Stimulation of sudomotor axon reflex mechanism by carbachol in healthy subjects and patients suffering from diabetic polyneuropathy

Abstract

Sudomotor axon reflex (SAR) mechanism was stimulated by percutaneous iontophoresis of carbachol in healthy subjects and patients suffering from diabetic polyneuropathy (PNP) of differing severity (stage I-III). SAR response was assessed by hygrometry and compared with histamine induced neurogenic vasodilation (laser-Doppler flowmetry) and itching sensation (visual analogue scale), which may provide information on neuro-secretion and afferent function of nociceptive unmyelinated nerve fibers. Carbachol induced long lasting SAR response with maximal sweating rates 20-30 minutes after stimulus onset. In diabetic patients the carbachol induced SAR response and the histamine induced itching sensation were significantly reduced in stage III of PNP. In contrast, histamine induced vasodilatation was significantly impaired in all stages of PNP. It is concluded that prolonged SAR response following iontophoresis of carbachol can simplify evaluation of sudomotor function when compared to established tests using intradermal application of acetylcholine. Furthermore, to demonstrate impairment of unmyelinated nerve fibers in PNP, histamine induced vasodilatation was found to be more sensitive than SAR response.