ORIGINAL ARTICLE In vivo confocal microscopic substrate of grey colour in melanosis E. Cinotti, 1, * C. Couzan, 1 J.L. Perrot, 1 C. Habougit, 2 B. Labeille, 1 F. Cambazard, 1 E. Moscarella, 3 A. Kyrgidis, 3 G. Argenziano, 3 G. Pellacani, 4 C. Longo 3 1 Department of Dermatology, University Hospital of Saint Etienne, Saint Etienne, France 2 Department of Pathology, University Hospital of Saint Etienne, Saint Etienne, France 3 Skin Cancer Unit, Arcispedale S. Maria Nuova-IRCCS, Reggio Emilia, Italy 4 Department of Dermatology, University of Modena and Reggio Emilia, Modena, Italy *Correspondence: E. Cinotti. E-mail: elisacinotti@gmail.com Abstract Background Melanosis is the most common cause of mucosal pigmentation and can be clinically difficult to differentiate from early melanoma (MM). Dermoscopy can help in the distinction between melanosis and MM, but in some instances, melanoses may exhibit overlapping features with MM such as the presence of grey colour. Objective We sought to evaluate whether reflectance confocal microscopy (RCM) can help to better understand the dermoscopic features of melanoses in order to assist clinicians in their diagnosis. Methods All melanoses diagnosed between June 2011 and December 2014 in the Departments of Dermatology of the University of Saint-Etienne (France) and of Modena and Reggio Emilia (Italy), for which dermoscopic and RCM images were available, were included. Twenty-two lesions were biopsied to confirm the clinical diagnosis, whereas the others did not present any change at a follow-up of at least 6 months. The correlation between dermoscopic and RCM features were evaluated by the Spearman’s rho correlation coefficient. Results 55 melanoses were studied: 31 of the oral mucosa and 24 of the genital mucosa. 49% (n = 27) of melanoses exhibited a grey colour under dermoscopy. The grey colour correlated with the presence of melanophages under RCM (q = 0.424, P = 0.002). Conclusion Our findings highlight that the presence of the grey colour on dermoscopy, considered as an alerting fea- ture, is common in melanoses and it is related to the presence of melanin-laden inflammatory cells in the papillary dermis on RCM. When it is present as a ‘pure’ feature not associated to other colours than brown or to atypical dermoscopical structures, it could be related to the diagnosis of melanosis. Received: 3 June 2015; Accepted: 27 July 2015 Conflict of interest The authors declare no conflicts of interest to disclose. Funding sources Dr Cinotti was supported by the grant ‘bourse d’aide  a la mobilit e’ from the College des Enseignants de Dermatologie de France CEDEF. Introduction Melanosis, also called melanotic macule and mucosal-pigmented macule, is a benign pigmentation of the mucosa, corresponding to hyperpigmentation of basal keratinocytes with possible slight proliferation of melanocytes at the epithelial-chorion junction (ECJ). It is the most common cause of mucosal pigmentation and can be clinically difficult to differentiate from early mela- noma (MM), especially when occurring on genitalia. 1–3 In fact, in this special body site, melanosis can reveal worrisome clinical features, as multiple, asymmetric macules or patches with variable colour and irregular and poorly demarcated borders. 3 To further complicate the matter, early mucosal MM can present as brown macule thus simulating a benign pigmentation which can lead to a misdiagnosis. 4 A correct differential diagnosis between melanosis and MM is crucial to avoid unnecessary biopsies of the mucosa which is a sensitive tissue, and to avoid a delay in the diagnosis of mucosal MM. In fact, mucosal MM is often diagnosed too late with related poor prognosis, whereas its early identification and inter- vention could improve patient outcomes. 3 © 2015 European Academy of Dermatology and Venereology JEADV 2015, 29, 2458–2462 DOI: 10.1111/jdv.13394 JEADV