Hypouricemia in a patient with hereditary xanthinuria type I
A 78-year-old man with primary central nervous system lymphoma was started on rituximab, methotrexate, and corticosteroids. Baseline hepatitis B virus (HBV) serologic tests, 2 months before chemotherapy, showed nonreactive hepatitis B surface antigen (HBsAg) and hepatitis B core total antibody (HBcAb total) results. Chemotherapy was discontinued after 5 months due to worsening cognitive function and chemotherapy-related leukoencephalopathy. 1 month after discontinuation of systemic therapy, the patient