Toxic Encephalopathy After Relapsed Indolent Non-Hodgkin's Lymphoma Following Abrupt Discontinuation of Idelalisib (ZYDELIG®).

Idelalisib is a delta isoform-specific, phosphoinositide 3-kinase (PI3-K) inhibitor. It has been used as a single agent for the treatment of relapsed or refractory small lymphocytic lymphoma (SLL), follicular non-Hodgkin's lymphoma (NHL), and in combination with rituximab for patients with chronic lymphocytic leukemia (CLL). We present a case of a 77-year-old man diagnosed with SLL and was treated with multiple chemotherapeutic regimens in the past. Considering multiple relapses, he was started on idelalisib monotherapy almost 12 months ago. The treatment was stopped due to worsening neutropenia as well as mixed response on the scans. Almost, within one week of stopping the medication, he presented with complaints of altered mental status, hematuria, and worsening of generalized lymphadenopathy. This time, the patient was started on venetoclax (BCL-2 inhibitor) and rituximab which he is tolerating well without any complications.