# small fiber neuropathy | Symptoms, Causes, Tests and Treatment | OSANG > Small fiber neuropathy occurs due to pre-diabetes, immune disease, genetic disease, or unknown cause, and causes chronic pain and autonomic dysfunction. Standard electro… - Official page: https://osns.co.kr/en/encyclopedia/small-fiber-neuropathy - Organization: OSANG Neurosurgery ## Page content Neurological Conditions ## small fiber neuropathy Small Fiber Neuropathy · G60.8 Small fiber neuropathy (SFN) is a neuropathy in which myelinated Aδ fibers and unmyelinated C fibers (small fibers) among peripheral nerves are selectively damaged. The main symptoms are burning pain, stabbing pain, and paresthesia, and it is characterized by no abnormalities in standard nerve conduction tests. ## At a glance Small fiber neuropathy occurs due to pre-diabetes, immune disease, genetic disease, or unknown cause, and causes chronic pain and autonomic dysfunction. Standard electromyography (EMG) and nerve conduction tests show normal findings and are often misdiagnosed or misdiagnosed as psychogenic diseases. Measurement of intraepidermal nerve fiber density (IENFD) by punch biopsy is the gold standard for diagnosis. - 01Definition and Overview - 02Causes and classification - 03symptoms - 04diagnosis - 05treatment ## Definition and Overview Small fiber neuropathy (SFN) is a neuropathy in which thin myelinated Aδ fibers (1-6 μm in diameter) and unmyelinated C fibers (diameter <1 μm), which transmit pain and temperature sensations, are selectively damaged among peripheral nerves. Because large fibers (which transmit touch, vibration, and deep tendon reflexes) are preserved, standard electromyography and nerve conduction tests do not show abnormalities, and diagnosis is often delayed. The prevalence is estimated to be about 53 people per 100,000 people, and it occurs most often in people in their 40s and 60s. Small fiber neuropathy involves not only peripheral pain fibers (sensory fibers) but also autonomic nerve fibers, causing various autonomic symptoms. ## Causes and classification ### Classification by cause - Metabolic: diabetic neuropathy, pre-diabetes (impaired fasting glucose or impaired glucose tolerance), hypothyroidism - Immune/autoinflammatory: Sjögren's syndrome, lupus, rheumatoid arthritis, sarcoidosis, celiac disease - Heritability: SCN9A (Nav1.7), SCN10A (Nav1.8), SCN11A (Nav1.9) voltage-dependent sodium channel gene mutations - After infection: HIV, hepatitis B and C, aftereffects of COVID-19 (Long COVID) - Related to anti-cancer treatment: oxaliplatin, paclitaxel, etc. - Idiopathic (unknown cause): accounts for approximately 50% ## symptoms ### sensory symptoms Symptoms of small fiber neuropathy usually have a glove-stocking distribution that starts in both feet and progresses gradually upward. - Burning pain: persistent, burning pain in the feet - Stinging pain, electric shock sensation - Allodynia: Pain even with light touch (socks, bedding) - Numbness, numbness, hot and cold paresthesia Symptoms tend to get worse at night and may be worse with warmth (such as a hot shower) or in the heat. ### autonomic symptoms Since small fibers also include autonomic nerve fibers, the following symptoms appear when autonomic nerve small fibers are damaged. - Sweating abnormalities (anhidrosis or hyperhidrosis) - Orthostatic hypotension - Tachycardia - Gastrointestinal motility abnormalities (constipation, nausea) - bladder dysfunction ## diagnosis ### Skin Fiber Biopsy (Punch Biopsy) Measurement of intraepidermal nerve fiber density (IENFD) is the gold standard for diagnosing small fiber neuropathy. A small amount of skin is collected from 10 cm above the ankle and upper thigh, stained with PGP9.5 antibody, and the number of nerve fibers is measured. If the IENFD is below the 5th percentile of the normal reference value (relative to age and gender), the diagnosis is consistent. ### Quantitative Sensory Testing (QST) Small-fiber paresthesia is evaluated by