A 59-year-old woman comes to the physician for a 2-month history of pain in her hands and a rash on her legs. She is afebrile. She recalls no recent illnesses or unusual exposures. Physical examination shows palpable purpura on the buttocks, thighs, and lower back. She is currently enrolled in a methadone program. Laboratory studies show decreased serum C4. Which of the following is the most likely diagnosis?
Cold agglutinin disease
Henoch-Schönlein purpura
Leukocytoclastic vasculitis
Serum sickness
Systemic lupus erythematosis
Henoch-Schönlein purpura
Leukocytoclastic vasculitis
Serum sickness
Systemic lupus erythematosis
