Wednesday, May 29, 2013

Sensory Nerves

Loss of Tactile Sensitivity

The anecdotal oral histories consistently report loss of tactile sensitivity in the denerved areas. Is this possible, given that sensory nerves are something separate from sympathetic nerves? Yes, because “sympathetic nerves are known to modulate sensory nerve function” (Merhi et al. 1998; see Khalil 1997).

Prediction: Thoracic sympathectomy will reduce tactile sensitivity in the denerved area.

Empirical status: Confirmed.

Back in the 1940’s, surgeons were using sympathectomy to treat a number of war-related problems, including causalgia. Causalgia is a burning pain sensation resulting from injury to sensory nerves, usually in the arms or legs. To begin figuring out if sympathectomy would be effective, the surgeons first injected anesthetic into the sympathetic ganglion. “The prompt relief of pain after the injection [into the sympathetic ganglion] was usually striking and conclusive” (Freeman 1955). This led the surgeons to use sympathectomy, both thoracic and lumbar, to alleviate pain.

The war surgeons had provided empirical confirmation for the physiological discoveries later made by Merhi, Khalil and colleagues: that the SNS has a strong role in the modulation of sensory nerves.
Mailies and Furlan conducted a 2002 review of sympathectomy in the treatment of pain syndromes. As Mailis explains, today “many neuropathic pain syndromes, particularly reflex sympathetic dystrophy and causalgia (currently called Complex Regional Pain Syndromes (CRPS), types I and II, respectively), are thought to be ’Sympathetically Maintained Pain’.” (Mailis et al. 2002)


Now let’s apply the principle of denervation super-sensitivity to the receptor cells in the sensory nerves. After they are denerved, it is expected that they will become super-sensitive to catecholamines. We can surmise that super-sensitivity induced on a sensory nerve would manifest as “pain”.

Prediction: Thoracic sympathectomy will induce chronic pain.

Empirical status: Confirmed.

Mailis again: “Furthermore, complications of [ETS surgery] may be significant, in terms of both worsening the pain or producing a new pain syndrome. . .” (Mailis et al. 2002, emphasis added). Mailis concludes “more clinical trials of sympathectomy are required to establish the overall effectiveness and potential risks of this procedure.” (Mailis et al. 2002). I too call for research into the role of the SNS in modulating sensory nerves, and the effect of ETS on sensitivity. Patients should be warned about potential loss of tactile sensitivity in the denerved area, and possible chronic nerve pain.


Loss of sympathetic drive to sensory nerves may also manifest as parestheia, which is experienced as a tingling or burning sensation. 17.6% of patients reported permanent paresthesia in a 2005 Chinese study.
Paresthetic discomfort distinguishable from wound pain was described by 17 patients (50.0%). The most common descriptions were of 'bloating' (41.2%), 'pins and needles' (35.3%), or 'numbness' (23.5%) in the chest wall. The paresthesia resolved in less than two months in 12 patients (70.6%), but was still felt for over 12 months in three patients (17.6%). Sihoe et al. 2005