Nailfold Capillaroscopy Analysis Can Add a New Perspective to Biomarker Research in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

Background: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA), all of which are characterised by inflammation of small-medium-sized vessels. Progressive understanding of these diseases has allowed researchers and clinicians to start discussing nailfold video capillaroscopy (NVC) as a future tool for many applications in daily practice. Today, NVC plays a well-established and validated role in differentiating primary from secondary Raynaud's phenomenon correlated with scleroderma. Nevertheless, there has not been sufficient attention paid to its real potential in the ANCA-associated vasculitis. In fact, the role of NVC in vasculitis has never been defined and studied in a multicentre and multinational study. In this review, we carried out a literature analysis to identify and synthesise the possible role of capillaroscopy for patients with ANCA-associated vasculitis. Methods: Critical research was performed in the electronic archive (PUBMED, UpToDate, Google Scholar, ResearchGate), supplemented with manual research. We searched in these databases for articles published until November 2023. The following search words were searched in the databases in all possible combinations: capillaroscopy, video capillaroscopy, nailfold-video capillaroscopy, ANCA-associated vasculitis, vasculitis, granulomatosis with polyangiitis, EGPA, and microscopic polyangiitis. Results: The search identified 102 unique search results. After the evaluation, eight articles were selected for further study. The literature reported that capillaroscopy investigations documented non-specific abnormalities in 70-80% of AAV patients. Several patients showed neoangiogenesis, capillary loss, microhaemorrhages, and bushy and enlarged capillaries as the most frequent findings. Furthermore, the difference between active phase and non-active phase in AAV patients was clearly discernible. The non-active phase showed similar rates of capillaroscopy alterations compared to the healthy subjects, but the active phase had higher rates in almost all common abnormalities instead. Conclusions: Microvascular nailfold changes, observed in patients affected by vasculitis, may correlate with the outcome of these patients. However, these non-specific abnormalities may help in the diagnosis of vasculitis. As such, new analysis analyses are necessary to confirm our results.