[Rare forms of dementia-Atypical variants of Alzheimer's dementia].

In Germany, around 1.8 million people currently suffer from dementia and the numbers are increasing. The main cause of dementia is Alzheimer's disease. This is classically manifested in the form of an amnestic syndrome but also encompasses various atypical variants, especially in younger patients and in the clinical routine are not always easy to recognize. These are described in this narrative review with case studies. Posterior cortical atrophy (PCA) presents with visual disorders, in the logopenic variants of primary progressive aphasia (lvPPA) impaired word retrieval is the main symptom, in the frontal variant of Alzheimer's disease behavioral disorders are prominent and in corticobasal syndrome (CBS) an akinetic rigid Parkinson's syndrome with alien limb phenomenon. As the clinical presentation of these atypical variants shows an overlap with other dementia disorders, the differential diagnosis is often challenging. In this context amyloid biomarkers can provide valuable services.