Nerve ischaemia-resistance: an early abnormality in diabetes

Vibration perception threshold (VPT) has been measured before and 30 min after limb ischaemia in 17 newly diagnosed non-insulin-dependent diabetic patients and matched controls. Mean baseline VPT was higher in the diabetics than in controls (14 vs 11, p less than 0.01) while VPT at 30 min was lower (25 vs 30, p less than 0.05). The ischaemic index (VPT at 30 min/baseline VPT), calculated as a measure of nerve ischaemia-resistance, was lower in the diabetics compared with controls (p less than 0.01), and correlated with blood glucose (r = -0.53, p less than 0.03) but not glycosylated haemoglobin at the time of testing. The difference in ischaemic index persisted even when baseline VPT measurements, rather than patients, were matched. Ischaemic index was re-tested in 15 patients after a median interval of 17 months (range 6-19), at which time mean +/- SD glycosylated haemoglobin had improved significantly (12.2% +/- 0.4 versus 9.5% +/- 0.05, p less than 0.001), but this bore no relation to changes in ischaemic index. Peripheral nerve ischaemia-resistance is present at the time of diagnosis of non-insulin-dependent diabetes, even in the absence of other neurophysiological abnormalities, and is not explicable by glycaemic control alone.