Quantitative sudomotor axon reflex test (QSART): A new approach for testing distal sites

The quantitative sudomotor axon reflex test (QSART) is a useful tool in the evaluation of C-fiber function. Because many neuropathies show a length-de pendent loss of nerve function, a new capsule was designed for distal perfo rmance of the QSART, allowing measurements on fingers and toes. We investig ated 20 healthy volunteers and 15 patients with insulin-dependent diabetes mellitus and normal sensory nerve conduction studies. A QSART was performed on the forearm and on the thumb. The groups showed no differences in the Q SARTs on the forearm, but the sweat volume on the thumb was significantly l ower in patients. Calculation of the forearm/finger ratio reduced the inter individual variation and showed the highest sensitivity for detecting C-fib er dysfunction in the patient group. We conclude that the distal measuring device and the forearm/finger ratio are more sensitive tools for the early detection of distal-onset neuropathies than are the commonly used proximal testing sites. (C) 1999 John Wiley & Sons, Inc.