A 30-year-old woman with Sjogren syndrome presents with a 24-hour history of a purpuric skin rash. Which of the following is the most likely diagnosis?

Purpura or skin rash in a patient with a known autoimmune disease, such as Sjogren syndrome or systemic lupus erythematosus, is usually attributed to hypersensitivity vasculitis. This vasculitis is caused by the deposition of immune complexes in dermal venules. The other choices are not primarily immune complex diseases.