A Case of Multiple System Atrophy with Preexisting Alzheimer's Disease and Predating The Hot Cross Bun Sign

Synucleinopathy, tauopathy and amyloidopathy were classified as distinct clinical and pathological entities in traditional classification systems, and their interactions have been studied on neuropathology and molecular genetics recently.In this report, we present a 69-year-old male patient who had been diagnosed with probable Alzheimer's disease (AD) dementia due to progressive forgetfulness in February 2013. His Mini- Mental State Examination score was 21/30, and his Cognitive Abilities Screening Instrument score was 78/100, resulted from profound deficits in recent memory and abstract thinking domains. Initial brain magnetic resonance imaging (MRI) showed bilateral medial temporal lobe atrophy but was otherwise unremarkable. He presented with new-onset progressive gait disturbance 18 months after the diagnosis of AD, and mild ataxic gait and linear hyperintensity within the midline of the pons on axial T2-weighted MRI were documented. Neither extrapyramidal nor autonomic signs were observed. Ten months later, profound cerebellar signs, urinary incontinence, and mild axial rigidity consistent with the hot cross bun (HCB) sign were noted. Probable multiple system atrophy-cerebellar (MSA-C) type was finally diagnosed by the clinical and neuroimaging features. Of note, his diagnoses of AD and HCB sign predated the diagnosis of MSA-C by 28 and 10 months, respectively.Given that the HCB sign rarely predates overt symptoms or a diagnosis of MSA, we hypothesized that the preexisting amyloidopathy and tauopathy exerted additional neurotoxicity on the synucleinopathy. Key Words: Multiple system atrophy, hot cross bun sign, Alzheimer's disease.