I think that is just a general statement about injury...and nerves.
Many of the PN triggers are "toxic" in some way to the body.
When nerves get damaged by whatever, they release chemicals into the bloodstream, and it is believed that these may "spread" to other nerve pathways and cause inflammation.
One culprit is glutamate. When glutamate escapes from cells in the brain following a stroke, the damage can be extensive.
Also there is a risk of autoimmune response to any peptides released by nerve cells. Scientists are looking into this aspect for RSD/CRPS neuropathy.

There is a hereditary pressure palsy that may occur by itself however.
http://ghr.nlm.nih.gov/condition/her...essure-palsies