--certain types of small-fiber syndromes are very hard to find. In fact, in my case, the ONLY test that was abnormal and revealed that there was a reason for feeling the burning all over my body that I was having was the abnormal skin biopsy which showed significant reduction in intrepidermal nerve fiber density.
You should take a look at:
http://www.thecni.org/reviews/13-2-p07-treihaft.htm
--which is an excellent article about small-fiber neuropatheis and the difficulty of diagnosing them.
I'd also look through the Liza Jane spreadsheets, which are lists of tests for neurological problems (with the abiliyt to track results over time, to look for patterns), and the Poncelet and Latov testing protocols:
www.lizajane.org
http://www.aafp.org/afp/980215ap/poncelet.html
http://www.questdiagnostics.com/hcp/...eralNeurop.htm