Idiopathic sporadic
ataxia (ISA) is the clinical term for nonfamilial
ataxia with adult-onset and a slowly progressive course. However, immune-mediated
cerebellar ataxia cannot be completely excluded from ISA. The current study investigated the neuropil
antibodies against
cell-surface antigens and clarified the clinical features and neuroimaging findings of patients with these
antibodies. Using tissue-based immunofluorescence assays (TBAs), we examined
antibodies against the cerebellum in serum samples from 67 patients who met the ISA diagnostic criteria, including 30 patients with
multiple system atrophy with predominant cerebellar features (MSA-C) and 20 patients with
hereditary ataxia (HA), and 18 healthy control subjects. According to the TBA results, we divided subjects into three groups: subjects positive for neuropil
antibodies, subjects positive for intracellular
antibodies only, and subjects negative for
antibodies. We compared clinical features and neuroimaging findings in ISA patients among these three groups. The prevalence of neuropil
antibodies in ISA (17.9%) was significantly higher than that in MSA-C (3.3%), HA (0%), or healthy subjects (0%). The neuropil antibody-positive ISA patients showed pure
cerebellar ataxia more frequently than the other ISA patients. Two neuropil antibody-positive patients showed significant improvement of
cerebellar ataxia after
immunotherapy. We detected neuropil
antibodies in 17.9% of ISA patients. Characteristic clinical features of neuropil antibody-positive ISA patients were pure
cerebellar ataxia. Some cases of neuropil antibody-positive ISA responded to
immunotherapy.