Pembrolizumab-induced acute right L5 neuritis unresponsive to steroids

We present a case of a patient with metastatic lung adenocarcinoma who developed severe right lower limb radicular pain in a L5-S1 dermatomal distribution 5 months into treatment with carboplatin, pemetrexed and pembrolizumab. MRI of the lumbar spine demonstrated contrast enhancement of the right L5 nerve root consistent with neuritis. The patient was treated with intravenous methylprednisolone 2 mg/kg/day for 3 days, followed by oral prednisolone 1 mg/kg/day with a slow wean over 6 weeks. There was no improvement and their performance status deteriorated to an Eastern Cooperative Oncology Group (ECOG) score of 3, representing capability of only limited self-care. We commenced induction therapy with intravenous immunoglobulin 2 g/kg over 5 days, which resulted in complete resolution of pain sustained for 3 weeks before recurrence of symptoms. We continued maintenance therapy with intravenous immunoglobulin 0.4 g/kg over 2 days at 4-5 weekly intervals, which led to resolution of symptoms and ECOG score to 1.