Signet Ring-Like Cells: A New Reflectance Confocal Microscopy Clue of Interface Dermatitis Correlated to Basal Cell Vacuolization in Histopathology

ized by a signet ring aspect. ‘RCM signet ring-like cells’ correspond to a complete annular bright ring with a polar reinforcement, surrounding a dark center. This aspect brings to mind the eccentric pyknotic nucleus encompassed by a vacuolized cytoplasm (appearing as a dark center) seen on the histopathological examination of a skin biopsy performed immediately after RCM on the very same area in 4 cases ( fig. 1 g, h, 2 c, f) – in 1 case, the biopsy had been performed before RCM ( fig. 1 i). We observed a higher number of signet ring-like cells with RCM images compared to the histopathological sections. This could be related to the en face horizontal view given by RCM. Keratinocyte necrosis and apoptotic keratinocytes are considered to be responsible for the vacuolar degeneration of the DEJ seen in interface dermatitis [4] . Intraepidermal necrotic keratinocytes have been described with RCM in lichen planus [2] and lupus erythematosus [3] as mildly bright, polygonal structures larger than surrounding keratinocytes. However, the cellular changes we observed at the DEJ, and which we correlated to basal cell vacuolization, have not been described in these previous pilot studies. We believe it is worth emphasizing this morphological alteration, which could represent an additional clue for the RCM diagnosis of interface dermatitis and which deserves to be confirmed by complementary studies.