A. Check antineutrophil cytoplasmic antibody (ANCA) titers
The key to the correct diagnosis is the history of arthralgias, paresthesias, ocular inflammation, palpable purpura, and skin biopsy findings of leukocytoclasia, which is characteristic of small vessel vasculitis. ANCA-associated vasculitis due to granulomatosis with polyangiitis was confirmed with serum indirect immunofluorescence, diffuse cytoplasmic staining ANCA (c-ANCA) (+1:20), and a positive proteinase 3 (PR3) antibody (+51.8).
Chikungunya (choice B) is a mosquito-borne viral illness that may cause arthralgias and conjunctivitis; however, its rash is morbilliform rather than purpuric. Obtaining a transthoracic echocardiogram (choice C) is incorrect because without fevers or history of intravenous drug use, endocarditis is unlikely. While Chlamydia trachomatis (choice D) may cause a reactive arthritis with arthralgias and conjunctivitis, it does not cause cutaneous small vessel vasculitis.