Abnormal digital neurovascular response to local heating in systemic sclerosis

Objectives. To investigate neurovascular dysfunction using the axon reflex-dependent hyperaemia (initial peak of skin local heating response) in fingers of patients with SSc or primary RP. Methods. Ten healthy subjects were initially enrolled to compare axon reflex-dependent thermal hyperaemia between the finger and forearm cutaneous circulations. Then, 10 patients with primary RP and 16 patients with SSc participated in a similar protocol focusing on the finger circulation only. Lidocaine/prilocaine cream was applied for 1 h to produce local blockade of cutaneous sensory nerves. After lidocaine/prilocaine pre-treatment, laser Doppler probes were heated from skin temperature to 42 degrees C for 30 min, and 44 degrees C for 5 min to achieve maximal skin blood flow. Data were expressed as a percentage of maximal cutaneous vascular conductance. Results. In healthy volunteers, we observed a significantly higher initial peak on the finger compared with the forearm, with both responses blunted following topical anaesthesia. In primary RP patients, we observed a decreased initial peak following lidocaine/prilocaine pretreatment in the finger circulation [96.7% (33.4) vs 75.9% (29.5) with anaesthesia, P=0.02]. In contrast, pre-treatment did not alter the initial peak in patients with SSc. A minute-by-minute analysis showed no delay of the initial peak. Conclusions. We show an abnormal digital neurovascular response to local heating in SSc. Thermal hyperaemia could be monitored as a clinical test for neurovascular function in SSc. Further studies are required to test whether the abnormal digital neurovascular response correlates to the degree of peripheral vascular involvement.