Near-infrared spectroscopic hand imaging: a new tool to assess microcirculatory impairment in systemic sclerosis

Background: Systemic sclerosis (SSc) causes functional and structural microcirculatory dysfunction, affecting also distal extremities. Optical Near-InfraRed Spectroscopy (NIRS) of blood HbO2 saturation (stO2) can evaluate microcirculation of the entire hand and its spatial heterogeneity. The NIRS-sensitive camera is a non-invasive tissue oxygenation measurement system, which reports value of stO2 in superficial tissue. The processing software automatically generates 2D imaging maps in real time. Objectives: Whether NIRS hand imaging may evaluate microcirculatory dysfunction in SSc compared to controls. Methods: Fifty-four SSc pts (age 55±16 yrs) and twenty-one healthy controls (mean age 51±14 yrs, p=.29) underwent evaluation of hand microcirculation by NIRS 2D imaging. A blood pressure cuff was applied to the forearm and 3-min ischaemia was induced. Images were acquired at basal conditions and each 10 secs during 3 mins of ischemia and during 5 mins of reperfusion. Five regions of interest were positioned on each fingertip, from the second to the fifth finger and one on thenar eminence. Results: A significant difference was found between controls and SSc in basal stO2 (84.3±7.5 vs 75.4±10.9%, p<.001), minimum stO2 (65.2±8.0 vs 53.4±10.1%, p<.001) and time to maximum stO2 (242±38 vs 265±49 msec, p<.05). Patients with Scl-70 antibodies had lower basal stO2 compared to pts without (69.3±12.7 vs 78.8±11.7, p<.05), as well as pts with diabetes mellitus (69.3±12.7 vs 78.8±11.7, p<.05). No significant differences were found among different degrees of impairment at nailfold capillaroscopy. Conclusions: NIRS hand imaging is a simple, automated promising tool to non-invasively assess the microcirculation of the entire hand, which can complement information deriving from nailfold capillaroscopy.