Abnormal vasoreaction to arousal stimuli - An early sign of diabetic sympathetic neuropathy demonstrated by laser Doppler flowmetry

Early diagnosis of diabetic autonomic neuropathy contributes to the prevention of serious complications and improves the prognosis of patients with diabetes. Common tests of peripheral autonomic function are the quantitative sudomotor axon reflex test or the sympathetic skin response (SSR). Quantitative sudomotor axon reflex test is quantifiable but technically demanding. Sympathetic skin response cannot be quantified easily. To study whether measurement of skin vasomotion is suited to assess early sympathetic peripheral neuropathy, we monitored skin blood flow at the index finger pulp using laser Doppler flowmetry before and after electrical stimulation. We assured that the stimulus was sufficient to elicit an efferent sympathetic response by monitoring palmar SSR ipsilateral to the flow measurement. In 21 diabetic patients with at least stage one polyneuropathy and 21 age-matched controls, SSR was recorded from one palm and sole following electrical stimulation at the contralateral wrist. Sympathetic skin response was present at the palms in all patients and controls and absent at the sole of two patients only. Eight patients (38.9%) had abnormal SSR, with absent plantar responses in two patients, prolonged plantar latencies in six patients, and prolonged volar SSR latencies in two patients. Skin blood flow responses were more often abnormal (46.1%) than SSR (P < 0.05), responses were delayed in two patients and absent in another 8 patients. Skin blood flow retest reliability was high with a repeatability coefficient of 10.64% in controls and 12.34% in patients. Skin blood flow monitoring after sympathetic stimulation provides a reproducible parameter of sympathetic vasomotor control and complements the diagnostic value of SSR testing.