The First Report of Bickerstaff Brainstem Encephalitis Induced by Atezolizumab for Metastatic Breast Cancer.

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment, but they have been known to cause immune-related adverse events (irAEs) by promoting T-cell activation. Neurological irAEs are rare (1%) but have a high fatality rate (11.5%). Here we report the first case of Bickerstaff brainstem encephalitis (BBE) induced by an ICI. A woman in her 60s with metastatic breast cancer was treated with atezolizumab plus nab-paclitaxel once intravenously. Eighteen days later, she lost consciousness with ophthalmoplegia and was diagnosed with a neurological irAE. She recovered consciousness immediately with the administration of intravenous immunoglobulin (IVIG) but suffered severe permanent peripheral neuropathy. Although it is just one case, this experience shows that BBE occurring as a neurological irAE of ICI cancer treatment may be associated with more severe outcomes than conventional BBE in metastatic cancer. Creating a system for multidisciplinary treatment is essential for ICI therapy.