A 65-year-old man with a 14-year history of well-controlled HIV infection presented to the emergency department with three weeks of nausea, abdominal pain and confusion. His medical history included chronic obstructive pulmonary disease with features of asthma and infrequent exacerbations, allergic rhinitis, hypertension, dyslipidemia, chronic kidney disease (estimated glomerular filtration rate [eGFR] 30 mL/min/m 2 ), osteopenia, gastresophageal reflux disease, and a remote history of depression. His viral load had been undetectable, with a CD4 count above 400 (normal range 356-1573) cells/µL for many years on a ritonavir-containing antiretroviral regimen. He was also taking intranasal budesonide (total daily dose 128 µg), as well as inhaled budesonide (total daily dose 800 µg) in combination with formoterol. In response to a decline in his bone mineral density, recent progressive renal dysfunction (eGFR had decreased from 60 to 30 mL/min/m 2 over the course of the year) and worsening dyslipidemia, his antiretroviral therapy was changed to abacavir, lamivudine and dolutegravir eight weeks before he presented to the emergency department.Following this change in treatment, the patient was seen in the chronic viral illness clinic, and he reported asthenia, anorexia, nausea and intermittent episodes of crampy epigastric abdominal pain. He was afebrile, his seated blood pressure was 110/70 mm Hg, with a pulse rate at 100 beats/min. The remainder of the physical exam was unremarkable. A contrast-enhanced computed tomography (CT) scan of the abdomen did not show a cause for his abdominal pain.The patient's new antiretroviral regimen was put on hold, and genetic testing for a predisposition to abacavir hypersensitivity was conducted as a possible explanation for his symptoms. Because the patient was volume depleted, treatment with intravenous saline was started. After receiving 3 L of crystalloid, he felt better and was discharged home, with all antiretroviral treatments suspended and follow-up scheduled in clinic.Two weeks after discharge, the patient presented to the emergency department. In addition to intermittent epigastric pain, he now reported five days of headache, worsening fatigue, diffuse arthralgias, myalgias and fever. His wife also reported that he had been having difficulty with difficulty with planning and organizing his daily tasks, short-term memory and finding words. Upon physical examination, his body temperature was 38.9°C, and he had sinus tachycardia of 110 beats/min and a blood pressure of 100/60 mm Hg, which fell to 90/50 mm Hg after one minute of standing. Jugular venous pressure was 0 cm above the sternal angle. The remainder of the physical examination was normal. His Montreal Cognitive Assessment was 14/30, indicating substantially impaired cognitive function.The patient had a CD4 count of 350 cells/µL, and his plasma HIV RNA level had risen from previously undetectable to 1.5 million copies /mL. A plain CT scan of his head was unremarkable. A lumbar puncture was performed and showed an iso...