The role of reflectance confocal microscopy in the diagnosis of eccrine poroma: A retrospective case-control study

Eccrine poroma (EP) is a rare benign adnexal tumor that may mimic benign or malignant tumors and differential diagnosis may be difficult under clinical and dermoscopic examination. Reflectance confocal microscopy (RCM) examination may add important information to diagnosis and subsequent management of solitary lesions for which dermoscopy can be challenging. The aim of the present study was to investigate features of EP at RCM in order to detect the characteristics that might aid in the differential diagnosis of EP versus other solitary lesions (benign or malignant). Secondary objective was to correlate the resulting features with histopathological findings. This monocentric retrospective observational case-control study included all EPs registered with RCM between January 2007 and May 2018. Control cases were benign or malignant lesions similar in clinical appearance, morphology, and dermoscopic features to EPs. RCM evaluators were blinded to clinical-dermoscopic images and to final histopathological diagnoses. Finally, RCM-histopathological correlation was performed. A total of 11 EPs and 33 controls were included in the present study. Among RCM parameters, "cords without palisading," "dark holes," "prominent vascularization" and "abundant stroma" resulted positively associated with EP in univariate analysis. RCM features correspond to the histopathological diagnosis of EP in 97% of cases, as illustrated by the cluster analysis. An excellent correlation between diagnostic features of conventional histopathology and RCM was observed. RCM assists in the differential diagnosis of solitary lesions, allowing to reach a correct diagnosis of EP through the identification of its four characteristics.