As immune checkpoint inhibitors (ICIs) become a mainstay of treatment for several malignancies, neurological complications associated with their use have been increasingly recognized. We present a case of mononeuropathy multiplex (MM) in the setting of durvalumab (PD-L1 inhibitor) use.

A 68-year-old man with stage III non-small cell lung cancer (NSCLC) was seen for the evaluation of asymmetric, painful bilateral upper extremity weakness of 2 months’ duration. He had pre-existing painless glove-and-stocking sensory loss, attributed to cisplatin-induced peripheral neuropathy. Following 4 cycles of cisplatin-based chemotherapy, the patient was started on durvalumab 4 months prior to presentation.

Key exam findings included weakness affecting right digit I flexion, wrist and finger extension as well as left interphalangeal joint flexion affecting digits II-V, glove-and-stocking sensory loss, and diffuse areflexia. Upper extremity EMG findings were notable for active denervation changes restricted to multiple bilateral radial- and median-innervated muscles.

Following initial assessment, the right wrist drop continued to progress, and a decision was taken to discontinue durvalumab given the concern for peripheral neurotoxicity. The left arm weakness resolved over 3-4 weeks, while the right wrist drop had improved only partially at last assessment 5 months later. The patient had declined a trial of steroids or IVIG.

The clinical and EMG findings were consistent with MM and bore a temporal relation to durvalumab use. No alternate etiology was identified. ICI-mediated toxicity can result in sensory, motor and autonomic peripheral nerve involvement with a myriad of clinical presentations. In the existing literature, MM has been described with both ipilimumab and nivolumab, but to our knowledge, this is the first reported case of MM with durvalumab use.

Early identification of often severe neurological adverse events is crucial due to implications for treatment and decisions regarding continued immune checkpoint therapy.