MOG-IgG–Associated Demyelination Induced by Pembrolizumab Treatment in a Patient With Malignant Melanoma

A 39-year-old man with melanoma who was treated with pembrolizumab for 6 months presented with acute-onset paraparesis. MRI showed multiple contrast-enhancing intraparenchymal lesions in the brain and spinal intramedullary lesions (Figure, A–F). Anti–myelin oligodendrocyte glycoprotein (MOG) antibody immunoglobulin G was positive in serum (1:320) and CSF (1:10). Visual evoked potentials were normal. After methylprednisolone treatment, the limb paraparesis improved, but the tumor lesion enlarged (Figure, H–I). Because of the tumor growth, 1 month later, the patient stopped taking hormones, which led to recurrence of limb paraparesis. Fewer cases of MOG immunoglobulin G–associated neurologic disorders than other CNS demyelination have been described in patients receiving PD-1 inhibitors.1,2