain that starts in the feet. Fibromyalgia is a central nervous system issue where the brain amplifies pain signals, causing widespread aching, soreness, and stiffness.
What test can confirm if I have small fiber neuropathy?
A skin punch biopsy is the most reliable way to definitively identify SFN. Your doctor will take a tiny skin sample to check your Intraepidermal Nerve Fiber Density (IENFD), and a low nerve fiber count confirms small fiber damage.
Can I have both small fiber neuropathy and fibromyalgia at the same time?
Yes, it is common for these conditions to coexist. The constant pain signals from damaged peripheral nerves in SFN can sometimes overwhelm the brain, leading to the central hypersensitivity that characterizes fibromyalgia.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Could my chronic pain be caused by a loss of peripheral nerve fibers rather than a central processing issue like fibromyalgia?
  2. 2.Since I have symptoms like lightheadedness and digestive issues, could these be signs of small fiber autonomic dysfunction?
  3. 3.Does the pattern of my pain (starting in my feet versus being widespread) suggest one condition over the other?
  4. 4.If I have already been diagnosed with fibromyalgia, is it possible I have comorbid small fiber neuropathy that requires a skin biopsy to confirm?
  5. 5.Would a skin punch biopsy for Intraepidermal Nerve Fiber Density (IENFD) help differentiate my symptoms?

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Could Fibromyalgia Be Small Fiber Neuropathy Instead?

References

References (16)
  1. 1

    The challenge of differentiating fibromyalgia from small-fiber neuropathy in clinical practice.

    Bailly F

    Joint bone spine 2021; (88(6)):105232 doi:10.1016/j.jbspin.2021.105232.

    PMID: 34082128
  2. 2

    Small fiber neuropathy with long-term, multifocal paresthesias after a SARS-CoV-2 vaccination.

    Finsterer J, Scorza FA, Scorza CA, de Almeida AG

    Clinics (Sao Paulo, Brazil) 2023; (78()):100186 doi:10.1016/j.clinsp.2023.100186.

    PMID: 36948070
  3. 3

    Small fiber neuropathy: Getting bigger!

    Chan AC, Wilder-Smith EP

    Muscle & nerve 2016; (53(5)):671-82 doi:10.1002/mus.25082.

    PMID: 26872938
  4. 4

    Central Sensitization and Small-fiber Neuropathy Are Associated in Patients With Fibromyalgia.

    Dumolard A, Lefaucheur JP, Hodaj E, et al.

    The Clinical journal of pain 2023; (39(1)):8-14 doi:10.1097/AJP.0000000000001085.

    PMID: 36524768
  5. 5

    Non-length-dependent small fiber neuropathy: Not a matter of stockings and gloves.

    Gemignani F, Bellanova MF, Saccani E, Pavesi G

    Muscle & nerve 2022; (65(1)):10-28 doi:10.1002/mus.27379.

    PMID: 34374103
  6. 6

    The Clinical Features of Painful Small-Fiber Neuropathy Suggesting an Origin Linked to Primary Sjögren's Syndrome.

    Zouari HG, Wahab A, Ng Wing Tin S, et al.

    Pain practice : the official journal of World Institute of Pain 2019; (19(4)):426-434 doi:10.1111/papr.12763.

    PMID: 30636091
  7. 7

    Small fiber neuropathy in children, adolescents, and young adults with chronic orthostatic intolerance and postural orthostatic tachycardia syndrome: A retrospective study.

    Moak JP, Ramwell CB, Gordish-Dressman H, et al.

    Autonomic neuroscience : basic & clinical 2024; (253()):103163 doi:10.1016/j.autneu.2024.103163.

    PMID: 38537312
  8. 8

    A case of erythromelalgia with gastrointestinal dysautonomia treated with immunoglobulin: A case report.

    Bourkas AN, Geng R, Sibbald M, Sibbald RG

    SAGE open medical case reports 2023; (11()):2050313X231213137 doi:10.1177/2050313X231213137.

    PMID: 38022850
  9. 9

    Investigation of nerve fibers in the skin by biopsy: technical aspects, indications, and contribution to diagnosis of small-fiber neuropathy.

    Raicher I, Ravagnani LHC, Correa SG, et al.

    Einstein (Sao Paulo, Brazil) 2022; (20()):eMD8044 doi:10.31744/einstein_journal/2022MD8044.

    PMID: 35830153
  10. 10

    Assessment of small fiber neuropathy and distal sensory neuropathy in female patients with fibromyalgia.

    Min HK, Im S, Park GY, Moon SJ

    The Korean journal of internal medicine 2024; (39(6)):989-1000 doi:10.3904/kjim.2024.038.

    PMID: 39468927
  11. 11

    Fibromyalgia: is it a neuropathic pain?

    Cheng CW, Wong CS, Hui GK, et al.

    Pain management 2018; (8(5)):377-388 doi:10.2217/pmt-2018-0024.

    PMID: 30212264
  12. 12

    Central sensitisation pain and autonomic deficiencies in fibromyalgia.

    Garcia-Hernandez A, de la Coba P, Reyes Del Paso GA

    Clinical and experimental rheumatology 2022; (40(6)):1202-1209 doi:10.55563/clinexprheumatol/n280oi.

    PMID: 35748717
  13. 13

    Advances in the Management of Small Fiber Neuropathy.

    Zeidman LA

    Neurologic clinics 2021; (39(1)):113-131 doi:10.1016/j.ncl.2020.09.006.

    PMID: 33223078
  14. 14

    Diagnostic Criteria for Small Fiber Neuropathy.

    Blackmore D, Siddiqi ZA

    Journal of clinical neuromuscular disease 2017; (18(3)):125-131 doi:10.1097/CND.0000000000000154.

    PMID: 28221302
  15. 15

    Current Diagnosis and Treatment of Painful Small Fiber Neuropathy.

    Farhad K

    Current neurology and neuroscience reports 2019; (19(12)):103 doi:10.1007/s11910-019-1020-1.

    PMID: 31773305
  16. 16

    Small fiber neuropathy in irritable bowel syndrome.

    Motaghi P, Adibi I, Adibi P, Ghasemi M

    Gastroenterology and hepatology from bed to bench 2024; (17(1)):57-63 doi:10.22037/ghfbb.v17i1.2827.

    PMID: 38737934

This page provides educational information about differentiating small fiber neuropathy from fibromyalgia. It does not replace professional medical advice. Always consult your doctor or neurologist for proper diagnostic testing and treatment.

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