A 45-year-old woman presented with impaired cognition. Her medical history included diffuse large B-cell non-Hodgkin lymphoma (Ann Arbor stage IV) involving the thyroid and mesentery, which was diagnosed in spring 2014 and treated with 3 cycles of R-CHOP (rituximab, cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisolone) chemotherapy. Two months later, a positron emission tomography scan revealed a partial response to the chemotherapy.