Histopathological differential diagnosis of nail psoriasis and onychomycosis

About 160 million in the world are suffering from psoriasis, which is thus one of the most prevalent inflammatory skin diseases. It has a genetic background with very strong environmental influence. The clinical pictures are extremely variable, and it may be justified to assume that almost every psoriasis patient has his own form. Psoriasis may be a minor problem or life-threatening. Particular localizations have a serious impact on the patients’ life. Nails are frequently affected and present with very different alterations that depend on the nail structures involved. Onychomycoses are a group of nail infections and said to be the most frequent nail diseases. The way of fungal invasion determines the clinical and histopathological characteristics. Both conditions have many features in common rendering the differential diagnosis difficult. To make it even more complicated both nail psoriasis and onychomycosis may occur in the same patient, sometimes affecting different nails, more often involving the same nails. This review describes the histopathology of these frequent nail conditions and how to differentiate them.