For patients

Numbness, burning and tingling: peripheral neuropathy

The nerves that fail first are the smallest ones, and they are the ones a standard nerve test is least able to see.

Two different kinds of nerve

Peripheral nerves come in two broad classes and they fail in a different order.

	Large myelinated fibers	Small unmyelinated fibers
What they do	Vibration, position sense, muscle strength, reflexes	Pain, temperature, sweating, blood-vessel tone in the skin
How they are tested	Nerve conduction studies and electromyography	Sudomotor testing, skin biopsy, quantitative sensory testing
When they are affected	Usually later	Usually first

This matters more than it sounds. If someone has burning feet and a normal nerve conduction study, the common conclusion is that nothing is wrong. The more likely explanation is that the small fibers are affected and the test used does not measure them. Sudomotor testing is one of the practical ways to measure the small fibers without a biopsy.

The symptoms people describe

• Burning in the feet, worse at night and often worse under the bedcovers.
• Pins and needles, or a feeling of walking on gravel or on a wrinkled sock.
• Numbness that started at the toes and moved slowly upward in a stocking pattern.
• Skin that no longer sweats normally — either dry and cracked, or sweating in the wrong places.
• Loss of the ability to tell hot from cold in the feet.
• Balance that is worse in the dark or with eyes closed.

Why it is worth measuring rather than waiting

Nerve injury associated with impaired glucose tolerance and metabolic syndrome preferentially affects the small fibers, and nerve conduction studies are relatively insensitive to it, which is why intraepidermal nerve fiber density on skin biopsy is often used to confirm the diagnosis. The practical consequence is that people can have measurable small-fiber injury while their blood sugar is still classified as prediabetic and their nerve studies read normal.

The American Diabetes Association’s position statement on diabetic neuropathy is explicit that screening should not wait for symptoms, and that a substantial proportion of neuropathy is painless — the people at highest risk of a foot injury are often the ones who feel the least.

What causes it besides diabetes

Diabetes is the most common cause in this country but it is not the only one. Thyroid disease, kidney disease, vitamin B12 deficiency, alcohol, certain chemotherapy agents, autoimmune conditions, and hereditary neuropathies all produce a similar picture. Part of the reason the suite includes laboratory panels is to separate the reversible causes from the ones that need a different plan.

Related: sudomotor dysfunction and autonomic symptoms.

If you are a clinician: the same subject written for the person ordering the test is at the clinical rationale.

Common questions

My nerve test was normal but my feet still burn. What now?

A normal nerve conduction study rules out large-fiber disease, not small-fiber disease. The next measurement is a small-fiber one. Small-fiber versus large-fiber neuropathy.

Why is it worse at night?

Small-fiber pain characteristically intensifies at rest and at night, which is one of the features that distinguishes it. Burning feet at night.

Can neuropathy be reversed?

Where an underlying driver such as glucose intolerance, B12 deficiency or thyroid disease is found and corrected, improvement is possible. Where nerve loss is long-standing it is usually about halting progression. What comes before diabetes.

Do I need a skin biopsy?

Not usually as a first step. Non-invasive small-fiber measurement comes first, and biopsy is reserved for cases where it will change the plan. What is measured non-invasively.

References

• Cortez M, Singleton JR, Smith AG. Glucose intolerance, metabolic syndrome, and neuropathy. Handbook of Clinical Neurology. 2014;126:109–122. doi:10.1016/B978-0-444-53480-4.00009-6
• Pop-Busui R, Boulton AJM, Feldman EL, et al. Diabetic Neuropathy: A Position Statement by the American Diabetes Association. Diabetes Care. 2017;40(1):136–154. doi:10.2337/dc16-2042

Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP, medical director of Measura. Last reviewed August 20, 2026.