A 25-year-old female with papulopustular rash, arthritis, and retinal vasculitis

C A 25-year-old Caucasian female was referred to ophthalmology with a three-week history of decreased vision in her left eye. Review of systems by history and physical exam was positive for dyspnea, a widespread papulopustular rash, heart palpitations, oral and genital ulcers, migratory arthralgia (especially in her knees), and fatigue. Her medical history was significant for past intravenous (IV) drug use. She had initially been seen by a community ophthalmologist and subsequently admitted to the internal medicine service for further investigations due to concerns of significant systemic illness. She was afebrile and her vital signs remained normal. On ophthalmologic exam, her corrected visual acuity (VA) was measured at 6/6 right eye (OD) and 6/60 left eye (OS) and intraocular pressures were 14 mmHg OD and 15 mmHg OS. A subtle relative afferent pupillary defect was noted in the left eye. Slit lamp examination was unremarkable and no vitritis was noted. Extra-ocular movements were full. Fundoscopic examination revealed bilateral intra-retinal hemorrhages and perivascular sheathing (Figure 1). Roth spots (white centered hemorrhages), cotton-wool spots, and optic nerve edema were noted OS. Systemic investigations were initiated and targeted towards a differential diagnosis including inflammatory (e.g., systemic lupus erythematosus, reactive arthritis, vasculitis, sarcoidosis, inflammatory bowel disease), infectious (e.g., human immunodeficiency virus, syphilis, tuberculosis, Lyme disease, infectious endocarditis, disseminated herpetic disease), and other (e.g., disseminated intravascular coagulation, coagulopathy) possible etiologies. A chest x-ray demonstrated no evidence of granulomatous inflammation nor hilar adenopathy and a transthoracic echocardiogram was normal. Initial laboratory investigations showed a mild thrombocytosis (420 x 109/L, normal range 150-350 x 109/L) and elevated C-reactive protein (133 mg/L, normal range 0-8 mg/L). Urinalysis showed 8 RBC/HPF (normal range 0-5) and was positive for leukocyte esterase. Studies for anti-neutrophil cytoplasmic antibodies were negative. A knee joint aspiration was completed and noted inflammatory cells without bacterial growth. Dermatology obtained a skin biopsy of the rash and the resulting pathology showed a mixed perivascular infiltrate with leukocytoclasis (Figure 2). Which of the following is the most likely diagnosis?