68-year-old white man presents to the emergency room with abdominal pain, nausea and vomiting, and diarrhea. For the past 2 weeks the patient has noted a nodular erythematous rash (shown), arthralgia, and a low-grade fever. Erythrocyte sedimentation rate is 62 mm/hr and C-reactive protein is 20. There is numbness and tingling of the distal right hand and wrist area. Urinalysis is normal but creatinine is 2.2 mg/dL. Antinuclear antibody (ANA), antineutrophil cytoplasmic antibody (ANCA), and rheumatoid factor are negative. diagnosis?