Validation of Michigan neuropathy screening instrument for diabetic peripheral neuropathy

The reliability and accuracy of the Michigan neuropathy screening instrument (MNSI) have been discussed recently. As a result of the difficulties of performing and analyzing nerve biopsy as a standard diagnostic test, electromyography and neuronography is used as the best alternative diagnostic procedure. The objective of this study was to determine the diagnostic performance of the test characteristics and cut-off point of MNSI scoring for the diagnosis of diabetic peripheral neuropathy.

Over a 2-year period, a cross-sectional study was conducted on 176 type 2 diabetic patients. An internist carried out the MNSI and the sum of scores varying from 0 to 1 for each abnormality as revealed in foot appearance, ulceration, ankle reflexes and vibratory perception has been recorded. A neurologist, who was blind to the MNSI scores, performed all neurophysiological studies. The test performance characteristics of the MNSI procedure were measured for different cut-off values.

MNSI scores of 1.5, 2.0, 2.5 and 3.0 were assessed as cut-off values. Sensitivities were 79%, 65%, 50% and 35% and specificities were 65%, 83%, 91% and 94%, respectively. Positive predictive values increased and negative predictive values decreased for each score. Accuracies, likelihood ratios and post-test probabilities were measured.

The accuracy of MNSI scoring makes it a useful screening test for diabetic neuropathy in taking a decision regarding which patients should be referred to a neurologist for electrophysiological studies. High specificity, likelihood ratios over 5 and a moderate to good post-test probability give a high diagnostic impact for MNSI scoring. We suggest a cut-off point of 2 for the MNSI procedure. However, electrophysiological studies should be considered when the patient has signs and symptoms other than those rated by the MNSI, suggesting peripheral nerve involvement, and also because the MNSI is still just a screening test.