Long-standing prion dementia manifesting as posterior cortical atrophy.

Prion diseases commonly manifest with the phenotype of subacute myoclonic encephalopathy. However, genetic forms of prion disease may have prolonged evolution mimicking neurodegenerative disease. We present the clinical and neuropathological features of a family with an early and long-standing dementia manifesting with posterior cortical atrophy and related to a 120 bp insertional mutation of the prion protein gene. Two cases exhibited mixed prion and Aβ pathology. The differential diagnosis with Alzheimer disease is discussed.