Sodium nitroprusside iontophoresis on the finger pad does not consistently increase skin blood flow in healthy controls and patients with systemic sclerosis.

OBJECTIVE: Sodium nitroprusside (SNP) iontophoresis is a commonly used technique to assess non endothelium-dependent skin microvascular function in the forearm. However, the lack of data on the finger pad is a limitation when studying diseases affecting the digits (e.g. systemic sclerosis, SSc). We thus aimed to validate this technique in the finger pad compared to the forearm in SSc patients and healthy controls.
METHODS: Six SSc patients and six controls were recruited. SNP and NaCl iontophoresis were performed on the finger pad and the forearm, with and without lidocaine/prilocaine. Cutaneous blood flow was simultaneously monitored using laser Doppler flowmetry.
RESULTS: In all subjects, iontophoresis of SNP induced hyperemia in the forearm, which was not affected by pretreatment with lidocaine/prilocaine. In contrast, no increase in cutaneous vascular conductance was observed in the finger pad in any subject (apart from one patient with SSc).
CONCLUSIONS: The iontophoresis of SNP leads to a consistent, non axon reflex-dependent, increase in cutaneous vascular conductance in the forearm, both in patients with SSc and in healthy controls. On the finger pad however, such hyperemia was not consistent. As a consequence, other tools should be considered to assess non endothelium-dependent skin microvascular function in the finger pad.