Clinical summary: Itchy pigmented rash is of unknown etiology and is more common in young females, preferably on the neck, back, scapula, chest, followed by the upper arms and trunk. The main clinical manifestations are pale red papules, which may be fused or may appear as a cluster or eczema-like changes, with severe itching. The disease is prone to recurrence in spring and summer, and the recurrence is mainly limited to the original hyperpigmented area, with a disease duration of 0.5-8 years. Histopathology: The histopathological changes are not characteristic, but in the early stage, superficial perivascular neutrophil infiltration can be seen; in the middle and late stage, there are varying degrees of lymphocyte and eosinophil-based infiltration in the superficial dermis. Epidermal changes include hyperkeratosis, lymphocyte emigration, spiny layer edema and basal cell liquefaction degeneration. Treatment: Glucocorticoids and antihistamines are usually ineffective in treating the disease, while ampicillin and memantine treatment can make the rash subside.