Prevalence and profiles of clinically diagnosed autoimmune cerebellar ataxia in a Japanese nationwide survey.

BACKGROUND

Autoimmune cerebellar ataxia (ACA) is a potentially treatable cause of cerebellar dysfunction, but remains underrecognized because of diagnostic challenges, including limited access to autoantibody testing and heterogeneous clinical presentations. We aimed to describe the clinical and laboratory characteristics of patients with clinically diagnosed ACA (cdACA) in Japan, based on expert diagnoses, and evaluate associations between clinical factors and response to immunotherapy.

METHODS

This study was a retrospective, multi-center, descriptive study based on a two-step nationwide survey. We inquired at facilities accredited by the Japanese Society of Neurology about the number of patients with cdACA. Furthermore, we asked the facilities with cdACA experience for clinical information.

RESULTS

Of 92 cdACA patients, 96.7% had isolated/predominant cerebellar symptoms. Autoantibodies associated with ACA were detected in 47 (51.1%) patients, with glutamic acid decarboxylase (GAD) antibodies being most frequent. 25 (27.2%) patients had concomitant cancer. Among 80 patients who received immunotherapy, 53 (66.2%) responded positively. Responders were more often female (p = 0.006), and had shorter median time to treatment (71 vs 344 days, p = 0.010) and lower CSF protein (40.65 vs 71.05 mg/dL, p = 0.003). Patients without malignancy responded more frequently (p = 0.006).

CONCLUSION

This nationwide study provides the first real-world insights into the clinical characteristics and management of cdACA in Japan. Although these findings should be interpreted with caution due to diagnostic heterogeneity and the retrospective study design, some patients with concomitant cancer may also show functional improvement following immunotherapy. In the future, there should be further accumulation of ACA cases and the establishment of diagnostic criteria for ACA.