197 Checkpoint inhibitor associated neuritis a novel pathological entity
Checkpoint inhibitor immunotherapy has revolutionised cancer treatment. However, immunotoxicity due to dysregulated immune control can affect a range of non-cancer tissues causing dermatitis, colitis and endocrinopathies in up to 80% of exposed patients. Peripheral nerve neurotoxicity is rare (<5%) and described as GBS-like or CIDP-like in published case series. Here we present two cases of checkpoint inhibitor associated peripheral neuropathy suggesting this neuritis is a novel pathological entity. Case 1 55-year-old man treated with nivolumab and ipilimumab for renal cell carcinoma developed painful sensory predominant neuropathy after cycle 1. Gait impairment led to discontinuation by cycle 3. NCS revealed axonal loss and conduction slowing but no demyelinating features. He was treated with IVIg without response. Case 2 55-year-old woman with metastatic melanoma was treated with pembrolizumab for 16 months without complication. Within weeks of change to nivolumab she developed painful neuropathic symptoms causing difficulty walking. Neurophysiology was similar to case 1 but she improved to normal with high dose corticosteroids over 4 months. Both sural nerve biopsies showed active large fibre degeneration with diffuse, predominantly T cell inflam- matory infiltrate. No malignant cells. No evidence of a primary demyelinating pathology. This novel inflammatory neuropathy warrants recognition due to alternative treatment response.