Anti-Rho GTPase-activating protein 26 autoantibody-associated autoimmune cerebellar ataxia with G4 medulloblastoma: A case report and literature review

Abstract Background The Rho GTPase-activating protein 26 (ARHGAP26) antibody, or anti-Ca, was recently identified as a subacute cerebellar ataxia autoantibody. Medulloblastoma is the most malignant brain tumor in children, with G4 medulloblastoma being the most common subgroup. Ten cases involving ARHGAP26 autoantibody-associated autoimmune cerebellar ataxia (ACA) have been reported to date, with an age of onset of 24 to 84 years. Five patients had a history of tumors. However, there is no reported case of ARHGAP26 ACA coexisting with G4 medulloblastoma. Case presentation: Here we report a 28-month-old boy with cerebellar ataxia associated with the presence of anti-ARHGAP26 autoantibody and G4 medulloblastoma. The patient demonstrated gait instability, coughing when drinking, and irritability and was positive for ARHGAP26 antibodies in the serum. Magnetic resonance imaging showed a space-occupying lesion in the fourth ventricle and supratentorial obstructive hydrocephalus. A pathological section of the lesion revealed G4 medulloblastoma originating from the cerebellar vermis. Conclusions This case may further the understanding of anti-ARHGAP26 autoantibody-associated cerebellar ataxia, its age of onset, and associated tumors. This case also suggests a connection between ARHGAP26 antibodies and G4 medulloblastoma. Therefore, we recommend anti-ARHGAP26 antibody testing for patients diagnosed with ACA. Moreover, we propose that simultaneous cerebrospinal fluid (CSF) and serum testing may help elucidate the connection between the presence of a tumor and anti-ARHGAP26 antibodies in the CSF or serum samples. However, in some cases, testing only serum samples may be sufficient for the diagnosis. Although, double sample tests are necessary to explore pathogenic relevance.