Neuroimaging features of immune-related adverse events due to immune checkpoint inhibitor therapy.

Immune checkpoint inhibitors, a type of intravenous immunotherapy targeting T cells, are being increasingly used in cancer treatment. They work by increasing the immune system's response to tumour cells, through blockade of inhibitory "checkpoint" receptors. Immune checkpoint inhibitors commonly induce immune-related adverse events (irAEs) affecting multiple organ systems. Hypophysitis is strictly an endocrine irAE, but is the most common irAE identified on neuroimaging. True neurologic irAEs are rare and widely varied. Examples include meningitis, encephalitis, vasculitis, demyelinating syndromes and neuritis. Some neurologic irAEs are not associated with neuroimaging findings (for example, neuromuscular junction disorders), while in others, imaging findings are present in only a proportion of patients (for example, encephalitis). Diagnosing, or at least considering, a neurologic irAE is important for instigating the appropriate management and optimising patient outcomes. This educational review illustrates irAEs that may be identified on neuroimaging and provides practical tips for optimising diagnosis, including relevant clinical considerations. CRITICAL RELEVANCE STATEMENT: Immune checkpoint inhibitors, which are being increasingly used in cancer treatment, commonly induce immune-related adverse events. This educational review illustrates the range of immune-related adverse events for which neuroimaging plays a key role in diagnosis. KEY POINTS: Immune checkpoint inhibitors commonly result in immune-related adverse events (irAEs) affecting multiple organ systems. Hypophysitis, the most common irAE identified on neuroimaging, is characterised by transient pituitary enlargement. True neurologic irAEs are rare and include meningitis, encephalitis, vasculitis, demyelination and neuritis. An understanding of the overall clinical picture is important for supporting the diagnosis.