What are the diagnostic criteria for flat warts?

The diagnostic criteria for flat warts mainly include the following: 1. **Lesion characteristics**: The skin lesions are flat, smooth papules the size of a pinhead to a green pea or slightly larger. They are round, oval, or polygonal in shape, firm in texture, and usually the same color as normal skin or light brown. The papule surfaces are smooth and sometimes exhibit mild desquamation of the stratum corneum. 2. **Common locations**: Flat warts commonly occur on the face, dorsum of the hands, and forearms, but may also develop on the soles of the feet, fingers, around the nails, and oral mucosa. The lesions are usually scattered or clustered; in some cases, autoinoculation due to scratching may cause them to arrange in a linear, bead-like pattern along scratch marks. 3. **Subjective symptoms**: Generally, there are no spontaneous symptoms, although occasional mild itching may occur. Prior to regression, the lesions may become itchy and darken in color. 4. **Disease course**: The course of flat warts is chronic and may last for several years, but they may also resolve spontaneously without leaving scars. In some patients, the warts may gradually disappear as immune function improves or following treatment.