quantitatively measuring hot and cold sensations and pain thresholds. ### Autonomic function test Autonomic nerve fiber function is assessed using heart rate variability (HRV) and quantitative sweat axon reflex testing (QSART). ### Blood tests and genetic tests Fasting blood sugar, glycated hemoglobin (HbA1c), 75g oral glucose tolerance test (OGTT), autoantibody (ANA, anti-SSA/SSB), thyroid function, and SCN9A/SCN10A gene analysis are used to identify the cause. ## treatment ### Cause Treatment If pre-diabetes is the cause, lifestyle changes (exercise, weight loss) and blood sugar control may help restore nerve fiber density. In immune-mediated small fiber neuropathy, immunoglobulin (IVIG) and steroid treatment may be effective. ### Neuropathy Pain Medication Treatment Primary drug: - Tricyclic antidepressants (amitriptyline): Useful in controlling nighttime pain. - SNRI (duloxetine, venlafaxine): Control of pain and autonomic symptoms - Gabapentin, Pregabalin: Control of neuropathic pain Topical treatment: - Lidocaine 5% patch or gel - Capsaicin 8% patch: High concentration of capsaicin desensitizes C fibers ### Management of autonomic symptoms For orthostatic hypotension and abnormal sweating caused by autonomic nerve fiber involvement, autonomic nerve function treatment according to the cause is provided in parallel. ## Frequently asked questions ### Q01What are the symptoms of small fiber neuropathy? It is characterized by burning pain, stabbing pain, and electric shock-like pain that starts in the feet and hands. Painful allodynia and tingling sensations occur even with light touch (socks, blankets). If autonomic nerve fibers are also involved, abnormal sweating, orthostatic hypotension, abnormal gastrointestinal motility, and abnormal bladder function may occur. ### Q02Why does small fiber neuropathy show up as normal on a regular electromyogram? Standard nerve conduction studies (EMG/NCS) evaluate the function of myelinated large fibers (Aβ fibers). In small fiber neuropathy, unmyelinated C fibers and thin myelinated Aδ fibers are damaged, resulting in normal findings on standard tests. Diagnosis requires skin biopsy for small nerve fiber density (punch biopsy) or quantitative sensory testing (QST). ### Q03Are small fiber neuropathy and fibromyalgia different? Fibromyalgia and small fiber neuropathy overlap significantly clinically. According to studies, a decrease in small nerve fiber density in the skin was confirmed in approximately 49% of fibromyalgia patients. Small fiber neuropathy is characterized by objective histological abnormalities (reduced IENFD), whereas fibromyalgia is distinguished by a central sensitization mechanism without tissue abnormalities. In some cases, both diagnoses occur together. ### Q04What causes small fiber neuropathy? Diabetes or pre-diabetes (impaired fasting glucose, impaired glucose tolerance) is the most common cause. Other diseases include immune diseases (Sjögren's syndrome, lupus, rheumatoid arthritis), SCN9A/SCN10A gene mutations, hypothyroidism, HIV, anticancer treatment (chemoneuropathy), and unknown cause (idiopathic). ### Q05Is small fiber neuropathy treatable? If the cause is identified (pre-diabetes, immune disease, etc.), treatment of the cause is important to inhibit the progression of nerve fiber damage. Gabapentin, pregabalin, tricyclic antidepressants, and SNRIs are used to control symptoms. Studies have shown that immunoglobulin (IVIG) treatment is effective in immune-mediated small fiber neuropathy. ## Related articles - delirium - Cervical radiculopathy - Cervical disc herniation - dystonia This article provides general medical information and does not replace an individual diagnosis or treatment plan. Please seek a medical assessment if symptoms persist. ## Important notice This Markdown alternative helps search and AI tools understand the public page accurately. It provides general health information and does not replace an individual diagnosis or treatment.