Intraoperative dermoscopic features of onychomatricoma: a review of 10 cases

Summary Background Amelanotic nail tumours are difficult to diagnose. Dermoscopy is an accessible tool successfully used in diagnosis of amelanotic or melanotic skin tumours. We have previously shown the usefulness of dermoscopy in the preoperative diagnosis of onychomatricoma (OM). In this study, we completed this work by identifying additional intraoperative criteria to better establish the initial diagnosis of this tumour. Aims Evaluation of intraoperative dermoscopy in a small series of OM cases in order to define relevant diagnostic criteria. Methods In total, 10 patients with OM diagnosed in our centre were enrolled in the study. Six trained dermoscopists individually evaluated each criterion, then the data were compared and a consensus reached after discussion between the observers. For each criterion, we analysed its frequency and its interobserver accordance. We defined three architectural criteria (the ‘Sagrada Familia’ sign, digitations and the ‘mirror sign’), and three vascular criteria (sagittal vessels, dotted vessels and irregular vessels). Results The Sagrada Familia sign, digitations and mirror sign were found in 100%, 90% and 70% of the cases, respectively, with high interobserver agreement. The vascular criteria were less regularly observed: sagittal, dotted and irregular vessels were respectively found in 80%, 70% and 50% of the OM cases, and were more difficult to assess, as shown by the lower interobserver agreement rates. Conclusion Intraoperative dermoscopy of the nail matrix and bed offers useful information for the diagnosis and management of OM. Larger comparative studies should be performed to evaluate the true benefit of this approach.