Since PN is so variable with over 100 causes, it can present very differently from person to person.

Dr. Latov who is a PN specialist in New York has a list of tests he uses to find causes:

http://www.questdiagnostics.com/test...ripheralNeurop

Basically there are 3 points of view. People can have mixtures of these as well. This is only a partial listing:
1) exposure to things in the environment and lifestyle, drugs, toxins, vaccine exposure, solvents (including manicure solvents and fumes), pesticides, heavy metals, clothes cleaning fluid residues, furniture strippers, printing solvents, injuries and repetitive strain, etc.

2) some internal medical issue that is causing a secondary problem such as pre-diabetes (impaired glucose intolerance and frank diabetes), hypothyroidism, paraneoplastic (cancer) issues, autoimmune reactions like Sjogren's and Lupus, nutrient deficiencies like B12, B1, B6, nutrient toxicity (excess B6), Gluten intolerance, other food intolerances, etc., compression or disease(arthritis) in the ankle, knee and/or spine, etc.

3) hereditary issues, which for the most part are inherited, CMT.
However, this presents in a confusing pattern, that is highly individualistic, and now some papers are coming forward showing CMT can be latent and brought on by drugs such as Levaquin, which somehow trigger it.

Rapidly progressing neuropathies often begin to affect motor ability with weakness in muscle groups developing. Many doctors in US will try IVIG on these types because it is suggestive of autoimmune issues.

So with all these variables it is almost impossible to compare people to each other. And with the huge list of possibilities doctors will not test for everything typically. They will wait and see what develops. It can become very expensive, and time consuming and so they may proceed slowly or not at all in some cases (sad but true).