Skin biopsy negative?
 

I got back the results of my skin biopsies and they were negative. The neurologist was convinced I had SFN, but asked if I wanted to confirm the diagnosis.

Since the skin biopsies were negative as well as the EMG being negative, he has now changed his diagnosis to post viral syndrome. I am now on an antiviral medication for a month to see if I improve.

Can there be a possibility that the skin biopsy produced a false negative? I’m wondering if the result would be different from a different area.

You'd really need to see--
 

--the specific report on the skin biopsy to get a better sense of this.

Back when the skin biopsy protocols were being developed at Johns Hopkins with so-called "normal" subjects without neuropathic symptoms, it was rather arbitrarily decided that those with intraepidermal nerve fiber densities above the 95th percentile and below the 5th percentile of those normed averages would be considered to have definitive evidence of small fiber neuropathy. The problem is that even people without symptoms have considerable variation in the number of fibers per cubic millimeter of skin and since no one goes for a skin biopsy, generally, without symptoms one may not know where one "started" and whether the result represented a decrease or increase from their own "normal" state.

The reports are also supposed to indicate what the condition of the fibers found are--whether they are swollen, give indication of deterioration or excessive branching, etc.--which can be indications of a systemic condition.

Fortunately, since the procedure is pretty much non-invasive, it can be repeated over time for the sake of comparison and one can see if there are increases/decreases/changes in nerve condition. But I wouldn't just take a blanket "negative" result at face value without seeing the report.

Does the location of the skin biopsy matter?
 

The skin biopsy was not taken from the exact area. My symptoms are mostly in the front of my legs and arms, but the doctor took the biopsies from the side of my leg and thigh.