Characteristics and prognosis of PCA-1 (anti-Yo) autoimmunity and the utility of the Brief Ataxia Rating Scale in a seropositive cerebellar ataxia cohort.

BACKGROUND

Autoimmune cerebellar ataxia (ACA), whether paraneoplastic, classically associated with PCA-1 autoimmunity, or non-paraneoplastic, causes substantial morbidity. Antibodies inform clinical decisions given prognostic differences. The modified Rankin Scale (mRS) and Clinical Assessment Scale in Autoimmune Encephalitis (CASE) underrepresent cerebellar change. We aimed to characterize seropositive ACA, compare PCA-1 with other seropositive cases, identify predictors of poor function, and compare outcome measures.

METHODS

We performed a retrospective cohort study of adults with seropositive ACA at Massachusetts General Brigham (2004-2025). We compared anti-PCA-1 positive with other seropositive cohorts. Time to wheelchair dependence was estimated by Kaplan-Meier and compared by log-rank. Univariable Cox models identified predictors. Outcomes were assessed with mRS, CASE, and Brief Ataxia Rating Scale (BARS).

RESULTS

Nineteen patients (median age 66.3 years; 68.4 % female) were included. Eleven (57.9 %) were anti-PCA-1 positive and all of them were paraneoplastic. Tubo-ovarian serous carcinoma was most common (63.6 %). The anti-PCA-1 positive group was more often female (90.9 % vs. 37.5 % p = 0.04), had worse BARS at last follow up (20 vs. 9.5 p < 0.01), and had higher wheelchair dependence (100 % vs. 37.5 % p < 0.01). Acute onset (< 2 weeks) and PCA-1 positivity were associated with wheelchair dependence. BARS monitored symptoms more precisely than mRS or CASE.

CONCLUSION

In this seropositive ACA cohort, PCA-1 autoimmunity was associated with wheelchair dependence despite immunotherapy and cancer treatment. Acute onset may predict severe decline. A cerebellar symptom specific measure such as BARS may assess clinical change better than mRS or CASE for monitoring ACA.