Ostraceous Psoriasis Presenting as Koebner Phenomenon in a Tattoo.

Psoriasis is a common dermatologic condition with a variety of morphologic presentations. These variations include the less common hyperkeratotic form, psoriasis ostracea, defined as having pronounced adherent scales resembling an oyster shell. Of the ostraceous cases that have been reported in the literature, many occur as generalized outbreaks in patients with long-standing history of psoriasis. Rarely does this remarkable variant occur as a direct flare from a cutaneous insult. In these situations, when a pre-existing dermatosis appears in response to a traumatic insult to skin, the process is referred to as the Koebner phenomenon. In addition to lichen planus and vitiligo, psoriasis is a commonly known condition that can present as a Koebner reaction. In this atypical case, the authors present a 21-year-old male with remarkable ostraceous psoriatic lesions precipitated by an upper arm tattoo, demonstrating the Koebner phenomenon.