Anti-Ca/anti-ARHGAP26 antibodies associated with cerebellar atrophy and cognitive decline.

Recently, we identified a novel Purkinje cell-specific autoantibody (termed anti-Ca) targeting rhoGTPase-activating-protein-26 (ARHGAP26) in a patient with cerebellar ataxia. Here we describe a new case of anti-Ca/ARHGAP26 antibody-positive cerebellar ataxia. Cerebellar ataxia was associated with signs of possible limbic encephalitis in this case. The 24-year-old man presented with subacute pancerebellar ataxia, flattened affect, and cognitive decline. Neuropsychological testing revealed working memory deficits, compromised verbal learning and recall, attention deficits, slowed information processing, interference difficulty, and reduced spatial recognition. MRI showed severe pancerebellar atrophy. Serological examinations revealed high-titre anti-Ca/anti-ARHGAP26 antibodies. The antibodies belonged to the IgG1 subclass and were produced intrathecally. This case further corroborates the association of anti-Ca antibodies with cerebellar ataxia, expands the clinical spectrum, and highlights the necessity of antigen-specific diagnostic testing in immune-mediated cerebellar ataxia.