SURAL NERVE MYELINATED FIBER DENSITY DIFFERENCES ASSOCIATED WITH MEANINGFUL CHANGES IN CLINICAL AND ELECTROPHYSIOLOGIC MEASUREMENTS

New forms of therapy for diabetic and other neuropathies may prevent, stabilize, or ameliorate loss of nerve fibers. Clinically meaningful c hanges in mean Neurological Disability Score (NDS), and the associated mean change of electrophysiologic attributes have been described in d iabetic polyneuropathy. it is unknown what magnitude of myelinated fib er (MF) density change is associated with these meaningful changes of clinical and electrophysiologic alterations. In 18 diabetics and 5 nor mal controls associations between the mean NDS, summated (ulnar, peron eal and tibial) compound muscle action potential (Sigma CMAP), summate d (ulnar and sural) sensory nerve action potential (Sigma SNAP), sural SNAP, and MF density in the sural nerve, were assessed using linear r egression analyses. Values were corrected for age and sex. For a decre ase of: 2 points in the mean NDS (minimum clinically detectable change ), MF density decreased by approximately 200 fibers/mm(2) (p < 0.001) 1 mV in the mean Sigma CMAP (sum of the ulnar, peroneal and tibial CMA P amplitudes), MF density decreased by 160 fibers/mm(2) (p < 0.01) 1 m u V in the mean Sigma SNAP (sum of ulnar and sural SNAP amplitudes), M F density decreased by approximately 70 fibers/mm(2) (p < 0.001) 1 mu V in the mean sural SNAP, MF density decreased by approximately 150 fi bers/mm(2) (p < 0.01). Changes in sensory detection thresholds were al so associated with a measurable change in the MF density. A quantifiab le association exists between the magnitude of change in density of MF , and a meaningful alteration in mean NDS and various electrophysiolog ic parameters. Knowledge of this is needed to assess the statistical p ower of a clinical trial in which density of myelinated fibers is an o utcome measurement.