Quantitative assessment and correlation of sympathetic, parasympathetic, and efferent small fiber function in peripheral neuropathy

We compared three neurophysiological methods for assessing small nerve fibe r function in 40 patients with peripheral neuropathy to determine the vario us manifestation types of peripheral small fiber neuropathy. Heart rate var iation tests were used to assess cardiac parasympathetic small fiber functi on. Cutaneous vasoconstrictor responses (sympathetic C fibers) induced by d eep inspiration were examined with laser Doppler flowmetry. Cutaneous affer ent C fiber function was assessed by measurement of axon reflex vasodilatat ion induced by histamine iontophoresis. All test parameters were significan tly lower in patients with peripheral neuropathy than in control subjects. Comparison of the three small fiber systems revealed that functionally diff erent systems are damaged independently, and isolated affection of each fib er type was frequently observed. The three tests are useful noninvasive too ls with which to evaluate sympathetic, parasympathetic, and afferent small fiber function in patients with peripheral neuropathy. In many patients fun ctionally different small fiber systems are affected selectively. To diagno se small fiber neuropathy and to evaluate the individual type of manifestat ion complementary testing of several small somatic and autonomic fiber syst ems is necessary.