[Methodology and clinical use of superb microvascular imaging in assessing micro-circulation changes of fingertips in systemic sclerosis].

OBJECTIVE: To explore the feasibility of superb microvascular imaging (SMI) in evaluating microcirculation damage of the finger of systemic sclerosis (SSc), and determining the optimal scanning method by assessing the effect of scanning position (finger pulp or nail bed), plane (transverse or sagittal) and Doppler gain on the results. METHODS: In the study, 32 SSc patients and 32 non-SSc volunteers admitted to Peking University Third Hospital from February to October 2022 were included. The SMI image under different gain set (40 dB or 35 dB) of the third fingertip (sagittal scans or transverse scan of nail bed or pulp) of both hands were collected while vascular index (VI) was measured. RESULTS: Non-SSc volunteer presented abundant SMI signal distributed in the third fingertip. Arteriole of nail bed was observed on the dorsal side of the distal phalanx under SMI and gave off multiple vertical branches towards the nail. The arteriole of finger pulp ran parallel to the skin and gave off vertical branches towards the skin distributing subcutaneously as a network. In SSc group, the SMI signal in nail bed and finger pulp was reduced. The arteriole of nail bed and finger pulp was discontinuous and presented as sporadic dots and short rod-like color signal under SMI. The vascular index of the SSc patients was significantly lower than that of the non-SSc controls (P < 0.001). Among different positions and sections, the area under the receiver operating characteristic curve (AUC) of the sagittal plane of nail bed was the highest. Under low gain, the AUC of sagittal plane of nail bed was 0.871, the cut-off value was 5.4%, the sensitivity was 90.6%, and the specificity was 74.2%. Under high gain, the AUC was 0.893, the cut-off value was 14.0%, the sensitivity was 75.0%, and the specificity was 93.6%. Multivariate analysis showed that there was statistical significance on the diagnostic impact of the sagittal plane of nail bed (P < 0.005 for high gain condition; P < 0.05 for low gain condition). CONCLUSION: SMI can be used to evaluate the abnormal changes of vascular in patients with SSc. Using the sagittal scan of nail bed with high gain can evaluate the vascular loss of the fingertip in SSc patient accurately and specifically.