Progressive Chorea Responsive to Immunotherapy: Anti-CASPR2 Antibody Encephalitis Initially Misdiagnosed as Huntington’s Disease
Objective:
We describe a patient with progressive chorea that was initially diagnosed with Huntington’s disease but later found to have anti-CASPR2 antibody positivity and had a robust response to immunotherapy.
Background:
Progressive chorea is commonly associated with either genetic or neurodegenerative disorders like Huntington’s disease. However, treatable causes such as immune mediated conditions are in the differential and should not be missed. CASPR2 is a component of the voltage gates potassium channel complex (VGKC). While antibodies targeting LGI1, another component of VGKC, cause a limbic encephalitis picture, CASPR2 antibodies are known to mediate a wider variety of neurological autoimmunity including central as well as peripheral nervous systems
Design/Methods:
Case Report
Results:
In 2022, a 48-year-old male presented 8-year history of progressive abnormal movements, including chorea, dystonia, and tics, accompanied by irritability, sleep disturbance, and cognitive complaints. He was diagnosed with Huntington’s disease, started on tetrabenazeine and referred for subspecialty evaluation. Genetic testing was negative (16 CAG repeats). He was treated with high dose steroids with minor improvement, leading to further investigations. CSF showed no pleocytosis, mildly elevated protein and normal CSF cytology. A Mayo antibody panel was positive for anti-CASPR2 antibody. He was treated using steroids and PLEX resulting in 80% improvement in chorea. He was able to discontinue tetrabenazine. Maintenance immunotherapy was started with rituximab, and mycophenolate was added as he did not feel rituximab was adequate. On the combination, he has had near-complete resolution of his abnormal movements.
Conclusions:
This case illuminates the value of considering immune-driven pathogenesis in newly diagnosed movement disorders.
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