Clinical manifestations, before the onset of the disease, there may be sore throat, fever, fatigue and muscle and joint pain and other prodromal symptoms. The skin lesions appear suddenly as subcutaneous nodules of bean or larger size, mostly elevated on the skin surface, with obvious pressure pain, variable number, non-fusing nodules, non-breaking, surface skin is bright red at first, gradually turning to dark red, fading in 2-3 weeks, without leaving atrophy marks. However, new rashes can occur, so sometimes new and old lesions coexist. The lesions are usually found on the extensor side of the lower leg, and may occasionally involve the extremities and trunk.