Alzheimer’s Disease: Diagnostic Tests

Obligatory medical device diagnostics.

• Magnetic resonance imaging of the skull (cranial MRI, cranial MRI, or cMRI) for basic diagnosis – to exclude space-occupying lesions and to assess signs of atrophyNote: The specificity of structural MRI is too low to base differentiation of AD or frontotemporal dementia from other neurodegenerative dementias on this alone. In addition to imaging (extent and location of vascular lesions), history, clinical findings, and neuropsychological profile should be used to determine vascular dementia. Recommendation grade B
• Computed tomography of the skull (cranial CT, cranial CT, or cCT) for basic diagnosis (if MRI is not available)-to exclude space-occupying lesions and assess signs of atrophy.

Optional medical device diagnostics – depending on the results of the history, physical examination, laboratory diagnostics and obligatory medical device diagnostics – for differential diagnostic clarification or to exclude complications.

• Encephalogram (EEG; recording of the electrical activity of the brain) – for suspected seizure disorders, delirium, Creutfeldt-Jacob disease.
• A PET or SPECT to detect a dopaminergic deficit can be used in clinically unclear cases for the differential diagnosis of Lewy body dementia vs non-Lewy body dementia:
  • Single-photon emission tomography (SPECT) suitable for diagnosis of AD as well as lobar dementias; caveat: availability, lack of studies.
  • Positron emission tomography (PET) measured by fluorodeoxyglucose (FDG)-PET; possibly also PET-MRI – in vivo detection of amyloid beta plaques in patients with AD by amyloid PET possible [hypometabolism in the brain measured by fluorodeoxyglucose, or visualization of β-amyloid plaques by specific radiopharmaceuticals]Cave! A positive amyloid scan does not equate to a diagnosis of AD. A positive amyloid detection by PET must be interpreted in the overall context, especially considering the clinical findings and other biomarker information. Note: A positive amyloid PET finding may indicate underlying Alzheimer’s disease, whereas a negative amyloid PET finding may be against underlying Alzheimer’s disease.
• Doppler sonography (ultrasound examination that can dynamically visualize fluid flow (especially blood flow)) of the carotids (carotid arteries) – indicated in the presence of additional vascular (vessel-related) problems
• Transcranial magnetic stimulation (TMS): procedure with which an electric current is generated painlessly through the intact skull (transcranially) in the brain tissue by means of fluctuating magnetic fields, thereby triggering neuronal action potentials – for differential diagnosis Frontotemporal dementia (FTD)/Morbus Alzheimer’s disease; the procedure can detect Alzheimer’s disease and FTD with a sensitivity (percentage of diseased patients in whom the disease is detected by the application of the procedure, i.e., a positive finding) of 91.8 % and a specificity (probability that actually healthy patients who do not have the disease are also detected as healthy in the test) of 88.8 %. i.e., a positive finding occurs) of 91.8% and specificity (probability that actually healthy people who do not have the disease in question are also detected as healthy in the test) of 88.6

Probable or possible dementia in Alzheimer’s disease with evidence for the pathophysiological process of Alzheimer’s disease: