Anti-Sez6L2 antibody-associated autoimmune cerebellar ataxia: a rare case with implications of rituximab therapy.

BACKGROUND: Anti-Sez6L2 (seizure-related 6 homolog-like 2) antibody–associated autoimmune cerebellar ataxia is an exceptionally rare neuroimmunological disorder, with only a limited number of cases reported to date. Its clinical spectrum and optimal therapeutic strategies remain incompletely characterized. CASE PRESENTATION: We report a 77-year-old woman who developed a subacute-to-chronic progressive cerebellar ataxia accompanied by oculomotor abnormalities, a forward-leaning posture, and gait initiation failure.. Neuroimaging studies revealed no structural or neoplastic lesions sufficient to account for the neurological deterioration. Cell-based assays detected anti-Sez6L2 IgG antibodies in both serum and cerebrospinal fluid. The patient exhibited only limited and unsustained improvement following first-line immunotherapies, including corticosteroids and intravenous immunoglobulin. After confirmation of an antibody-mediated mechanism, treatment was escalated to B-cell–depleting therapy with rituximab, resulting in clinical improvement accompanied by a reduction in cerebrospinal fluid antibody titers. CONCLUSION: This case represents a rare presentation of anti-Sez6L2 antibody–associated autoimmune cerebellar ataxia and provides additional clinical and immunological evidence supporting the relevance of this antibody. Furthermore, it suggests that rituximab may represent a potentially valuable therapeutic option in patients with insufficient responses to first-line immunotherapies.