Bilateral optic neuritis attributed to Pembrolizumab: A case report

Immunotherapy has revolutionised cancer treatment over the past decade and is now well established in the management of a range of cancer primaries, including non-small cell lung cancer. Pembrolizumab acts as a checkpoint inhibitor through programmed death protein 1 (PD-1) inhibition. However, the use of immune checkpoint inhibitors can be complicated by immune-related adverse events (irAE). Neurological complications are rare but are associated with high morbidity compared to other irAE.

Here we report a rare case of bilateral optic neuritis following Pembrolizumab in a patient treated for metastatic lung adenocarcinoma. The patient had also received whole brain radiotherapy during the course of the treatment. Symptom onset occurred during maintenance treatment and at twelve months after first commencing systemic anticancer treatment. Fundoscopy demonstrated optic disc pallor with enhancement of the optic nerves and optic chiasm was seen on Magnetic Resonance Imaging. Symptoms were refractory to steroid treatment and resulted in chronic and profound visual impairment.