The hot cross bun (
HCB) sign encompasses a cross-shaped hyperintensity area in the pons on axial T2-weighted magnetic resonance imaging (MRI). The
HCB sign is characteristic of
multiple system atrophy (MSA) and has occasionally been observed in other
neurological disorders. Here, we report an autopsied case of
corticobasal degeneration (CBD) that showed the
HCB sign. A female patient presented with progressive gait disturbance and
cognitive impairment at the age of 60 years. A neurological examination revealed
dysarthria,
muscle rigidity of the limbs, akinesia,
truncal ataxia,
urinary incontinence, and
dementia. The
HCB sign was observed on a brain MRI at the age of 65 years, and a clinical diagnosis of possible MSA was made. She died of
pneumonia at the age of 67 years. A postmortem observation, provided neuropathological findings characteristic of CBD, including the presence of astrocytic plaques, pretangles, neuropil threads, and ballooned neurons in association with four-repeat-tau aggregation. Interestingly, the pons displayed severe neuronal loss and
astrogliosis that were prominent in the pontine and raphe nuclei. Myelin sheath depletion was prominent in the transverse fibers of the pontine base and the myelinated fibers of the pontine tegmentum in contrast to relative sparing of the pontine corticospinal tract and medial lemniscus. The cerebellar dentate nucleus exhibited neuronal loss and grumose degeneration. Western blot analysis of
sarkosyl-insoluble fractions from brain tissue lysates using an anti-phosphorylated tau antibody identified immunoreactive signal bands in approximately 37-40, 43, 64, and 68 kDa, consistent with CBD. Genetic analysis did not reveal any known pathogenic mutations in the
microtubule-associated protein tau gene (MAPT). Our case was characterized by the
HCB sign and concordant neuropathological changes in the pons. CBD should be considered an underlying pathology of the
HCB sign, even though the pontocerebellar changes would be unusual in CBD cases.