Cutaneous manifestations associated with adult-onset Still's disease: important diagnostic values
Adult-onset Still's disease (AOSD) is a systemic inflammatory condition, characterized by a high spiking fever, leukocytosis with neutrophilia, arthralgia, and skin rash. Typical skin rash is an evanescent, salmon-pink erythema predominantly involving extremities, which is included as one of the diagnostic criteria; however, recent findings show that not only typical evanescent rash but also various skin lesions are associated with AOSD. The representative characteristic skin lesion among the non-classical skin rash is called persistent pruritic papules and plaques, which presents erythematous, slightly scaly papules with linear configuration on the trunk. Interestingly, persistent pruritic papules and plaques show unique histological features such as peculiar, distinctive distribution of dyskeratotic keratinocytes in the cornified layers as well as in the epidermis. Other non-classical skin lesions include urticaria. Current insights suggest that several inflammatory cytokines such as interleukin-1 (IL-1), IL-6, IL-18, interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) play a pathogenic role in AOSD. In particular, IL-18 is suggested to play a crucial role in activating macrophages, favoring Th1 type cytokine production. IL-18 induces IFN-γ, IL-17, and TNF-α, which may play an important pathogenic role in AOSD. It is important to recognize the common and/or uncommon skin conditions of AOSD for early correct diagnosis. In this review, various skin lesions are introduced, and the complication with histiocytic necrotizing lymphadenitis (Kikuchi disease) is further discussed.