Young-Onset Alzheimer Dementia Due to a Novel Pathogenic Presenilin 1 Variant Initially Misdiagnosed as Autoimmune Encephalitis.

This case demonstrates the importance of considering PSEN1 in young patients with insidious progressive dementia with atypical clinical and neuroimaging features, even in patients without a family history of neurologic disorders. Not adhering to published criteria of possible and probable AE and overinterpretation of subtle inflammatory findings in CSF and MRI contribute to misdiagnosis.