Background  Early stage mycosis fungoides (MF) is difficult to be clinically differentiated from chronic dermatitis (CD) in a high proportion of patients. Dermoscopy is a rapid, cheep, non-invasive and widely used method for the evaluation of skin tumours and, recently, of inflammatory skin diseases, as well.

Objective  To describe the dermoscopic pattern of early stage MF and compare it with the dermoscopic features observed in CD.

Methods  This was a retrospective study. Dermoscopic images of lesions that were clinically equivocal between MF and CD were evaluated for the presence of predefined morphologic criteria. Diagnosis had been histopathologically and immunohistochemically confirmed in all cases. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for predefined dermoscopic criteria in relation to the diagnosis of mycosis fungoides.

Results  A total of 67 dermoscopic images were selected for dermoscopic evaluation. Mycosis fungoides lesions exhibited a characteristic dermoscopic pattern consisting of fine short linear vessels (sensitivity 93.7%, specificity 97.1%) and orange-yellowish patchy areas (sensitivity 90.6%, specificity 99.7%). A characteristic vascular structure resembling spermatozoa was also found to be highly specific for the diagnosis of mycosis fungoides. CD was typified by a different dermoscopic pattern, usually consisting of dotted vessels.

Conclusions  These observations provide a first indication that early stage MF exhibits a characteristic dermoscopic pattern which is different from CD. Prospective studies with long term follow-up are needed to determine the value of these dermoscopic criteria in the differentiation between the two entities in the daily routine.