Introduction: Mild cognitive impairment: beyond controversies, towards a consensus

The concept of mild cognitive impairment (MCI) has received a considerable amount of interest during the last years, especially as a possible prodromal phase of Alzheimer's disease (AD). AD has a long preclinical period, which presents an opportunity for identifying subjects in a phase when pathology has already begun but AD diagnosis is not achievable. Early diagnosis of AD is important to initiate symptomatic treatment, and will be of even greater significance if medications that might delay or halt the dementia process become available. Furthermore, better identification of elderly persons at high risk of future dementia will provide doctors with opportunities for prognostic counselling, and improve health care planning. Due to the worldwide ageing phenomenon, dementia and MCI have growing public health relevance. There is emerging evidence suggesting a high prevalence of cognitive impairment even in younger ages. For all these reasons, the concept of MCI is useful both clinically and as a research entity. However, as the literature of MCI has expanded there has been confusion concerning the specific boundaries of the condition, and controversies regarding its definition, assessment, management and intervention strategies. A greater consensus and standardization of definitions and research methodology for MCI in needed to make further studies more comparable and useful for designing intervention strategies. Persons with MCI are known to have an increased risk of progressing to dementia compared to elderly persons with normal levels of cognitive functioning. However, the evolution is heterogeneous, as some persons have been seen to improve over time, whereas others have an increased risk of mortality. To date, much of the research on MCI has derived from clinical sources, with the focus on symptomatic patients within specialized medical settings, although there are increasing results emerging from population-based sources. The aim of the first Key Symposium was to combine the clinical perspectives with epidemiological evidence to reach a consensus concerning a broader concept of MCI and to identify future research questions. This symposium brought together both a multidisciplinary and a worldwide group of experts to focus solely on this subject. A group of 100 international physicians and researchers from Asia, Australia, Europe and the US met in Stockholm. Five aspects of MCI were covered and presented as articles in this issue, reflecting the authors’ perspectives of the current state of the art: clinical presentation 1, cognitive assessment and markers 2, neuroimaging 3, biomarkers 4 and genetics 5. The meeting concluded with a general discussion followed by a day of deliberations involving the speakers, discussants, chairpersons and the symposium's Scientific Committee. This resulted in a report from this international working group, describing the state of the art of MCI, recommendations for management and treatment, and future research questions 6. The main questions addressed by the working group included whether MCI represents a useful clinical and research entity, as well as the challenge of further refining the criteria so that treatments can be targeted towards a specific MCI population. No conflict of interest was declared.