Innovative immunotherapy in the form of Immune Checkpoint Inhibitors (ICIs) has significantly improved outcomes for patients with numerous metastatic cancers. A double-edged sword, we are increasingly learning about the immune-related adverse events (irAEs) associated with use of these novel therapeu- tic agents.

Here we present the case of a 53 years old woman with background of malignant melanoma of the leg and metastatic lesions to the lung and brain. She commenced treatment with dual immunotherapy with Nivolumab/Ipilimumab with subsequent resolution of both metastatic lesions.

Two years following the completion of immunotherapy, she developed left sided arm and leg weakness, hemianopia, left sided Epilepsia Partialis Continua (EPC) and cognitive decline. MRI showed diffusion res- triction along the active cortex during the period of EPC that settled as AEDs suppressed clinical seizure activity. However, while there was no tumour recurrence with interval oncology MRI, there was progressive asymmetrical atrophy of the right cerebral hemisphere with associated white matter signal abnormality in keeping with Rasmussen’s encephalitis scan changes.

We propose that this represents a late delayed reaction to immunotherapy, beyond the recognised encephalitis that was the likely cause of EPC. Increasing use of ICIs will likely reveal more cases.