Anti-DPPX encephalitis: Prominent nystagmus reflected by extraocular muscle FDG-PET avidity

Abstract

A 43-year-old Caucasian man developed persistent nystagmus after 10 months of weight loss, diarrhea, insomnia, and 5 months of agitation, memory impairment, and vision changes consisting of nystagmus and double vision. Ocular motor examination demonstrated left-beating nystagmus (LBN), upbeating nystagmus (UBN), and torsional (toward the left ear) nystagmus components (video at [Neurology.org/nn][1]), as well as a left hypertropia from a skew deviation. There was also gaze-evoked nystagmus (GEN) horizontally. General neurologic examination revealed postural tremor in his arms, brisk reflexes, mild dysmetria with finger to nose, and wide-based gait. Detailed neurocognitive testing demonstrated deficits in recall and attention. He had previously been healthy, and his family history was notable only for multiple sclerosis in his brother. Brain MRI showed no abnormalities, and CSF studies showed elevated protein. A broad screen for infections, toxins, and systemic autoimmune disorders was negative. Peripheral blood cell counts were normal. Whole-body 18-fluoro-deoxyglucose PET (18FDG-PET-CT) did not reveal a malignancy, but showed asymmetric avidity of the extraocular muscles (figure). Testing for neuronal autoantibodies revealed a serum dipeptidyl-peptidase-like protein-6 (DPPX) antibody IgG titer of 1:15,360 (Neuroimmunology Laboratory, Mayo Clinic), providing evidence for immune-mediated encephalitis. DPPX antibody from CSF was not tested because of inadequate sample quantity before the initiation of treatment. [1]: /lookup/doi/10.1212/NXI.0000000000000361