Biparietal variant of Alzheimer's disease: a rare presentation of a common disease

Alzheimer's disease (AD) is a clinically heterogeneous disease that may have atypical presentations with focal cortical syndromes and relatively preserved episodic memory. The posterior variant of AD has two subtypes: occipitotemporal, presenting with visuoperceptive impairment, and biparietal, presenting with visuospatial dysfunction and apraxia. We report a case of a 51-year-old woman with progressive limb apraxia and choreiform movements. Her neuropsychological evaluation was compatible with dementia, and revealed ideomotor and ideational limb apraxia, severe visuoconstructive ability impairment, dyscalculia and posterior aphasia. Workup excluded metabolic, infectious, inflammatory or neoplastic causes, and hereditary conditions as Huntington's disease and familial AD. Cerebrospinal fluid biomarkers revealed β-amyloid reduction and τ protein increase. Brain imaging showed marked biparietal atrophy and hypoperfusion, and widespread cortical β-amyloid deposition. Biparietal variant of AD was diagnosed and acetylcholinesterase inhibitor treatment induced clinical stabilisation. AD may present with atypical features and a high clinical suspicion is necessary for an early diagnosis.