Mohammed T. Abou-Saleh

Principles and Practice of Geriatric Psychiatry.Editors: Professor John R. M. Copeland, Dr Mohammed T. Abou-Saleh and Professor Dan G. BlazerCopyright & 2002 John Wiley & Sons LtdPrint ISBN 0-471-98197-4 Online ISBN 0-470-84641-056Minor Cognitive ImpairmentKaren Ritchie and Jacques TouchonINSERM E99-30, Montpellier, FranceNormal cognitive functioning in the elderly has commonly beenconceptualized as the range of performance found in personswithout identified pathology. Comparisons of mean performancebetween age cohorts show decrement with increasing age, whichhas been attributed in the past to normal physiological ageingprocesses. So-called ageing-related cognitive impairment, whilebeing considered ‘‘normal’’, nonetheless has been of interest toclinicians because of the physical dependency it engenders, and assuch it has been given independent nosological status. A numberof concepts have been proposed to describe this tail-end of thenormal cognitive range, beginning with the notion of ‘‘benignsenescent forgetfulness’’, first proposed by Kral 1 . The publicationof formal diagnostic criteria for minor cognitive impairment as‘‘age-associated memory impairment’’ (AAMI) was undertakenby Crook et al. 2 for the National Institute of Mental Health.AAMI refers to subjective complaints of memory loss in elderlypersons verified by a decrement of at least one standard deviationon a formal memory test in comparison with means establishedfor young adults.As memory impairment in the elderly is more commonlyobserved to be accompanied by deficits in other areas of cognitiveperformance, an alternative concept, ageing-associated cognitivedecline (AACD), has been proposed by the InternationalPsychogeriatric Association in collaboration with the WorldHealth Organization 3 . AACD refers to a wider range of cognitivefunctions (attention, memory, learning, thinking, language andvisuospatial function), and is diagnosed by reference to norms forelderly subjects. Application of AACD and AAMI to elderlypersons within the general population suggests that they aredistinct clinical entities, the latter referring to a more severe stateof impairment 4 .More recently, recognition that the wide variability incognitive functioning observed in the normal elderly may bedue at least in part to the inclusion in this group of personswith prodromal dementia or other sub-clinical syndromes hasled to the generation of alternative formulations, which situateminor cognitive impairment as potential pathology, for whichthe clinical response should be therapeutic rather thanpalliative. Within the 10th revision of the InternationalClassification of Diseases (ICD-10) 5 , criteria are given for‘‘mild cognitive disorder’’ (MCD), which refers, like AACD, toa broader range of cognitive disorders than memory, demonstrableby formal neuropsychological testing and hypotheticallyattributable to cerebral disease or damage or to systemicphysical disease known to cause dysfunction. MCD is thusconstrued as being secondary to physical illness or impairment,excluding dementia, amnesic syndrome, concussion or postencephaliticsyndrome. MCD is also applicable to all ages, notjust the elderly. Early attempts to apply MCD criteria topopulation studies of elderly persons has so far met withlimited success, which has cast doubt on the validity of MCDas a separate nosological entity 22 . On the other hand, Gutierrezet al. 6 , arguing for the inclusion of a similar category in DSM(‘‘mild neurocognitive disorder’’) have reviewed numerousstudies implicating diverse forms of underlying pathology, inwhich such a nosological category would have been appropirate.Early evidence that elderly persons with minor cognitivedisorder may be at high risk of developing senile dementia hasled to the development of the concept of ‘‘mild cognitiveimpairment’’ (MCI) 7 . MCI has provoked considerable interestamongst clinicians and the pharmaceutical industry, as it refersto a much larger potential therapeutic target group than seniledementia. As such, it is likely to become a more widely-adoptedconcept than its predecessors. The essential feature of MCI isthat it is a pathological state that is potentially progressive.Beyond this, specific diagnostic criteria found in the currentliterature are inconsistent. Petersen et al. 7 initially refer to‘‘complaints of defective memory’’ and ‘‘demonstration ofabnormal memory functioning for age’’, with normal generalcognitive functioning and conserved ability to perform activitiesof daily living. A later definition refers to ‘‘memory impairmentbeyond that expected for both age and education level’’ 8 .Krasuki et al. 9 refer to cognitive impairment with a score of 20or more on the MMSE, and Zaudig 10 defines MCI as a score ofmore than 22 on MMSE or 34–47 on the SIDAM dementiascale. Others have referred to criteria based on the ClinicalDementia Rating Scale or the Global Deterioration Scalescores 11,12 .A central problem in the definition of MCI has been whether ornot it should be confined exclusively to isolated memoryimpairment. Petersen et al. 8 specify that in MCI generalintellectual functioning should be preserved, and that onlymemory should be affected, as it is the restriction of theimpairment to amnesic abilities which differentiates the syndromefrom AD. Isolated memory impairment was observed by theauthors in a series of 76 MCI subjects; however, this appears tohave been part of the diagnostic criteria for entry into the study,so that the situation is somewhat circular. Apart from the generalproblem of cognitive domain specificity in neuropsychometrictesting (i.e. ascertaining that poor performance on a memory taskis purely related to memory and does not implicate otherfunctions, such as attention and language comprehension), otherresearchers have noted that subjects with MCI, althoughprimarily having memory complaints, also commonly showdeficits in other cognitive domains 11–14 . If the concept of MCI isPrinciples and Practice of Geriatric Psychiatry, 2nd edn. Edited by J. R. M. Copeland, M. T. Abou-Saleh and D. G. Blazer&2002 John Wiley & Sons, Ltd