Electrophysiological findings in immune checkpoint inhibitor-related neuromuscular events.

Introduction: Immune checkpoint inhibitors (ICIs) have become key therapies for various malignancies by restoring antitumor immunity. However, they may trigger immune-related adverse events (irAEs), including neurological irAEs (n-irAEs), which, though rare, can be severe. Among these, neuromuscular disorders affecting peripheral nerves, the neuromuscular junction (NMJ), and muscle are the most frequent and carry the highest mortality risk, warranting prompt recognition.

Objective: To describe the clinical and electrodiagnostic features of ICI-related neuromuscular disorders in 38 patients.

Methods: We retrospectively analyzed patients treated with ICIs referred for electrodiagnostic evaluation due to suspected n-irAEs. Patients were categorized into two phenotypes: (1) ir-Neuropathies (cranial/peripheral neuropathies, radiculopathies) and (2) ir-MG/myositis (myasthenia gravis and/or myositis). Studies included motor/sensory conduction, F-waves, needle EMG, and, when indicated, single-fiber EMG, repetitive stimulation, and evoked potentials.

Results: Of 38 patients, 27 (71%) had ir-MG/myositis and 11 (29%) ir-Neuropathies. Myositis with spontaneous activity was the most frequent ir-MG/myositis pattern. In ir-Neuropathies, acute sensory-motor demyelinating polyradiculoneuropathy predominated.

Conclusions: Myositis is the most common ir-MG/myositis pattern, while demyelinating polyradiculoneuropathy is typical of ir-Neuropathies. NMJ dysfunction often coexists with myositis and may be missed electrophysiologically.

Significance: Electrodiagnosis is essential for early detection and management of ICI-related neuromuscular complications.