Mimicry illuminating pitfalls in histopathologic diagnosis: nutritional deficiency-like dermatitis secondary to topical tazarotene and keratoacanthomatous pseudocarcinomatous hyperplasia in CD30+ lymphoproliferative disorder as illustrative.

In the course of daily sign-out, histopathologists are confronted with instances in which the histopathologic findings may simulate another entity. At times, it can be extraordinarily difficult to distinguish the simulacra from the authentic. Sometimes this happens because different conditions rarely may show nearly identical histopathologic findings. Other times the most prominent histopathologic findings are not the diagnostic ones, yet they may closely resemble a specific entity that is wholly unrelated to the diagnosis. An example of each of these types of mimicry is presented in conjunction with a discussion of the associated pitfalls in diagnosis. Last, a brief discussion of different categories of histopathologic mimicry is presented.