Ostraceous Psoriasis, An Unusual Presentation: Case Report

We report the case of a 16 year old female patient, Fitzpatrick skin phototype IV, who presented with a generalized, bilateral, and symmetrical dermatosis characterized by erythematous plaques of oval configuration with well defined regular borders. The lesions exhibited whitish, hyperkeratotic, concave scales resembling oyster shells on their surface, with variable distribution and size, pruritic in nature, and of two months’ evolution. Histopathological examination was consistent with psoriasis vulgaris. Systemic therapy with methotrexate was initiated, combined with high potency topical corticosteroids (clobetasol cream 0.05%), achieving satisfactory clinical improvement after three months of treatment. Ostraceous psoriasis is an uncommon presentation, with few cases reported in the literature. It accounts for approximately 26% of the atypical hyperkeratotic variants of plaque psoriasis. The diagnostic hallmark lies in the recognition of the elementary lesion: plaques with an erythematous ring and infiltrated base, circular in configuration, with regular and well defined borders, and an internal concave, concentric, and conical surface that imparts the characteristic oyster shell appearance. Therapeutic management is generally based on conventional systemic and topical regimens; however, in refractory cases, biological therapy has been employed with favorable outcomes.