A skin punch biopsy counts the nerve fibers inside the epidermis and reports that count as intraepidermal nerve fiber density, or IENFD. A low count is objective evidence that the small sensory fibers are damaged — the fibers that carry pain and temperature, and the ones that produce burning feet while a standard nerve conduction study reads normal.
What the biopsy does not tell you is why those fibers are failing. That is the part that decides treatment, and it comes from the rest of the workup rather than from the number.
The test is used well beyond classic neuropathy presentations. Approximately 40% to 60% of patients carrying a diagnosis of fibromyalgia have evidence of small fiber neuropathy on skin punch biopsy.1
Regenerve performs the punch skin biopsy on site, so the sample is taken during a clinic visit rather than referred out.
How the test is done
A 3 mm punch is inserted into the biopsy site to take a small cylinder of skin, typically from the lower leg.1 The sample goes to a laboratory that stains the nerve fibers and counts how many cross into the epidermis per millimeter of tissue. That count is compared against reference values matched to site, age and sex.
It is a minor office procedure rather than a surgical one, and it samples the fibers directly instead of inferring their state from an electrical signal.
Why standard nerve testing can come back normal
Nerve conduction studies measure large myelinated fibers. Small fibers are unmyelinated or thinly myelinated and do not contribute to that signal, so they can be substantially damaged while the study reads normal.
Peripheral neuropathy is primarily diagnosed clinically, through history and neurological assessment of small fiber sensation with temperature or pinprick, large fiber sensation with vibration, and ulceration risk with 10 g monofilament pressure testing.2 Nerve conduction studies and intraepidermal nerve fiber density testing are indicated where there are atypical clinical features, such as rapid symptom onset, severe neuromotor impairment or asymmetrically abnormal sensation.2
Regenerve performs electrodiagnostic testing (EMG/NCS) on site, and reads it against the clinical picture rather than treating it as a verdict. A normal study in someone with burning feet is a reason to look at the small fibers, not a reason to stop looking.
A normal biopsy does not close the case
Using current normal values, epidermal nerve fiber density is abnormally decreased in only about two-thirds of patients suspected of having small fiber neuropathy.3 That means roughly one in three patients with a convincing clinical picture will have a biopsy that reads normal.
Reference ranges, sampling site and laboratory methodology all shift where the line between normal and abnormal falls. A single number in isolation is not a diagnosis, and a normal result in someone whose symptoms fit is a reason to widen the search rather than to stop.
What each result changes
- Low IENFD. Small fiber damage is confirmed. The question moves entirely to which driver is producing it.
- Normal IENFD with fitting symptoms. The clinical picture still stands. Alternative or overlapping mechanisms get evaluated, and the biopsy result is recorded rather than used to dismiss the complaint.
- Normal IENFD with an atypical picture. The differential widens beyond small fiber involvement.
The biopsy tells you the fibers are damaged, not what damaged them
Neuropathy is a category, not a diagnosis. Small fiber damage can arise from metabolic, nutritional, autoimmune, toxic or structural drivers, and it is common for more than one to be active at the same time.
That is where the evaluation actually lives — establishing which mechanism is doing the damage, then directing treatment at it. Our discussion of the contributors that most often get missed is in the hidden drivers of peripheral neuropathy.
Driver categories we work through
- Metabolic. Glucose handling, insulin resistance and glycation-related injury.
- Nutritional. Absorption problems and nutrient status, including after abdominal or bariatric surgery.
- Autoimmune. Systemic inflammatory and immune-mediated processes.
- Toxic. Medications, alcohol, chemotherapy exposure and environmental agents.
- Structural. Compression and mechanical contributors that can sit on top of any of the above.
What we do with the result
At Regenerve the biopsy result feeds into a plan built around the identified driver. That plan can include class 4 photobiomodulation, class 3B cold laser, whole-body infrared, and metabolic and nutritional care.
Orthobiologic injections (PRP and BMAC) are offered. Where balance complaints are part of the picture, VNG (videonystagmography) may be used as a diagnostic test of inner-ear balance function; it is not a treatment. Nothing offered here reverses or regenerates nerve damage, and no outcome is promised.
Questions worth asking before a biopsy
- What in my history makes small fiber involvement the leading suspicion?
- Which site will be sampled, and which laboratory and reference values will be used?
- What will change in my evaluation if the result is low?
- What is the next step if the result comes back normal but my symptoms do not?
Being evaluated in St. Louis
Regenerve is at 4477 Woodson Rd #104, St. Louis, MO 63134, minutes from St. Louis Lambert International Airport, and is led by Dr. Gurpreet Singh Padda, MD, MBA, MHP. The practice serves the St. Louis region, Missouri and Illinois.
Call or text (314) 886-5902, or email info@regenerve.com. Office hours are Monday through Thursday 9:00 to 16:00 and Friday 9:00 to 13:30.
If a nerve test came back normal and your feet still burn, the Nerve Damage Score is a free five-question assessment that produces a large-print report you can bring to any physician.
Frequently asked questions
What does a skin biopsy for small fiber neuropathy involve?
A 3 mm punch takes a small cylinder of skin, usually from the lower leg, and a laboratory counts how many nerve fibers cross into the epidermis per millimeter. It is an office procedure, not surgery. See the testing and services we provide.
How is it different from an EMG and nerve conduction study?
Nerve conduction studies measure large myelinated fibers; the biopsy counts the small fibers directly. That is why burning feet can coexist with a nerve conduction study that reads normal. See burning feet and nerve pain.
Can I have small fiber neuropathy if my biopsy is normal?
Yes. Using current normal values, epidermal nerve fiber density is abnormally decreased in only about two-thirds of patients suspected of having small fiber neuropathy, so a normal result does not exclude the diagnosis. See how to choose a neuropathy specialist.
If my biopsy is abnormal, what happens next?
The work shifts to identifying which driver is damaging the fibers — metabolic, nutritional, autoimmune, toxic or structural — because that is what determines treatment rather than the density number itself. See how sugar damages nerves.
Is this test only relevant to diabetes?
No. Small fiber damage shows up across nutritional, autoimmune and toxic drivers as well, and roughly 40% to 60% of patients carrying a fibromyalgia diagnosis have evidence of it on skin punch biopsy. See functional B12 deficiency and neuropathy.
Sources
- Kelley MA, Hackshaw KV. Intraepidermal Nerve Fiber Density as Measured by Skin Punch Biopsy as a Marker for Small Fiber Neuropathy: Application in Patients with Fibromyalgia. Diagnostics (Basel). 2021;11(3):536. PMID 33802768
- Bodman MA, Dreyer MA, Varacallo MA. Diabetic Peripheral Neuropathy. StatPearls. StatPearls Publishing. 2024. NCBI Bookshelf NBK442009
- Levine TD, Saperstein DS. Diagnosing Small Fiber Neuropathy Through the Use of Skin Biopsy. Practical Neurology. October 2009. practicalneurology.com