I saw something Red posted about Arachnoiditis. It may be an explanation of how we get neuralgia in more than one nerve. What he posted describes how bunches of nerves can get bound together by scar tissue and loss of the myelin sheath, so the pain in 1 of the nerves may spread to others in the bunch. He said:
"As you know, arachnoiditis is characterized by multiple nerve adhesions and impingements of non-vascular structures adjacent to the trigeminal and other cranial nerves. In some patients, these adhesions can extend through large sections of the brain proper. Although not all of the mechanisms which cause ATN are fully known or analyzed, Peter and one other neurosurgeon I talked lwith felt that the disturbance of the myelin layer around the nerve due to "mashing" (my term, not the doctors) in an adhesion might be enough to cause adjacent nerve fibers within the nerve to communicate with each other in a manner that can cause sustained burning pain downstream of the adhesion. The pain response is similar to that experienced by MS patients with plaques on the nerve, but is associated with a more diffuse and extended region of contact between the nerve and adjacent structures -- and with the filmy substance of the adhesion tissue itself."
(June 24, 2011 on AliBaby'scomment page)