Posterior Cortical Atrophy Due to Alzheimer Disease in a Person With Down Syndrome: A Case Report.

Abstract

Atypical variants are rare in genetically determined Alzheimer disease (AD). This case describes a patient with Down syndrome-associated Alzheimer disease (DSAD) who presented with symptoms of posterior cortical atrophy (PCA). We conducted a clinical and cognitive evaluation, <i>APOE</i> genotyping, determination of AD biomarkers in CSF, structural MRI, [18F]FDG-PET, and tau-PET ([18F]PI2620) scans. A 39-year-old man with DS and mild intellectual disability presented with progressive visuoperceptual disturbances over 18 months. Examination revealed global cognitive impairment, with notable visual agnosia and neglect. The patient also exhibited significant constructive and oculomotor apraxia, optic ataxia, alexia, agraphia, and prosopagnosia. The patient was determined to be <i>APOE</i>3 homozygous, and CSF analysis was consistent with AD pathophysiology. T1-weighted MRI revealed predominant parieto-occipital atrophy. FDG-PET showed significant bilateral hypometabolism in the parietotemporal and occipital cortices, and tau-PET demonstrated pathologic uptake in the parietal, precuneus/posterior cingulate, lateral temporal, and occipital cortices. This well-characterized case of PCA syndrome due to AD in a very young patient with DS demonstrates the occurrence of atypical presentations in DS that might be overshadowed by the baseline intellectual disability associated with DS.