A woman in her 30s presented to the dermatology department (Peking Union Medical College Hospital) with a 5-month history of hemorrhagic blisters and bullae on her lower limbs and buttocks, which was accompanied by intermittent arthralgias. Physical examination revealed tenderness with raised skin temperature and limited mobility of her bilateral knees. Multiple purpuric macules and papules, hemorrhagic bullae, and ulcerations could be seen on her bilateral lower limbs, buttocks, elbows, and dorsal hands. Koebner phenomenon could be seen on her buttocks and thighs (Figure). Results of laboratory tests showed high levels of highly sensitive C-reactive protein (18.33 mg/dL [to convert to mg/L, multiply by 10]) and erythrocyte sedimentation rate (57 mm/h). Serum levels of C3 complement were decreased to 25 mg/dL (to convert to g/L, multiply by 0.01). Autoimmune serology results showed positive antinuclear antibody (1:320) and positive anti–double-stranded DNA antibody (178.42 IU/mL). Antineutrophil cytoplasmic antibody, lupus anticoagulant, anticardiolipin antibody, anti-β2 glycoprotein 1 antibody, rheumatoid factor, and antistreptolysin O results were all negative. Flow cytometer urine sediment analysis showed elevated red blood cell counts (1730.8/μL [to convert to ×106/μL, multiply by 106) with predominant abnormal morphology (60%). Twenty-four–hour urine protein levels were 1.17 g. Histopathological examination of a hemorrhagic blister on her left buttock revealed leukocytoclastic vasculitis. A diagnosis of systemic lupus erythematosus (SLE) was established according to the 2019 European League Against Rheumatism/American College of Rheumatology classification criteria. The patient began a treatment of methylprednisolone, 52 mg per day, and oral cyclophosphamide, 100 mg every other day. She responded well to treatment and continues close follow-up in the dermatology department.