Hot cross bun sign in a patient with cerebellar ataxia

A 20-year-old man presented with slowly progressive coordination problems in his trunk and legs for the last 6 years. Examination showed limb, truncal, and gait ataxia. There was impaired deep sensation, proprioceptive deficit, and areflexia of the legs.

T2-weighted Magnetic Resonance Images of the brain showed the “hot cross bun” sign at the level of the pons. A DNA analysis showed increased CAG trinucleotide repeats in the spinocerebellar ataxia (SCA-2) gene on chromosome 12q24.1 [Figure 1].

Figure 1.

Hot cross bun sign seen at the level of the pons on T2-weighted magnetic resonance imaging

Commentary

The hot cross bun sign has mostly been described in patients with multiple system atrophy of the cerebellar type called olivo-ponto-cerebellar atrophy. This finding is related to degeneration of the transverse ponto-cerebellar fibers at the base of the pons, the middle part of the formatio reticularis and the ponto-cerebellar fibers between the lemniscus medialis and the tractus pyramidalis.[1] This case shows that the hot cross bun sign can also be seen in other neurodegenerative cerebellar disorders.[1,2]

SCA is a clinically, pathologically, and genetically heterogeneous group of dominantly inherited neurodegenerative disorders characterized by adult-onset progressive cerebellar ataxia.[3] A recent study suggested an overall prevalence of hot cross bun sign in SCA patients to be 8.7%.[2] The majority of patients with the hot cross bun sign were of the SCA2 subtype. A minority of patients with SCA3 were also positive for the hot cross bun sign.[2] In another study in Western India, a single patient with SCA6 was also positive for the hot cross bun sign.[4] Thus the hot cross bun sign may be present in a spectrum of SCA subtypes.