Effects of mechanical irritation on the autonomic part of the median nerve

The diagnosis of median nerve compression is generally based upon a prolonged nerve conduction velocity although this frequently is preceded by clinical symptoms for years. The present study was designed to identify indicators for early decompression of the median nerve in patients exhibiting symptoms compatible with carpal tunnel syndrome (CTS). Microvascular perfusion in finger tip skin and skin temperature were studied during dorsiflexion of the hand prior to and following a manual exercise test in control subjects and in patients with clinical symptoms and signs of CTS. Evaluation of the microcirculation was performed using photoplethysmography (PPG) and laser Doppler fluxmetry (LDF). Fingertip skin temperature was measured by thermography and was significantly reduced in patients after exercise (P < 0.001), whereas no significant change occurred in control subjects. During increasing degrees of dorsiflexion (0-75 degrees ) and after manual exercise, fingertip skin perfusion remained unchanged in both patients and control subjects. In conclusion, patients with low-grade CTS experience skin temperature reduction, presumably caused by increased sweating as opposed to a generally suspected vasoconstriction. These autonomic median nerve dysfunctions provide the physiological basis for the use of thermography in confirming low-grade CTS.