Neuromuscular Medicine

Overview

Peripheral neuropathy means injury or dysfunction of nerves outside the brain and spinal cord. It is a pattern, not a single disease. Symptoms can include numbness, burning pain, tingling, imbalance, weakness, cramps, and autonomic problems involving blood pressure, sweating, digestion, bladder function, or heart rate.

The most useful question is not simply “Do I have neuropathy?” but what type, distribution, tempo, and cause. A slowly progressive length-dependent sensory neuropathy has a different workup from sudden asymmetric weakness, a painful mononeuropathy, or rapidly evolving autonomic failure.

The major evidence messages in 2026 are:

• High-yield laboratory testing is focused. For distal symmetric polyneuropathy, glucose testing, vitamin B12 with metabolites when appropriate, and serum protein immunofixation are among the highest-yield tests; additional studies depend on the history.¹
• Normal nerve-conduction studies do not exclude small-fiber neuropathy. Skin biopsy and autonomic testing can support selected cases, but results must be interpreted with clinical symptoms and examination.²⁶
• Treatment should target the cause and the symptoms. Pain medicines reduce discomfort but do not automatically repair nerve damage.³
• Supplements can cause neuropathy. Excess vitamin B6 from overlapping multivitamin, magnesium, zinc, energy, or “nerve support” products is an underrecognized cause.⁵
• Some formerly untreatable inherited neuropathies now have disease-directed therapy. Wainua (eplontersen) is FDA-approved for adult polyneuropathy of hereditary transthyretin-mediated amyloidosis, but it is not a general neuropathy drug.⁴

Evidence cutoff: This article reflects publicly available evidence through July 10, 2026. Rapid weakness, breathing or swallowing difficulty, severe autonomic symptoms, or bowel/bladder dysfunction requires urgent assessment.

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Large-Fiber, Small-Fiber, Motor, and Autonomic Patterns

Many neuropathies affect more than one fiber type. “Small-fiber neuropathy” should not become a catch-all diagnosis for every burning or autonomic symptom; objective and clinical evidence should fit.

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Common Causes

• Diabetes and prediabetes
• Alcohol exposure
• Vitamin B12 deficiency and vitamin B6 toxicity
• Kidney, liver, or thyroid disease
• Chemotherapy and other medications or toxins
• Monoclonal gammopathy, amyloidosis, or cancer-associated disease
• Autoimmune or inflammatory neuropathy
• Infection, including selected HIV, hepatitis, or Lyme presentations
• Hereditary neuropathy
• Nerve compression or entrapment
• Idiopathic neuropathy after an appropriate evaluation

Age-related symptoms should not be assumed to be “just aging.” Conversely, not every abnormal laboratory result is causal. The clinician must match cause, pattern, and timing.

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Urgent Patterns

Urgent neurological assessment is warranted for:

• Weakness progressing over days or weeks
• Difficulty breathing, swallowing, or holding up the head
• New inability to walk or rapidly worsening falls
• Marked asymmetry, severe focal pain, or multiple individual nerve injuries
• Prominent orthostatic fainting, urinary retention, or severe autonomic failure
• Neuropathy with fever, rash, weight loss, cancer, or systemic inflammation
• Symptoms after a new medication, toxin, or immune treatment

These patterns raise concern for Guillain–Barré syndrome, vasculitic neuropathy, CIDP, amyloidosis, paraneoplastic disease, toxic neuropathy, spinal-cord disease, or another condition requiring prompt treatment.

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Diagnosis

History and examination

Clinicians assess distribution, progression, pain quality, weakness, reflexes, gait, autonomic symptoms, family history, medications, supplements, alcohol, occupational exposures, chemotherapy, and systemic disease.

Nerve-conduction studies and EMG

These tests evaluate large myelinated sensory and motor fibers, localize injury, and distinguish axonal from demyelinating patterns. They can separate polyneuropathy from radiculopathy, plexopathy, entrapment, motor-neuron disease, or muscle disease. They can be normal in isolated small-fiber neuropathy.

High-yield laboratory testing

For a typical distal symmetric polyneuropathy, common high-yield studies include fasting glucose or hemoglobin A1c, vitamin B12 with methylmalonic acid when indicated, and serum protein electrophoresis with immunofixation. A glucose-tolerance test may identify impaired glucose handling when routine glucose tests are nondiagnostic. Blood count, metabolic panel, thyroid testing, and other studies are chosen according to context.¹

Broad autoimmune, genetic, infectious, or paraneoplastic panels are not automatically appropriate. Targeted testing reduces false positives.

