Capillaroscopy has gained traction in rheumatology for its known correlation to systemic sclerosis and dermatomyositis, which have considerable microvasculature change. In the setting of systemic sclerosis, capillaroscopy abnormalities have a distinct enough phenotype to help aid in diagnosis. Endovascular dysfunction is felt to occur early in the disease with a reduction in nitric oxide, increased cell adhesion molecules for inflammatory cell chemotaxis, and eventually a fibroproliferative process (20). In dermatomyositis, a different capillary pattern is seen with neoangiogenic change (eg, bushy capillaries, loss of architecture). The microvascular change is felt to be immune mediated, perhaps due to increased type 1 interferon and complement deposition (21). Interestingly, capillaroscopy changes are reversible with therapy in dermatomyositis, indicating it could potentially be used to monitor disease activity (16).
AAV is a group of illnesses characterized by inflammation of the capillary beds that preferentially affect the skin through vascular rashes, lungs through diffuse alveolar hemorrhage, and kidneys through glomerulonephritis. Studies have shown that this is a pauci-immune process without immunoglobulin or complement deposition. There is a loss of tolerance that allows for antibody development to myeloperoxidase and proteinase 3. These ANCA then stimulate neutrophils to further the inflammatory environment within the capillary beds (22). Given the multiorgan microvascular inflammation that occurs in these conditions, our study aimed to assess for capillary changes in the nailfold using capillaroscopy, a widely accessible clinical tool.
A recent publication by Matsuda et al (23) compared 51 patients with AAV with healthy controls. They reported AAV had statistically relevant changes in all components of the capillaroscopic examination, which is in contrast to our own findings. Several phenotypes were described, including a microangiopathic pattern (70.6%), scleroderma pattern (7.8%), and normal examination (21.6%). All patients in their cohort with AAV had active disease and were hospitalized, which is a notable difference from our own cohort which was enrolled from clinic. It is possible that these findings correlate more with severe disease, and their article did suggest improvement in the NVC findings posttreatment (23). Another consideration would be that the critically ill or hospitalized patient may be more likely to have nonspecific capillaroscopy findings such as microhemorrhage due to other contributing factors (eg, hypercoagulability due to critical illness, low dose heparin for deep vein thrombosis prevention, microvascular change from hypertension and hyperglycemia). This could be addressed with additional studies accounting for the confounding data that having an outpatient control and inpatient disease cohort could introduce.
Frequent capillary abnormalities have been reported, usually at low levels, in the general population (24). Similarly, our control group had some higher scores than expected; 1 patient with capillary dilation and 2 with frequent microhemorrhages. Known patient history may explain some abnormality (eg, 1 patient with multiple microhemorrhages cleans houses with repeated scrubbing using the nails); however, unknown variables may have also altered the examinations. Other illnesses that affect the vasculature have been noted to cause change on capillaroscopy, including diabetes mellitus and dialysis dependence. Bleeding disorders and recent trauma to the nailfold can also result in abnormal findings. Overall, this highlights that mild capillary abnormalities can be seen in typical patient populations and are not exclusive to rheumatic disease.
Our study has several limitations. There was a lack of blinding for the capillaroscopy procedure; however, this would have been expected to skew the results to overestimate differences. Furthermore, while all patients in the AAV group had a diagnosis of AAV, some were in clinical remission at the time of review and only 1 in 5 had experienced a recent flare. Ideally, the study would have included new incidental cases with active disease. However, we do note that abnormalities were minimal even in patients with recent disease activity. For practical clinical use, we feel that patients would have to have widely prevalent nailfold capillary change or at least a strong phenotype with active disease; however, neither of these criteria were met. The significant prevalence of abnormal capillaroscopy findings and specific phenotype are the reasons capillaroscopy has been found to be useful in dermatomyositis and systemic sclerosis. Further studies are still needed to clarify whether there are meaningful subgroups withing these vasculitides that would benefit from capillaroscopy.