Fever, rash, and leukopenia in a 32-year-old man · Dx?

A 32-year-old man was admitted to our hospital with fever, chills, malaise, leukopenia, and a rash. About 3 weeks earlier, he'd had oral maxillofacial surgery and started a 10-day course of prophylactic amoxicillin/clavulanic acid. Fifteen days after the surgery, he developed a fever (temperature, 103° F), chills, arthralgia, myalgia, cough, diarrhea, and malaise. He was seen by his physician, who obtained a chest x-ray showing a lingular infiltrate. The physician diagnosed influenza and pneumonia in this patient, and prescribed oseltamivir, azithromycin, and an additional course of amoxicillin/clavulanic acid. Upon admission to the hospital, laboratory tests revealed a white blood cell count (WBC) of 3.1 k/mcL (normal: 3.2-10.8 k/mcL). The patient's physical examination was notable for lip edema, white mucous membrane plaques, submandibular and inguinal lymphadenopathy, and a morbilliform rash across his chest. Broad-spectrum antibiotics were initiated for presumed sepsis. On hospital day (HD) 1, tests revealed a WBC count of 1.8 k/mcL, an erythrocyte sedimentation rate of 53 mm/hr (normal: 20-30 mm/hr for women, 15-20 mm/hr for men), and a C-reactive protein level of 6.7 mg/dL (normal: <0.5 mg/dL). A repeat chest x-ray and orofacial computerized tomography scan were normal. By HD 3, all bacterial cultures were negative, but the patient was positive for human herpesvirus-6 on viral cultures. His leukopenia persisted and he had elevated levels of alanine transaminase ranging from 40 to 73 U/L (normal: 6-43 U/L) and aspartate aminotransferase ranging from 66 to 108 U/L (normal range: 10-40 U/L), both downtrending during his hospitalization. He also had elevated levels of antinuclear antibodies and anti-Smith antibody titers. A posterior-auricular biopsy was consistent with lymphocytic perivasculitis. The rash continued to progress, involving his chest, abdomen, and face. Bacterial and viral cultures remained negative and on HD 4, broad-spectrum antibiotics were discontinued.