Isolated fourth cranial nerve palsy in a patient treated with pembrolizumab: a case report.
Matteo Baldi, Sofia Pischedda, Maria Musolino et al.
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Case in brief
A 76-year-old man developed sudden vertical binocular diplopia six weeks after starting adjuvant pembrolizumab following resection of cutaneous melanoma. Examination showed an isolated right superior oblique palsy. Brain and orbital MRI were normal; serum creatine kinase was elevated, but there was no clinical evidence of myocarditis or generalized myopathy. Pembrolizumab was discontinued and low-dose corticosteroids were started. The diplopia progressively resolved, and creatine kinase levels normalized.
What made this case unusual
The presentation was an isolated fourth cranial nerve palsy, an exceptional neuro-ophthalmic presentation temporally associated with pembrolizumab, with normal brain and orbital MRI.
Diagnostic / clinical pearl
In a patient receiving pembrolizumab who develops acute diplopia, consider an isolated ocular motor nerve palsy even when brain and orbital MRI are normal.