Perianal Psoriasis as the First Manifestation of the Disease

Abstract Introduction  Inverse psoriasis affects the skin of flexural areas, such as the groin, axillae, umbilicus, intergluteal fold, and external genitalia. Clinical Case  We herein report the case of a man who presented with anal pruritus and, upon physical examination, a perianal dermatosis was found, which was characterized by erythematous plaques, with fine scaling. The case was initially managed with zinc oxide, and when no improvement was observed, we decided to take an incisional biopsy, which indicated histological changes suggestive of psoriasiform dermatitis. Discussion  Inverse psoriasis affects 3% to 7% of patients with psoriasis, and it manifests with erythematous plaques without the classic scaling appearance. The skin in these areas is susceptible to maceration, irritation, and ulceration, which alter the classic clinical picture. It may present with typical lesions or, less frequently, in isolation in the anogenital region. In the anogenital presentation only, the diagnosis should be made by biopsy, looking for the classic histopathological features of psoriasis. As for the first-line treatment, low- or medium-potency topical steroids are used for short periods of time; the second-line treatment is with emollients and tar-based products; and the third-line treatment uses an immunomodulator. Conclusion  This presentation is infrequent, and it requires a high index of suspicion for the diagnosis, always supported by biopsies, in search of the classic histopathological features of psoriasis.