Background Nailfold capillaroscopy is an imaging technique used for the in vivo assessment of the microcirculation that has been receiving increasingly attention as a potential prognostic tool in patients with connective tissue diseases. Although successfully applied since many years, very few data has been published about prevalence and distribution of capillary changes in healthy individuals.

Objectives To identify different profiles of nailfold capillary characteristics within capillaroscopic pattern in healthy subjects.

Methods We studied nailfold capillaroscopy of 100 healthy volunteers recruited in two Rheumatology centers by evaluating the number of capillaries, morphologic aspects (i.e. U shaped, tortuous, crossed, bushy or meandering loops), microhemorrhages, intercapillary distances, loop length, capillary width. The forth and the fifth finger of both hands were examined. Videocapillaroscopy was performed using a videocapillaroscope equipped with a 200x optical probe, with the images (a mean of 4 images/patient) being captured, coded, and stored using Videocap software (DS-Medica, Milan, Italy). The inter-observer agreement was evaluated by the weighted Cohen’s kappa (WCK) for categorical variables and by the Intraclass Correlation Index (ICC) for the continuous ones. The profiles were identified by cluster analysis.

Results Nailfold capillary images of 99 of 100 subjects were evaluated. A total of 400 nailfold images were analyzed. Since the distributions of the capillary parameters appear quite similar among the four fingers, the subsequent analysis will use the data of the fourth finger of right hand. There is a good inter-observer agreement about both the categorical and continuous variables (all WCK’s are greater than 0.80 while all ICC greater than 0.67).Based on the capillary length and number, two clusters have been identified. They are mainly characterized by: cluster A (82 subjects) with internal loop diameter <15 μm, or internal diameter ≥15 μm and capillary number <8 /mm; cluster B (17 subjects) with internal loop diameter ≥15 μm and capillary number ≥8/mm.According to the frequency of the capillary morphologic aspects, six clusters were obtained. These are mainly described by means of the following patterns: cluster 1 (21 subjects) with U shaped loops between 5 and 9/mm; cluster 2 (71 subjects) with U shaped loops (between 1 and 5/mm) and tortuous loops (<2/mm); cluster 3 (2 subjects) with meandering loops; cluster 4 (2 subjects) with twisted loops (between 2 and 6/mm); cluster 5 (2 subjects) with microhemorrhages; cluster 6 (1 subjects) with bushy loops. The last four clusters are represented by a low number of peculiar subjects which are very heterogeneous. There is a significant association between the two clusterings (Fisher test: p=0.01). In cluster A are grouped the majority of subjects of the cluster 1, 2 and 3, while cluster B contains mainly subjects of cluster 2. Concerning the clusters from 3 to 6, there is not a clear separation between clusters A and B.

Conclusions This study highlights that there is a wide range of capillary parameters characterizing the nailfold capillaroscopy findings in healthy subjects. This is a fundamental starting point to understand the range of normality so that microangiopathy can be identified or ruled out.

Disclosure of Interest None Declared