The 'hot cross bun' sign in the patients with spinocerebellar ataxia

The 'hot cross bun' sign (HCBS), typically seen in the patients with multiple system atrophy, refers to a cruciform hyperintensity in the pons on T2-weighted MRI. Little is known about its pathological basis and prevalence in other degenerative cerebellar diseases and healthy population. We investigate the frequency of HCBS in the patients with spinocerebellar ataxia (SCA) and healthy controls. The presence of HCBS on T2-weighted axial MRIs from 138 SCA patients (three SCA1, 35 SCA2, 76 SCA3, 18 SCA6, one SCA7, three SCA8, and two SCA17) and 102 healthy controls was evaluated retrospectively. The overall prevalence of HCBS in the SCA patients is 8.7%, but the frequency varies in different subtypes: 25.7% in SCA2, 1.3% in SCA3, and none in SCA6 or healthy controls. Notably, one patient with SCA7 and one with SCA8 were also found to have HCBS. The differential list of HCBS should be expanded to include SCA7 and SCA8. The elucidation of frequency of HCBS in various SCA subtypes may help prioritize the genetic testing in late-onset dominant ataxia.