1. To investigate the nature of sympathetic dysfunction in the pathogenesis of reflex sympathetic dystrophy, the microcirculatory vasoconstrictive responses to dependency were investigated in the skin of the hand of 76 reflex sympathetic dystrophy patients with unilateral disease by means of laser Doppler flowmetry (in perfusion units) and capillary microscopy. The patients were divided into three stages according to their perception of skin temperature (stage I in the case of a stationary warmth sensation, stage II in the case of an intermittent warmth and cold sensation, and stage III in the case of a stationary cold sensation). The vasoconstrictive responses were induced by lowering of the affected hand.

2. As compared to controls, the mainly sympathetically mediated vasoconstrictive response at thermoregulatory level of the skin microcirculation, as measured by laser Doppler flowmetry, was attenuated at stage I (1.82 versus 1.41, P < 0.05), stage II (1.82 versus 1.09, P < 0.0001) and stage III (1.82 versus 1.14, P < 0.01), suggesting the involvement of sympathetic denervation at all stages of the reflex sympathetic dystrophy syndrome. This sympathetic denervation may also account for the observed increase in thermoregulatory skin blood flow at stage I as compared to controls (152 versus 81, P < 0.01).

3. Since sympathetic denervation has been reported to cause increased sensitivity of vascular structures to catecholamines, the decrease in thermoregulatory skin blood flow at stages II (54 versus 81, P < 0.05) and III (31 versus 81, P < 0.05), both as compared to controls, may result from hypersensitivity to catecholamines of skin microvessels.

4. The sympathetically independent vasoconstrictive response at the nutritive level of skin microcirculation, as measured by capillary microscopy, was impaired only at stage III as compared to controls (1.04 versus 2.06, P < 0.05). This divergence in microvascular reactivity upon dependency of the nutritive and thermoregulatory subsystems also supports the hypothesis of sympathetic dysfunction.

5. The disturbed vasoconstrictive responses to dependency may give rise to raised capillary pressures, contributing to the formation of oedema.

6. These findings suggest that sympathetic denervation and consequent hypersensitivity to catecholamines play an important role in the pathophysiology of reflex sympathetic dystrophy.

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