Differentiation of pityriasis rubra pilaris from plaque psoriasis by dermoscopy

Pityriasis rubra pilaris (PRP) and plaque psoriasis (PP) are two distinctive erythemato-squamous skin diseases that often have to be differentiated from each other and from other similar dermatoses. Dermoscopy has been proven to aid the clinical diagnosis of several inflammatory disorders, minimizing the need for skin biopsy. Our aim was to determine the dermoscopic patterns of PRP compared to PP and to assess the significance of certain dermoscopic criteria in the diagnosis of PRP. This case-control study included 11 patients with biopsy proven PRP and 25 patients with biopsy proven plaque psoriasis. The most recently developed lesion of each patient was examined by non-contact dermoscopy. Whitish keratotic plugs and linear vessels in yellowish background are significant dermoscopic features of PRP compared to white diffuse scales and dotted vessels in a light red background in PP. In conclusion, PRP and PP reveal specific distinguishing dermoscopic patterns that may assist in their clinical diagnosis and may also be useful for the differential diagnosis from other resembling dermatoses.