Mohammed T. Abou-Saleh

222 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYeffects on resulting epidemiological 7 and clinical 8 estimates. This isespecially true with strict exact adherence to each criterion, e.g.when patients whose dementia is too severe to sit for neuropsychologicaltests are said not to have fulfilled the NINCDS–ADRDA criterion that such tests be administered. Now while itmight be argued that there is no point in criteria except in havingstrict adherence to them, we cannot ignore that most such criteriaare revised periodically, and that the operationalization of somecriteria (notably, functional impairment) can vary widely, againwith marked impact on the resulting estimates 9 . A better approachwould be to make clear how the interpretation of specific criteriamay affect a study’s results 7 .Each set of criteria views AD as a diagnosis of exclusion. Giventhat AD is common and that many of the diagnoses to beexcluded are rare, this approach seems perverse, despite theabsence of a biological marker for the most common disorder.Perhaps it is the lack of a detailed consideration of staging,another problem with all the criteria, that has resulted in the‘‘diagnosis of exclusion’’ approach. Without some understandingof systematic variation by stage, the heterogeneity of AD wouldseem chaotic, so that the clinician could only feel confident in thediagnosis when everything else had been rejected. By contrast,recognizing common features in how AD presents and progressesmakes the task of diagnosing it with confidence much easier—indeed, where characteristic milestones are present, such confidencecan extend even to a retrospective diagnosis 10 . This notionof a usual progression is, in fact, implicit in considerations of‘‘atypical presentations’’, which usually are understood as deficits(e.g. aphasia, apraxia) that occur at an uncharacteristically earlystage. Also, in emphasizing insidious onset, the criteria seem toexclude patients whose dementia initially presents with delirium,despite that sequence being a common path to AD 11 .Each set of criteria emphasizes a categorical approach todiagnosis, despite patients who often show more than oneproblem—typically AD and cerebrovascular problems 12 . Whileeach set of criteria allows for ‘‘mixed diagnoses’’, they appear tounderestimate the role of cerebrovascular lesions in both the riskof AD and the degree of its expression 13 .In practice, each set of criteria sees AD chiefly in cognitiveterms. Another way to think of dementia, however, is as a declineof ‘‘effective behaviour’’ 14 —a phenomenon seen often in clinicalpractice, in which cognitive and non-cognitive changes can competefor prominence as the complaints of patients and families. Perhapsit is this experience which underlies the recognition of non-cognitivefeatures in the ICD-10 clinical description, or in the DSM-IVsubtypes. Nevertheless, these non-cognitive aspects have not muchinformed our research understanding of disease presentation, andneither are they likely to. Given the ongoing search for clinicalcorrelates of structural or chemical preclinical features, cognitivedeficits (which are readily quantifiable) are likely to achieve evengreater prominence. Both the near-continuous distribution inneuropsychological test performance scores across an unimpairedto demented range 15,16 and the preference for categories mean thatwe are more likely to see a renewed ‘‘cut points’’ debate than adebate over the meaning of cognitive vs. non-cognitive symptoms asthe basis for future revisions of diagnostic criteria for AD.REFERENCES1. Cohen L. No Aging in India. Berkeley, CA: University of CaliforniaPress, 1998.2. McKhann G, Drachman D, Folstein M et al. Clinical diagnosis ofAlzheimer’s disease: Reports of the NINCDS–ADRDA work groupunder the auspices of the Department of Health and Human ServicesTask Force on Alzheimer’s disease. Neurology 1984; 34: 939–94.3. World Health Organization. The ICD-10 Classification of Mental andBehavioural Disorders. Clinical Descriptions and Diagnostic Guidelines.WHO: Geneva, 1992.4. World Health Organization. The ICD-10 Classification of Mental andBehavioural Disorders. Diagnostic Criteria for Research. WHO:Geneva, 1993.5. American Psychiatric Association. Diagnostic and Statistical Manualof Mental Disorders, 4th edn. Washington, DC: APA, 1994.6. Baldereschi M, Amato MP, Nencini P et al. Cross-national interrateragreement on the clinical diagnostic criteria for dementia. Neurology1994; 44: 239–42.7. Erkinjuntti T, Ostbye T, Steenhuis R, Hachinski V. The effect ofdifferent diagnostic criteria on the prevalence of dementia. N Engl JMed 1997; 337: 1667–74.8. Chui HC, Mack W, Jackson E et al. Clinical criteria for the diagnosisof vascular dementia. A multicenter study of comparability and interraterreliability. Arch Neurol 2000; 57: 191–6.9. Larrea FA, Fisk JD, Graham JE, Stadnyk K. Prevalence of cognitiveimpairment and dementia as defined by neuropsychological testperformance. Neuroepidemiology 2000; 19: 121–9.10. Rockwood K, Howard K, Thomas V et al. Retrospective diagnosis ofdementia using an informant interview based on the brief cognitiverating scale. Int Psychogeriat 1998; 10(1): 53–60.11. Rockwood K, Cosway S, Carver D et al. The risk of dementia anddeath after delirium. Age Aging 1999; 28: 551–6.12. Rockwood K, Wentzel C, Hachinski V et al. Prevalence and outcomesof vascular cognitive impairment. Neurology 2000; 54: 447–51.13. Snowdon DA, Greiner LH, Mortimer JA et al. Brain infarction and theclinical expression of Alzheimer disease. J Am Med Assoc 1997; 277:813–17.14. Torak RM. The Pathologic Physiology of Dementia. New York:Springer-Verlag, 1978.15. Brayne C, Calloway P. Normal aging, impaired cognitive function andsenile dementia of the Alzheimer’s type: a continuum? Lancet 1988; 4:1265–9.16. Ritchie K, Touchon J. Mild cognitive impairment; conceptual basisand current nosological status. Lancet 2000; 355: 225–8.