A new minimally invasive technique to show nerve ischaemia in diabetic neuropathy

Aims/hypothesis. Experimental studies have shown that abnormalities of nerv e microcirculation are important factors in the pathogenesis of diabetic ne uropathy but there have been few clinical studies. We have applied microlig htguide spectrophotometry to measure intravascular oxygen saturation (HbO(2 )%) and blood flow in human sural nerve. Methods. We studied ten patients with mild-moderate sensory motor diabetic neuropathy, nine patients without neuropathy and nine control subjects. We took 300 measurements of oxygen saturation under direct visual control thro ugh a 1.9 mm rigid endoscope over three regions of the nerve. Spectrophotom etric measurements of nerve fluorescence were taken after an intravenous in jection of sodium fluorescein and the rate of increase in nerve fluorescenc e (rise time) was used as an indicator of nerve blood flow. Results. Nerve oxygen saturation was reduced in patients with neuropathy co mpared with control subjects (67.1 +/- 2.2 % vs 76.7 +/- 2.1 %, p = 0.006). Fluorescein rise time was prolonged in patients with neuropathy compared w ith the control group (48.5 +/- 7.0 s vs 14.0 +/- 3.1 s, p = 0.001) suggest ing impaired nerve blood flow. There was a correlation between rise time, n erve oxygen saturation, glycaemic control and sural nerve sensory conductio n velocity (p < 0.01). Conclusion/interpretation. The combination of microlight-guide spectrophoto metry and micro-endoscopy provides a valuable minimally invasive technique for clinical investigation of nerve microcirculation. We have shown reduced nerve oxygenation and impaired blood flow in diabetic neuropathy and these findings strongly support a central role of microvascular disease in the p athogenesis of diabetic neuropathy.