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Erythromelalgia (EM) is a chronic disorder characterized by intermittent burning pain, warmth and erythema of the extremities. Increasing the local temperature and dependency of the affected limb(s) precipitates the symptoms, whereas direct cooling and elevation of the limb(s) can provide partial relief. Our previous findings showed that patients with EM have enhanced cutaneous vascular tone at rest and during stimulation, which may be due to an increase in sympathetic neural activity. To test this, we measured skin vasoconstrictor responses to contralateral arm cold challenge (CC) and inspiratory gasp (IG) using laser Doppler flowmetry at the toe pulp and fingertip. These areas were chosen because of their dense sympathetic innervation. An index of the vasoconstrictor response (between 0 and 1) was calculated from the change in skin perfusion from baseline following CC and IG. In control subjects, vasoconstrictor responses to CC at the toe and fingertip were both 0. 70+/-0.02 (mean+/-S.E.M.), which were significantly greater (P<0. 001) than corresponding values in patients with EM (0.37+/-0.04 and 0.45+/-0.04 respectively). Similarly, vasoconstrictor responses to IG were significantly greater (P<0.001) at the toe and fingertip in control subjects (0.70+/-0.03 and 0.70+/-0.02 respectively) compared with values in EM patients (0.27+/-0.03 and 0.45+/-0.15 respectively). These data show that, in contrast with control subjects, patients with EM have diminished sympathetic vasoconstrictor responses to both CC and IG. Denervation supersensitivity may play a part by increasing vasoconstrictor responses to circulating catecholamines, leading to a reduction in skin blood flow. Therefore an interplay between neural and vasoactive agents may be involved in the pathophysiology of EM.

Objective: To assess the effects of oral L-arginine supplementation on cutaneous vascular responses in patients with primary Raynaud's phenomenon (RP)., Methods: Double-blind, crossover comparison of placebo versus L-arginine (8 gm/day for 28 days). Cutaneous vascular responses in the fingers were assessed during iontophoresis of acetylcholine and sodium nitroprusside, which are endothelium-dependent and endothelium-independent vasodilators., Results: In comparison with control subjects, patients with primary RP had diminished endothelium-dependent and -independent vasodilatation (P < 0.05, and P < 0.005, respectively, by analysis of variance). At the 3 doses used, vascular responses to acetylcholine were reduced by 71%, 64%, and 63%, respectively, and responses to sodium nitroprusside were reduced by 67%, 73%, and 66%, respectively. L-arginine had no significant effect on cutaneous vascular responses to acetylcholine or sodium nitroprusside in control subjects or patients with primary RP., Conclusion: Reduced vasodilator ability in primary RP is unlikely to be due to an impairment in the L-arginine/nitric oxide pathway.

Approximately 50% of the forearm vasodilatation to intra-arterial infusions of acetylcholine is mediated by endothelium-derived nitric oxide. These conclusions have been derived from venous occlusion plethysmographic measurements of total forearm blood flow during co-infusions of acetylcholine and NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthase. Since venous occlusion plethysmography measures total limb blood flow, the relative proportion of the measurement from skin cannot be determined precisely. To determine the effects of acetylcholine on skin specifically, we have used laser Doppler flowmetry to measure vascular responses to local iontophoresis of acetylcholine in the forearm of normal male volunteers. To elucidate the possible mechanisms of cutaneous vasodilatation to acetylcholine, vascular responses were measured before and after systemic inhibition of prostanoid production and nitric oxide synthesis by oral aspirin (600 mg daily for 3 days) and intravenous L-NMMA (3 mg/kg for 60 min), respectively. After aspirin administration, dose-dependent vascular responses to acetylcholine were reduced significantly by approximately 53% (p < 0.005, ANOVA). In contrast, intravenous L-NMMA appeared to have no significant effect on cutaneous vascular responses to acetylcholine. While the role of nitric oxide is uncertain, vasodilatation to acetylcholine in the forearm skin is mediated largely by a prostanoid-dependent mechanism. Assessment of cutaneous vascular responses to iontophoresis of acetylcholine may, therefore, be useful in diseases where abnormal endothelium-dependent prostanoid function has been implicated.