S. K. T. Que, N. Fraga-Braghiroli, J. M. Grant-Kels, H. S. Rabinovitz, M. Oliviero, and A. Scope, “A pink papule on the back of an 82-year-old man: an example of the buttonhole sign on reflectance confocal microscopy”, Dermatol Pract Concept, pp. 1–2, Jul. 2016, doi: 10.5826/dpc.0603a01.