Neuronal intermediate filament neurologic autoimmunity in a patient with Merkel cell carcinoma receiving pembrolizumab.
Ali Hijazi, Saffet Guleryuz, Mark A Walshauser et al.
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Case in brief
A 55-year-old woman with recurrent stage IIIA Merkel cell carcinoma developed vertigo, gait instability, dysarthria, and persistent right hemifacial and cervical spasms after her second pembrolizumab dose. Brain MRI was unremarkable; continuous EEG showed encephalopathy without a definitive electrocerebral correlate, suggesting subcortical myoclonus. CSF showed lymphocytic pleocytosis and elevated protein, and NIF antibodies were detected in CSF by cell-based assay. Pembrolizumab was stopped, and high-dose corticosteroids followed by monthly intravenous immunoglobulin were given. Her neurologic symptoms nearly completely resolved after 6 months.
What made this case unusual
Persistent hemifacial and cervical spasms were an unusual manifestation of NIF paraneoplastic neurologic autoimmunity in the setting of pembrolizumab-treated Merkel cell carcinoma.
Diagnostic / clinical pearl
With new neurologic symptoms during immune checkpoint inhibitor therapy, consider paraneoplastic NIF autoimmunity; an unremarkable brain MRI does not exclude it, and CSF antibody testing may support the diagnosis.