Objective: To describe a novel motor phenomenology in an individual diagnosed with anti-DPPX encephalitis at our institution and to compare it with previously known phenotypic presentation of this entity.

Background: Anti-dipeptidyl-peptidase-like protein-6 (DPPX) encephalitis is a rare form of autoimmune encephalitis characterized by the presence of antibodies against DPPX, a subunit of Kv4.2 potassium channels. Characteristic clinical features include rapid onset of cognitive problems, parasomnias, psychosis with hallucinations and seizures. Motor symptoms typically include myoclonus, tremor, and midline ataxia.

Method: Case report with a literature review.

Results: A 35-year-old male presented with three-year history of hallucinations, cognitive decline, gait disturbance, and parasomnias with severe insomnia. His neurologic examination showed midline gait ataxia and bilateral arm tremor. The patient’s level of functionality deteriorated to a level requiring near-total care by his family. At that time, he also developed cervical dystonia with predominant retrocollis and bilateral hand dystonia. Initial autoimmune and reversible encephalopathy workup was negative. MRI was unremarkable and metabolic PET scan showed patchy areas of reduced uptake in both frontal lobes. EEG monitoring did not identify any seizures, but 64-hour EEG recording did not detect any sleep activity during this period.

CSF demonstrated the presence of four oligoclonal bands, and an extended paraneoplastic panel revealed the presence of anti-DPPX antibodies. Treatment with cyclophosphamide and later with rituximab resulted in improvement of his cognitive and psychiatric symptoms, without improvement in his dystonia. Therapy with botulinum A toxin was initiated.

Conclusion: Anti-DPPX encephalitis has distinct clinical features but currently lacks defined diagnostic criteria and treatment guidelines. DPPX encephalitis presenting as new-onset focal dystonia has not been previously described. Our report expands motor phenomenology that may be associated with this autoimmune condition.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dppx-autoimmune-encephalitis-associated-with-severe-multifocal-dystonia/