R. Barabash-Neila, L. Rodríguez-Fernández Freire, T. Zulueta-Dorado, and J. Conejo-Mir, “Thickening of the Skin on the Forehead: A Quiz”, Acta Derm Venereol, vol. 91, no. 1, pp. 108–111, Jun. 2010.