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Presenilin-1 mutation associated with amnesia, ataxia, and medial temporal lobe T2 signal changes

In the correct clinical context, an important cause of medial temporal MRI signal abnormality is herpes simplex encephalitis. In more subacute presentations, autoimmune or paraneoplastic limbic encephalitis are common etiologies. We present a man with subacute onset of memory impairment and gait ataxia whose MRI was suggestive of limbic encephalitis. After exclusion of infectious causes, immunosuppression was started. He eventually proved to have Alzheimer disease (AD) due to the S170F mutation in the presenilin 1 (PS-1) gene.

### Case report.

A 34-year-old welder presented to our neurology department with memory impairment and unsteadiness. His work colleagues reported a few months' history of frequently loosing his tools and difficulties with his balance.

When examined he was disorientated in time and he had no recall of a name and address after a 5-minute delay. There was head titubation, truncal, mild finger-nose, and gait ataxia. Diadochokinesis was poor bilaterally. Otherwise the examination was normal.

MRI showed generalized cerebral (figure e-1 on the Neurology ® Web site at www.neurology.org) and cerebellar atrophy, increased signal from both hippocampi and amygdalae …