Diagnostic accuracy of hyperpigmented microcircles in dermatoscopy of non-facial non-acral melanomas. A pilot retrospective study using a public image database.

Background: Grey perifollicular circles are a dermatoscopic clue to melanoma, especially in facial skin. So far, no other adnexal clues than follicular have been investigated in this diagnosis.Objectives: The study aimed to analyse the prevalence of hyperpigmented periadnexal microcircles (HM) in melanoma and its common simulators at non-facial non-acral sites, analyse the relation between the presence of MH, regression and hypopigmentation, and evaluate the diagnostic accuracy of this structure in melanoma.Methods: International Skin Imaging Collaboration (69445 images), was searched in April 2020 for the pathology-confirmed dermatoscopic images with metadata including sex, age bin, and declared non-acral non-facial anatomic site. The final study sample (5408 images, 1326 of which were melanomas) was evaluated by expert dermatoscopist blinded to the diagnosis and labelled for the presence of & GE;3 HM distributed centrally (cHM) or peripherally (pHM), hypopigmentation and classic dermatoscopic regression structures. A subset of 40 images were labelled by 7 raters (2 residents, 5 experts) to assess interobserver agreement. We compared the presence of pHM with the presence of regression as well as performed a set of independent Chi-squared tests to evaluate the discriminatory power and its fragility. Performance of the models was assessed using measures of discrimination and calibration.Results: HM were significantly more prevalent in melanomas than in non-melanomas and nevi. Fair/good interobserver agreement for HM was reached for all the raters, and moderate/good for experts only (single rater/average, respectively). Regardless of regression/hypopigmentation status, pHM were significantly more common in melanoma than in non-melanomas or nevi, and were observed significantly more often in melanomas on sun damaged skin (upper extremity, posterior torso). No significant differences between the groups were found for cHM. pHM proved a high odds ratio in the tests as to the classical indicators such as classic dermatoscopic regression structures.Conclusion: pHM could be considered a novel dermatoscopic clue to melanoma.