Alzheimer's Disease Diagnosis Based on the Amyloid, Tau, and Neurodegeneration Scheme (ATN) in a Real-Life Multicenter Cohort of General Neurological Centers.

BACKGROUND: The ATN scheme was proposed as an unbiased biological characterization of the Alzheimer's disease (AD) spectrum, grouping biomarkers into three categories: brain Amyloidosis-A, Tauopathy-T, Neurodegeneration-N. Although this scheme was mainly recommended for research, it is relevant for diagnosis. OBJECTIVE: To evaluate the ATN scheme performance in real-life cohorts reflecting the inflow of patients with cognitive complaints and different underlying disorders in general neurological centers. METHODS: We included patients (n = 1,128) from six centers with their core cerebrospinal fluid-AD biomarkers analyzed centrally. A was assessed through Aß42/Aß40, T through pTau-181, and N through tTau. Association between demographic features, clinical diagnosis at baseline/follow-up and ATN profiles was assessed. RESULTS: The prevalence of ATN categories was: A-T-N-: 28.3%; AD continuum (A + T-/+N-/+): 47.8%; non-AD (A- plus T or/and N+): 23.9%. ATN profiles prevalence was strongly influenced by age, showing differences according to gender, APOE genotype, and cognitive status. At baseline, 74.6% of patients classified as AD fell in the AD continuum, decreasing to 47.4% in mild cognitive impairment and 42.3% in other neurodegenerative conditions. At follow-up, 41% of patients changed diagnosis, and 92% of patients that changed to AD were classified within the AD continuum. A + was the best individual marker for predicting a final AD diagnosis, and the combinations A + T+ (irrespective of N) and A + T+N+ had the highest overall accuracy (83%). CONCLUSION: The ATN scheme is useful to guide AD diagnosis in real-life neurological centers settings. However, it shows a lack of accuracy for patients with other types of dementia. In such cases, the inclusion of other markers specific for non-AD proteinopathies could be an important aid to the differential diagnosis.

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 ß-amyloid reduction and τ protein increase. Brain imaging showed marked biparietal atrophy and hypoperfusion, and widespread cortical ß-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.