Supplementary Material for: The importance of histopathology in the diagnosis of Annular Lichenoid Dermatitis of Youth: A case report

Introduction: Annular lichenoid dermatitis of youth (ALDY) is a rare and underreported dermatologic condition. It primarily affects children and adolescents. Clinically, ALDY presents as erythematous annular macules or plaques with raised borders and hypopigmented centers, predominantly affecting the trunk and flexural areas. The etiology remains unknown, and the condition poses a diagnostic challenge due to its resemblance to other annular dermatoses. Case Presentation: A 5-year-old female presented with asymptomatic annular erythematous lesions on the trunk, abdomen, lumbar region, and flanks. Initial differential diagnoses included annular erythema, tinea corporis, morphea, and mycosis fungoides. A mycological examination was negative, and symptomatic treatment with hydrocortisone and pimecrolimus led to temporary lesion resolution, but recurrence followed treatment cessation. A skin biopsy revealed histopathological features characteristic of ALDY, including basal layer vacuolization and a prominent lichenoid lymphocytic infiltrate. Immunohistochemical analysis supported the diagnosis. Conclusion: ALDY remains a diagnostic challenge due to its clinical overlap with other annular dermatoses. Histopathological examination is essential for definitive diagnosis. The chronic and recurrent nature of ALDY underscores the importance of long-term management strategies, including topical corticosteroids and immunomodulators. Awareness of ALDY among dermatologists can aid in early recognition and appropriate management, ultimately improving patient outcomes.