Revised criteria for the diagnosis of mild cognitive impairment (MCI) could compromise the diagnosis of Alzheimer's disease (AD) dementia, according to an analysis published online Feb. 6 in Archives of Neurology.
The National Institute on Aging and the Alzheimer’s Association updated criteria for MCI and AD in 2011. The new criteria differentiate MCI and AD on the basis of preservation of functional activities. “The revised criteria for MCI, however, allow considerable latitude as to what represents functional independence and thus blur the categorical distinction between MCI and dementia,” wrote John C. Morris, MD, from the departments of neurology, pathology and immunology and programs in physical therapy and occupational therapy at Washington University in St. Louis.
The revised MCI criteria allow “mild problems” in daily activities, such as bill paying, as characteristic of MCI.
Morris assessed the functional ratings of 17,535 individuals with normal cognition, MCI or AD who were evaluated at Alzheimer’s disease centers on the basis of functional independence as allowed by the revised criteria. The study population included 6,379 individuals with normal cognition, 4,947 with MCI and 6,209 with probable AD.
The author used the Functional Activities Questionnaire (FAQ) and Clinical Dementia Rating (CDR) to assess functional impairment.
“The differentiation between MCI and AD dementia in its earliest symptomatic stages has been based primarily on whether the cognitive impairment interferes with the conduct of daily living,” wrote Morris.
The distinction seemed to suffice as, under previous criteria, 68 percent of individuals with MCI were performing normally. On the other hand, more than 75 percent of individuals with AD had at least slight impairment in these areas, according to previous criteria.
However, with the revised criteria, many individuals currently diagnosed with milder stages of AD dementia could be reclassified as having MCI.
“The elimination of the functional boundary between MCI and AD dementia means that their distinction will be based solely on the individual judgment of clinicians, resulting in nonstandard and ultimately arbitrary diagnostic approaches to MCI.”
The change could impact clinical trials that use progression to AD dementia as an outcome and also confounds comparisons between legacy and new data.
Morris recommended a different approach. He noted MCI is the earliest clinically detectable stage of symptomatic AD and the distinction between the two is difficult. Although the revised criteria suggest “MCI due to AD” as a diagnosis, Morris suggested that some clinicians are reluctant to use the terminology because of uncertainty about progression to AD and the stigma of an AD diagnosis.
Nevertheless, Morris wrote, “The diagnostic overlap for MCI with milder cases of AD dementia is considerable and suggests that any distinction is artificial and arbitrary,” as clinicians often prescribe medications designated for symptomatic AD to individuals with MCI.
“It is now time to advance AD patient care and research by accepting that ‘MCI due to AD’ is more appropriately recognized as the earliest symptomatic stage of AD.”