Reliability of dermoscopy in the assessment of patients with Raynaud's phenomenon

Few rheumatologists have access to wide field or video capillaroscopy (abnormal capillaries being highly predictive of CTD), and a key question is whether they should, therefore, purchase a dermatoscope. The aim of this study was to estimate the inter- and intra-observer variability of dermoscopy (magnification 10x) among rheumatologists with little or no experience of the technique. Good reliability is a necessary prerequisite for a test to be a valid clinical or research tool.

Dermoscopy was performed in all 10 nail folds from 16 subjects with a range of capillary normality/abnormality. The 160 nail fold images thus acquired were made into two PowerPoint presentations, each of 80 images with 16 duplicate slides. Each participating rheumatologist graded one of the sets of 96 images, grading scale (0-3): normal, mildly abnormal/'suspicious', definitely abnormal, grossly abnormal capillaries or 'unclassifiable' when capillaries could not be adequately identified. Data from both presentations were pooled for analysis.

Twenty-eight rheumatologists participated in the study. For the decision as to whether an image could be classified or not, the inter- and intra-observer kappa-coefficients were 0.59 (95% CI 0.51, 0.67) and 0.63 (95% CI 0.45, 0.74), respectively. Conditional on being able to classify, the intra-class correlation coefficient for inter- and intra-observer reliability was 0.72 (95% CI 0.66, 0.77) and 0.85 (95% CI 0.82, 0.92), respectively.

Inter- and intra-observer reliability were good, suggesting that with little training, dermoscopy is likely to be a useful technique to identify capillary distortions/underlying CTD.