--with the skin biopsy results is that the definitions of "normal" and "abnormal' were rather arbitrarily set by MacArthur and his colleagues at Johns Hopkins when this was first investigated as a way to detect small-fiber neuropathies (which are very difficult to detect, as there may be no other abnormal test results, including normal nerve conduction and electromyography studies).

The Hopkins researchers did skin biopsies on a range of what were assumed to be people with normal nerve fiber densities and found that there was a wide range of fiber density even in asymptomatic individuals. After playing with the statistics for a while, they designated those who had nerve fiber density levels below the fifth percentile and above the ninety-fifth percentile as being "abnormal".

I'm fairly convinced that those with nerve fiber densities in those areas have something going on, but I also think one can have neuropathies even within that "normal" middle range. The trick is that one doesn't usually know at what density levels one started at before symptoms. As Echoes implies, one can move a lot within the normal range over time, and to me that's an indication of something going on. If one was at the sixtieth percentile in young adulthood, say, and then after symptoms is in the twentieth percentile, one is still technically "normal", but that reduction implies some neuropathic process.

This is also why one needs a neurologist familiar with these protocols to interpret. They are also supposed to note the condition of the fibers, not just density--are they swollen/inflamed, is there excessive branching, are there signs of autoimmune degeneration.