In a skin punch biopsy, a small skin sample about 1/4-inch (3mm) wide is taken by a special tool. It is spring loaded and goes down, takes a sample from your skin and pop backs up leaving a small hole where it took the sample. I doesn't really hurt and your wound repairs in about a week.

Typically, to test for non-length dependent SFN, a biopsy is taken from your ankle or foot and compared to a biopsy taken from your thigh. Under a microscope, the density of small nerve fibers is examined in each biopsy area. The results usually take about 2 weeks since the biopsied skin sample is sent to a lab for analysis.

If the sample taken from your upper leg shows fewer healthy nerve endings than the sample from your ankle, it is a confirmation of "non-length dependent small nerve fiber neuropathy/neuronopathy." So it can confirm a diagnosis if this result happens. However, sometimes a sample for a person with NLDSFN has the same number of healthy nerve fibers in both areas (falling into the normal range). In this case, only a "soft" diagnosis can be made based on patient reports of pain. For example, when pain is reported in the hip and thigh but not the feet, it is evidence for a diagnosis of NLDSFN.

In summary, a punch biopsy can, but doesn't always, confirm NLDSFN.

Hope this helps.