Originally Posted by glenntaj

The only way the result could have been determined is by comparison with "normal" ranges.

I've written a lot about this before--I think the normal ranges are rather arbitrarily set. There is considerable variation in nerve fiber density among asymptomatic people, which was discovered when they first started doing this at Johns Hopkins a few decades ago. So the range of normal was set at between 5% and 95% density levels of all the subjects they tested. People with density levels below 5% and above 95% are considered to be positive for small fiber neuropathy.

The problem with this is that one seldom has any idea of what level one was at BEFORE symptoms--almost no one goes in for skin biopsy until there are symptoms. Suppose one started at around the 50th percentile (though one would not know this, generally). One has a skin biopsy and the results show the density at around the 20th percentile. This would be listed as "normal", but it might well represent a significant dimunition from that person's "normal" level.

This is part of the reason why they are also supposed to report the condition of nerves--if there are swellings, excessive branchings, evidence of inflammatory infiltration. It's also why often multiple skin biopsies with numbers tracked can be informative--one looks for the trend.