Small-fiber and autonomic testing

Skin biopsy measures intraepidermal nerve-fiber density. A reduced value supports small-fiber neuropathy but does not identify the cause and is not perfectly sensitive or specific. Autonomic tests such as QSART, cardiovagal testing, adrenergic testing, or tilt-table evaluation are selected according to symptoms and require appropriate technique and interpretation.²⁶

Genetic testing

Genetic testing is appropriate when there is a suggestive family history, childhood or young-adult onset, foot deformity, long-standing motor-predominant disease, unexplained amyloidosis features, or another recognizable phenotype. A negative family history does not exclude a hereditary neuropathy.

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Treat the Cause

• Diabetes: improve stable glycemic control and address cardiovascular, kidney, eye, and foot risk.
• Nutritional or toxic: correct deficiency or stop the causative exposure safely.
• Immune neuropathy: IVIG, corticosteroid, plasma exchange, or other immunotherapy only for a defined immune disorder.
• Entrapment: splinting, activity change, injection, or surgery depending on severity.
• Hereditary transthyretin amyloidosis: disease-modifying therapy and multisystem care. Wainua lowers transthyretin production and requires vitamin A counseling and monitoring according to its label.⁴

Unproven “nerve regeneration” infusions, stem-cell products, detox regimens, and high-dose vitamins should be approached cautiously.

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Treat Neuropathic Pain and Protect Function

Evidence-supported medication classes include gabapentinoids, SNRIs, tricyclic antidepressants, sodium-channel blockers, and selected topical therapies. Choice should reflect sleep, mood, kidney function, fall risk, weight, cardiac status, drug interactions, and patient preference.³

The AAN guideline recommends against starting opioids, including tramadol and tapentadol, for painful diabetic neuropathy because harms outweigh the modest and uncertain long-term benefit.³

• Physical therapy for balance, strength, gait, and fall prevention
• Occupational therapy and hand/foot adaptations
• Foot inspection, podiatry, and protective footwear when sensation is reduced
• Assistive devices or ankle-foot orthoses for weakness
• Sleep and mood treatment as part of pain care

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The Vitamin B6 Trap

Vitamin B6 is often present in multiple supplements at once. Excess exposure can cause sensory neuropathy, sometimes at doses patients do not recognize as high because products are combined. Review every label for pyridoxine, pyridoxal-5-phosphate, or related forms rather than assuming a “nerve vitamin” is harmless.⁵

Do not stop a medically prescribed product or begin high-dose replacement without clinician guidance; both deficiency and excess can be harmful in the right context.

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A Practical Framework

1. Define the pattern and urgency.
2. Use EMG/NCS for large-fiber localization and small-fiber tests selectively.
3. Order high-yield labs before indiscriminate panels.
4. Treat a proven cause whenever possible.
5. Protect feet, balance, sleep, and function while managing pain.

Bottom line: peripheral neuropathy has many causes and phenotypes. A precise diagnosis matters because treatment ranges from risk-factor control and pain relief to urgent immune therapy or disease-modifying treatment for a specific inherited condition.

At Los Altos Neurology, evaluation includes neurological examination, electrodiagnostic testing, focused laboratory workup, small-fiber or autonomic testing when appropriate, genetic assessment, and individualized symptom management.

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References

1. England JD, Gronseth GS, Franklin G, et al. Practice parameter. Neurology. 2009. AAN evidence-based review: Laboratory testing in distal symmetric polyneuropathy.
2. Katzberg HD, So YT, Brannagan TH, et al. AANEM Small Fiber Neuropathy Task Force. 2026. AANEM evidence review: Diagnostic and screening tests for small fiber neuropathy.
3. Price R, Smith D, Franklin G, et al. Neurology. 2022;98:31-43. AAN guideline: Oral and topical treatment of painful diabetic polyneuropathy.
4. U.S. Food and Drug Administration. Revised April 2026. WAINUA prescribing information.
5. Therapeutic Goods Administration. Safety communication. Vitamin B6 and peripheral neuropathy safety update.
6. American Association of Neuromuscular & Electrodiagnostic Medicine. AANEM proper performance of autonomic function testing.

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