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 0-470-84641-054Differential Diagnosis of DementiaCharlotte Busby and Alistair BurnsWithington Hospital, University of Manchester, UKWhen approaching the differential diagnosis of dementia, twodistinct but related issues are involved. First, the clinician has toconsider whether the patient is suffering from a dementiasyndrome. Differentiation has to be made from a functionalpsychiatric disorder, such as depression, which may be manifestedas a dementing illness (so-called ‘‘pseudodementia’’ or thedementia syndrome of depression); from an acute organicreaction (acute or subacute confusional state); from the effectsof normal ageing 1 , from pre-existing handicaps; and from thedeleterious effects of drugs. Second, the aetiology of thedementia, in terms of either a potentially reversible or irreversibledementia, has to be uncovered. The process is illustrated inFigure 54.1, although in practice a clinician formulates adiagnosis based on the whole presentation (see also ref. 2).This chapter will not deal with Alzheimer’s disease in detail (seeref. 3) but it will be regarded as a prototype against which otherdisorders can be compared.There are clinical situations in which the diagnosis ofdementia is problematic. These have been well summarized 4and include: early cases (where the effects of normal ageingneed to be considered); patients with a low IQ (whereintellectual symptoms may be noticed early); very old patients,especially when residents of nursing homes, without reliableinformants; patients with impaired vision and hearing; patientswho are mentally handicapped; patients with prominentpsychiatric problems, such as paranoia, dysthymia or personalityproblems; and those with severe physical illness or anintercurrent delirium.When evaluating a patient with possible dementia, thefollowing should be performed 5–7 :. Detailed family and personal history and history of the currentillness from a reliable informant.. Mental State Examination of the patient, with particularreference to the cognitive state (amnesia, apraxia, aphasia andagnosia); more detailed neuropsychological assessment shouldbe considered if particular deficits are suspected).. Physical examination, with particular emphasis on the centralnervous system.. Investigations including haematological and biochemicalblood tests, serum B 12 and folate, thyroid function tests,chest X-ray and ECG.Some form of assessment of cerebral function/structure isdesirable, the nature of the investigation being dependent onlocal facilities. An electroencephalogram (EEG) should beperformed and is widely available. Ideally, a computed tomography(CT) scan should also be carried out, but this is not alwayspracticable. If so, it is reasonable to limit this examination to casesin whom there is reason to suspect an intracranial lesion, i.e.clinical suspicion of such a lesion, evidence of cerebral infarction,focal neurological signs, seizure activity, a head injury thought tobe contributory to the clinical picture, or a suspicion of normalpressure hydrocephalus. The main conditions in the differentialdiagnosis of dementia and possible causes of the dementiasyndrome are discussed below.ACUTE CONFUSIONAL STATE (DELIRIUM)This is the most important differential diagnosis to be considered,as there is almost always a physical disorder underlying itspresence. Onset is acute, disturbances often severe and the patientis usually brought to the attention of the services by worriedfriends, relatives or neighbours. There is a global disturbance ofcognition, with marked fluctuation over the course of the day,often worse at night 8 .During affected periods, there is almost always somedisorientation. Among the disturbances are disorders ofperception (characterized by an inability to interpret eventsand to discriminate them from images and dreams), disordersof thinking (disorganized, fragmented and with disjointedthoughts and decreased ability to plan or solve problems) anddisorders of memory (registration, retention and retrieval are allaffected). Clouding of consciousness is the cardinal feature ofdelirium and has been defined in terms of a disorder ofattention (decreased or increased alertness, selectiveness anddirectiveness) and wakefulness (diminished night sleep 9 ). Psychomotorbehaviour is usually disturbed, with overactivity,underactivity or a mixture of the two. The diagnosis of acuteconfusion is made on a characteristic history of a sudden onsetof disturbance and the findings outlined above on examinationof the patient. Often the physical precipitant is not obviousinitially (and in a proportion of cases is never discovered). Anunderlying dementia may be present and is suggested by thehistory.PSEUDODEMENTIAIn this condition, symptoms of disorientation and memory lossoccur in a non-organic psychosis and mimic dementia. Theoriginal description of cases included patients with a number offunctional psychiatric disorders 10 , but in practice depression isby far the commonest cause. In contrast to dementia, theclinical course of the condition is relatively short and has adefined date of onset. There is often a previous history and/or aPrinciples 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