Annular Erythema in a Nine-Year-Old Girl: A Rare Type of Psoriasis.

Annular erythema is a nonspecific clinical sign arising from various conditions, including infections, cutaneous lymphomas, connective tissue diseases, and inflammatory dermatoses. Psoriasis vulgaris typically presents as sharply demarcated erythematous plaques with silvery scales; however, annular forms are rare and may complicate diagnosis. We report a nine-year-old girl with an annular erythematous lesion on the anterior chest that gradually expanded over two months, spreading to the extremities and trunk with mild pruritus. Despite suspicion of tinea corporis, repeated fungal tests were negative, and topical corticosteroids were ineffective. Skin biopsy showed marked hyperkeratosis, loss of the granular layer with parakeratosis, and subcorneal Munro's microabscesses; no fungal elements were found. Laboratory tests and imaging were unremarkable, and genetic screening for IL36RN and CARD14 found no pathogenic variants. A diagnosis of psoriasis vulgaris was made with a Psoriasis Area and Severity Index (PASI) score of 7.8. After failed topical treatment, systemic secukinumab therapy was initiated, leading to complete lesion resolution within two months. This case emphasizes the importance of considering psoriasis in the differential diagnosis of pediatric annular erythema and demonstrates the value of histopathology and biologics in managing atypical pediatric psoriasis.