Multiple system atrophy mimicry in MRI: Watch out for paraneoplastic rhombencephalitis.

The hot cross bun (HCB) sign describes cruciform-shaped T2-weighted hyperintensities of pontocerebellar fibers within the pons and is a typical, but not specific imaging hallmark of the cerebellar variant of multiple system atrophy (MSA-C). We report a case of a 51-year-old woman who was first diagnosed with MSA-C based on progressive cerebellar ataxia, the HCB sign and T2-weighted hyperintensities in middle cerebellar peduncles on MRI. However, further diagnostic work-up revealed positive anti-amphiphysin antibodies in blood and cerebrospinal fluid and subsequently breast cancer. This report of a paraneoplastic rhombencephalitis which initially mimicked MSA-C imaging features stresses the importance of considering immune-mediated rhombencephalitis as differential diagnosis in cases of progressive cerebellar ataxia and the HCB sign on T2-weighted MRI, especially in the absence of pontocerebellar atrophy.