Methods for assessing diabetic polyneuropathy: validity and reproducibility of the measurement of sensory symptom severity and nerve function tests

The usefulness of sensory symptoms in the assessment of diabetic polyneurop athy is unclear. In the present study, we studied the hypothesis that pain is associated with small nerve fibre function, and that sensory alteration is associated with large nerve fibre function. In addition, we assessed the reproducibility and the ability to detect changes in clinical status over time of the nerve function tests currently used in clinical trials. Patient s (78) with stable diabetic polyneuropathy were examined on three separate occasions with a test-retest interval of 17 and 52 weeks. Small nerve fibre function was measured using temperature discrimination thresholds for warm th (TDTwarmth) and cold (TDTcold). Large nerve fibre function was measured by testing sensory and motor nerve conduction velocities (SNCV and MNCV) an d vibration perception thresholds (VPT). Neuropathic pain was only signific antly associated with TDTcold, and with the MNCV of the tibial nerve. Senso ry alteration was associated with almost all nerve function tests except th e SNCV and MNCV of the ulnar nerve. The measurements of symptom severity an d the nerve function tests all proved to be sufficiently reproducible. The standardized smallest detectable difference on group level (SDD) of the mea surement of sensory alteration and neuropathic pain were almost the same (9 % and 12%, respectively). Among the nerve function tests, the SNCV and MNCV had the smallest SDD (3-4%), and were, therefore, potentially the most res ponsive instruments. The SDD of the TDT was greater than the VPT (9-14% vs 21-28%, respectively). In conclusion, neuropathic pain was not associated w ith small nerve fibre function, and sensory alteration was associated with both large and small fibre function. In addition, the standardized measurem ent of symptom severity, the SNCV and MNCV tests, and the VPT test appear t o be useful for monitoring the course of polyneuropathy in clinical trials. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.