Insight into global incidence and prevalence of mild cognitive impairment

New research reported today in Paris at the Alzheimer's Association® International Conference 2011 (AAIC 2011) offers insight on the global incidence and prevalence of mild cognitive impairment (MCI) – a condition involving problems with memory or another mental function severe enough to be noticeable to the affected person or to others but not serious enough to interfere with daily life. The research also identifies the conditions that most accurately predict progression from MCI to Alzheimer's disease.

This global perspective on MCI – offered for the first time at AAIC 2011 – includes data from six countries: the USA, Australia, Germany, the UK, Sweden and France.

MCI often - but not inevitably - leads to Alzheimer's disease. As a result of the growing global Alzheimer's epidemic, MCI is receiving increasing attention as the first clinical presentation of Alzheimer's and a potentially pivotal opportunity for intervention. Recently published National Institute on Aging/Alzheimer's Association diagnostic guidelines and criteria – which address pre-clinical Alzheimer's, MCI due to Alzheimer's and Alzheimer's disease dementia – recognize MCI as a critical stage in the Alzheimer's continuum.

"The earlier in the disease process that people at risk for developing Alzheimer's are identified, the sooner we can intervene," said William Thies, Ph.D., Chief Medical and Scientific Officer at the Alzheimer's Association. "Earlier detection will be our best opportunity to prevent continuing damage to the brain, once more effective therapies are developed."

"Understanding MCI is a key to this endeavor. It is has become increasingly important for us to understand how prevalent MCI is throughout the world and how it varies from country to country. These six new studies explore and examine the similarities and differences around the globe," Thies added.

Risk Factors for Progression from MCI to Alzheimer's

While some individuals with MCI do not progress to dementia, identification of factors that enable prediction of progression has emerged as an important Alzheimer's research priority.

"Understanding the multiple causes of MCI, and both the cognitive and biological changes that occur in MCI patients who progress to Alzheimer's, provides a greater opportunity to determine treatment pathways and potentially identify a population for earlier interventions," said Henry Brodaty, M.D., DSc, FRACP, FRANZCP, Professor of Ageing and Mental Health and Director of the Dementia Collaborative Research Centre at the University of New South Wales in Sydney, and Director, Aged Care Psychiatry and Head of the Memory Disorders Clinic at Prince of Wales Hospital.

Data from the six countries suggest that MCI is a surprisingly common condition, especially in industrialized nations, affecting between 15.4 and 42 percent of the studied populations. They also suggest that advanced brain imaging tests and other biomarkers, plus assessment of certain lifestyle-based risk factors, may improve the scientific community's ability to identify who will go on to develop Alzheimer's.

A number of common factors emerge from the studies as indicators of the likely progression from MCI to Alzheimer's, including: depression, apathy, anxiety, age, education, loss of ability in activities of daily living, cardiovascular factors (including stroke and diabetes), and low level of education.  

• In the U.S. study, the risk of progression to dementia was elevated for people with stroke, depression and a high burden of other medical conditions.
• Similarly, in the U.K. and Swedish studies, depression, the presence of other diseases, and MCI affecting several cognitive functions (not just memory) hastened progression to dementia. In particular, in Sweden, diabetes accelerated the progression from MCI to dementia by three years.
• In the study from France, diabetes, stroke and depression were risk factors for progression. In both France and Germany, impairment in activities of daily living was significantly associated with a higher conversion rate and shorter time to onset of dementia.

"There are a variety of types of MCI, and only some forms have a high likelihood of progression to Alzheimer's," said Ronald Petersen, Ph.D., M.D., Professor of Neurology, Cora Kanow Professor of Alzheimer's Disease Research, and Director of the Mayo Alzheimer's Disease Research Center, Mayo Clinic College of Medicine, Rochester, MN.  "The research done to date has shown us that different study populations have different MCI prevalence and incidence rates, so more research needs to be conducted to explore additional similarities and differences between countries and among subpopulations."

"That said, these large data sets are from the major epidemiological studies from around the world. They range from 1,000 to as high as 12,000 subjects who have been followed for long periods of time. The increasing use of imaging techniques along with the new diagnostic guidelines for this group will help further strengthen scientific knowledge about the role of MCI and its impact on Alzheimer's risk," Petersen said.

Subjective Concerns Should Be Taken Seriously

"Another important finding from these multi-country studies is that subjective memory complaints in previously cognitively healthy individuals should be taken seriously as a possible pre-stage of MCI. Individuals who experience memory problems should immediately seek medical evaluation," Brodaty said.

According to experts, early detection allows for prompt evaluation and treatment of reversible or treatable causes of cognitive impairment. For example, if memory or thinking problems are due to depression or insomnia, then there are appropriate treatment interventions that can be applied. If the MCI is due to Alzheimer's, then there are other treatment options that could be explored.

"This is particularly significant as growing evidence suggests that vascular risk factors, such as high blood pressure, diabetes and high cholesterol contribute to cognitive decline. The identification and management of these risk factors at the MCI stage could be an important strategy for preventing and delaying progression to Alzheimer's," Petersen said.