Neuronal-specific antibody in patients with multiple system atrophy and progressive supranuclear palsy.

Anti-neuronal antibodies can manifest with diverse movement disorders, including parkinsonism and ataxia, and may mimic neurodegeneration. The prevalence of neuronal-specific antibodies in atypical parkinsonism remains unclear. We examined 166 patients, including 136 patients with clinically diagnosed progressive supranuclear palsy (PSP) and 30 patients with multiple system atrophy (MSA) from the Taiwan PSP/CBS Consortium using an integrated set of tissue-based immunofluorescence assays and a subsequent fixed cell-based assay as well as confirmatory tests to detect neuronal-specific antibodies. We observed one PSP-Richardson syndrome patient (0.74 %) was CASPR2-IgG positive, and one MSA-cerebellar subtype patient (3.33 %) showed GAD65 positivity with a hot-cross bun sign on MRI. The latter showed clinical improvement after immunotherapy. Neither patient had sleep-related symptoms. These findings indicate that neuronal-specific antibodies may mimic MSA or PSP and warrant antibody testing in atypical parkinsonism to identify reversible autoimmune causes.