Neuroepidemiology: New Methods, Results, and Challenges in the Definition of the Early Phases of Alzheimer's Disease: Insights From Subjective Memory Complaints and Subjective Cognitive Decline
Neuroepidemiology is the science of neurological research in living human beings. The two main settings of epidemiological studies are the clinical and the population-based, with the last characterized by a more complete and unbiased way to identify all components of the causal chain.
The contemporaneous advancement in knowledge in biology and mechanisms of disease have changed also the parameters to study chronic disease.
In recent years all these changes have produced a new perspective in the epidemiological paradigm and study design, starting with basic definition. The definition of disease is rapidly changing because of the use of new diagnostic techniques with the inclusion of biomarkers (fluid and imaging) in definition criteria of disease entities.
In this complex scenario, in the last few years, new clinical entities have been described for an earlier diagnosis both in population and clinical setting, especially in the Alzheimer disease continuum.
In this chapter, current directions of epidemiological research in neurological diseases will be described providing insights about two clinical entities: subjective memory complaint (SMC) and/or subjective cognitive decline (SCD).
SMC and SCD could be a pre-prodromal stage identifying a phenotype in stage when the neuropsychological testing is still unsensitive or useless for description of individual cases. Help-seeking behavior in subjects with memory decline may occur simultaneously to the later phase of the preclinical stage described by the recent NIA-AA classification system. Therefore, the application of epidemiological methods could help in better identifying firstly cases and build operational boundaries of different categories of several phenotypes in different setting (clinical and community). With this new disease model that starts with assessment of risk factors, the goal of primary prevention is to delay the onset of clinical symptoms.
The ultimate goal of neuro-epidemiological research is to identify causes of disease and implement public health intervention strategies to achieve better brain health during the whole course of life.