Nailfold capillaroscopy as diagnostic test in patients with psoriasis and psoriatic arthritis: A systematic review.

Up to 30 % of patients with psoriasis (PsO) develop psoriatic arthritis (PsA), and diagnosis can be difficult. Nailfold capillaroscopy (NC) is an easily applicable, non-invasive procedure to assess skin microcirculation. This systematic review investigates NC as diagnostic tool for PsO and PsA, including correlations between NC outcome measures to clinical and laboratory outcome measures. This systematic review was built on the PICO and PRISMA guidelines. In total 22 relevant studies were found Searching in the Web of Science, PubMed and Embase, latest update June 13th, 2022. The following NC outcome measures are found to be significantly more prevalent in PsO patients than healthy controls: reduced density, reduced length and more abnormal morphology. Likewise, in PsA patients, reduced density, more abnormal morphology, more microhaemorrhages and fewer hairpin shapes are found to be significantly more prevalent. Results were non-conclusive in terms of disease activity and duration with NC findings. Random-effects meta-analysis showed a significant reduction of density in PsO patients compared to healthy controls (studies: 6, n = 249; SMD = -0.91; 95 % CI [-1.41, -0.40], p = 0.0058, heterogeneity I2=74 %, AUC = 0.740) and in PsA patients compared to healthy controls (studies: 5, n = 130; SMD = -1.22; 95 % CI [-2.38, -0.06], p = 0.0432, heterogeneity I2=89 %, AUC = 0.806). No NC outcome measures were overall conclusive in differentiating PsO from PsA. Considering the conflicting results and small sample sizes further large-scale research on the identification of capillaroscopic changes in PsO and PsA and correlations with standardised clinical and laboratory outcome measures are necessary.