General reviewMolecular imaging in the diagnosis of Alzheimer's disease and related disorders

IntroductionThe diagnosis of Alzheimer's disease (AD) and its related disorders rely on clinical criteria. There is, however, a large clinical overlap between the different neurodegenerative diseases affecting cognition and, frequently, there are diagnostic uncertainties with atypical clinical presentations. Current clinical practices can now regularly use positron emission tomography (PET) and single-photon emission computed tomography (SPECT) molecular imaging to help resolve such uncertainties. The Neurology Group of the French Society of Nuclear Medicine and Federations of Memory, Resources and Research Centers have collaborated to establish clinical guidelines to determine which molecular imaging techniques to use when seeking a differential diagnosis between AD and other neurodegenerative disorders affecting cognition.State of knowledgeAccording to the current medical literature, the potential usefulness of molecular imaging to address the typical clinical criteria in common forms of AD remains modest, as typical AD presentations rarely raise questions of differential diagnoses with other neurodegenerative disorders. However, molecular imaging could be of significant value in the diagnosis of atypical neurodegenerative disorders, including early onset, rapid cognitive decline, prominent non-amnestic presentations involving language, visuospatial, behavioral/executive and/or non-cognitive symptoms in AD, or prominent amnestic presentations in other non-AD dementias.Conclusion and perspectiveThe clinical use of molecular imaging should be recommended for assessing cognitive disturbances particularly in patients with early clinical onset (before age 65) and atypical presentations. However, diagnostic tools should always be part of the global clinical approach, as an isolated positive result cannot adequately establish a diagnosis of any neurodegenerative disorder.