--for detecting small-fiber damage.

It was the only "positive" or "abnormal" test (nearly two hundred results' pages worth) I ever had--and I had an acute onset, full-body, burning/stinging neuropathy with very high pain levels.

However, owing to the protocols by which "damage" is determined--basically that one be either below the fifth percentile or above the ninety-fifth percentile in intraepidermal nerve fiber density (as determined from a group of "normals" originally research primarily through Johns Hopkins Medical Center in Baltimore, MD), it may not catch all people who have a developing small-fiber neuropathy, or who have damage from their own normal density but not sufficient to place them above or below those percentiles. To be sure, good pathologists will also look at the condition of the nerves, particularly if there is swelling or excessive branching of fibers, as these are indicative of some dysfunctional process.

There are more and more cases, though, of people with neuropathic symptoms for which this is the only abnormal test, and they are still considered idiopathic. (Many people with diabetic, pre-diabetic, or vasculitic/autoimmune neuropathy will also show small-fiber damage on skin biopsy.)

This link is a very good summary of the utility skin biopsy in determining neuropathy, with a great reference list for further reading (you may have to set up an account and log in, but it's free):

http://www.medscape.com/viewarticle/563262_1

BTW, as regards spinal conditions, don't assume that cervical problems cannot lead to symptoms below the waist. Depending on the situation and the anatomy involved, spinal problems can lead to symptoms at any anatomical level at or below the level they occur at--and it's why those with neuropathic symptoms are often very hard to interpret and narrow down the cause of, as symptoms of a peripheral neuropathy and/or a spinal/nerve root problem may be exactly the same.