Anyone reading this, please feel free to correct any mistakes. Here's my take on the issue:
Tabes dorsalis occurs in about 30% of untreated syphilis. Gummatous inflammatory lesions occur in the spinal cord, specifically in dorsal roots and meninges. It causes dystrophic changes of myelin and axons of thick sensitive fibers that pass through dorsal roots, specifically affecting fascicles gracilis (recall axon myelination proprioception > mechanoreceptors > sharp pain > dull pain).
Clinics in Dermatology Volume 23, Issue 6, November–December 2005, Pages 555–564
Pain in tabes dorsalis has been described as lightning and lancinating, sometimes occurring in a traveling or 'pulling' distribution (lower leg -> upper leg -> buttocks -> back).
Successful treatment of tabetic lightning pain and visceral crisis with gabapentin J Anesth. 2011 December; 25(6): 952.
I prefer to specify it as
allodynia (pain produced by a stimulus that would not normally produce pain) rather than
paresthesia (as paresthesia is 'alteration of sensation', not necessarily 'pain caused by a stimulus that would otherwise not cause pain'), although both terms are used. On a cellular level, allodynia is caused by inappropriate cross-communication between dermal mechanoreceptors (Meissner's corpuscles, specific for light touch) and Adelta/type III sensory fibers (specific for sharp pain), both of which go to dorsal roots. Here's where it gets a bit tricky: There are several theories as to how and why this cross-communcation happens, but the bottom line is that stimulation of mechanoreceptors in the skin either transmits pain sensation itself, or inappropriately activates nociceptors. (wiki: Allodynia)
In contrast to Fatalis' opinion, this wasn't as straightforward as he'd like to believe. Secondly, proprioceptive dysfunction occurs simultaneously with allodynia (
"Charcot joints" is a neuropathic arthritis, a severe form of osteoarthritis. The arthritic knee joints result from the relative insensitivity of the joints, due to destruction of the dorsal root fibers, and the resultant repeated injury; remaining pain fibers however were still sufficient to permit pain to occur. Charcot joints occur in less than 10 percent of tabes patients http://isc.temple.edu/neuroanatomy/lab/lesions/8.htm). Thirdly, and I've said this in another post, I absolutely appreciate asking questions because someone with prior knowledge will clarify it for you, or other people will realize they don't know it either. I personally have learned a whole lot from the responses to your questions.