LONGITUDINAL ASSESSMENT OF DIABETIC POLYNEUROPATHY USING A COMPOSITE SCORE IN THE ROCHESTER DIABETIC NEUROPATHY STUDY COHORT

Because there are little satisfactory data on change in severity of di abetic polyneuropathy (DP) over time from study of population-based co horts of diabetic patients in epidemiologic surveys of DP, it is diffi cult to predict outcome or morbidity or to identify risk factors; it i s also difficult to estimate statistical power for use in controlled c linical trials. In this longitudinal study of almost 200 patients from the Rochester Diabetic Neuropathy Study (RDNS) cohort, we assess whic h symptoms, clinical examinations, tests, or combinations of examinati ons and tests (composite scores) are best used as minimal criteria for the diagnosis of DP and as a quantitative measure of severity of DP. An abnormality (greater than or equal to 97.5th percentile) of a compo site score that included the Neuropathy Impairment Score of the lower limbs plus seven tests (NIS(LL)+7 tests), was a better minimal criteri a for DP than clinical judgment alone or previously published minimal criteria. First, it provided a more comprehensive assessment of neurop athic impairment. Second, it avoided the overestimated frequency of DP when the minimal criteria for DP was any one or two abnormalities fro m multiple measurements. Minimal criteria using nerve conduction and r educed heart beat response to deep breathing identified approximately twice as many patients with DP than did clinical examination and vibra tion detection threshold using CASE IV. This difference could be used to subclassify stage 1 DP. Although various individual measures of DP, for example, vibration detection threshold (as evaluated by CASE IV a nd the 4, 2, and 1 stepping algorithm [see text]), were good measures of worsening, the composite score NIS(LL)+7 tests (assessing neuropath ic impairment) was much better at showing monotone worsening. Using th is composite score, the average diabetic patient in the RDNS worsened by 0.34 points per year, whereas patients with diabetic polyneuropathy worsened by 0.85 points per year. On the assumption that a therapeuti c agent may prevent worsening of DP but not cause improvement, control led clinical trials of patients with DP would need to be conducted for a period of 3 years to achieve a meaningful change of 2 NIS points (t he level of abnormality considered by a Peripheral Nerve Society conse nsus group to be clinically meaningful).