Mohammed T. Abou-Saleh

346 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYchanges, which usually begin somewhere around 50 years of age,are age-related and generally more pronounced in men 5 . Ashortened rapid eye movement (REM) latency may be helpful inseparating early dementia (normal REM latency) from depression(shortened REM latency). The former show decreased amounts ofsleep spindles and K-complexes with reduced REM sleeppercentage and a normal REM temporal distribution.EEG IN DEMENTIAWith important exceptions, the changes in dementia are qualitativelysimilar to those of healthy ageing, although the degree ofchange is much more marked. Since the days of Berger, there havebeen many studies of the routine clinical EEG in dementia(reviewed by Busse 6 , Pedley and Miller 7 , Fenton 4 ).times more alpha rhythm and five times more local slow wave fociin MID. Often, the laterality of the EEG focus in MID correlateswith past or present clinical evidence of an ischaemic lesionlateralized to the same side. In contrast, AD patients have asignificantly higher incidence of diffuse delta activity.Huntington’s DiseaseThe EEG in Huntington’s disease differs from the dementiasalready discussed. In a variable number (30–80%) depending onthe series reported, a low voltage tracing with an averageamplitude of 10 mV or less is a characteristic feature. Thisamplitude reduction correlates with caudate nucleus involvementbut only becomes apparent by the time the disease is clinicallywell-established 16,17 .Changes Common to Most Dementing DisordersSlowing of the dominant, parieto-occipital (alpha 8–13 Hz)rhythm over both hemispheres, a moderate to marked increasein generalized theta (4–7 Hz) and delta (1–3 Hz) activity (diffuseslowing) and a bilaterally symmetrical decline in low voltage beta(fast) activity are common background activity changes. Oneautopsy study reports a significant correlation between alphafrequency slowing and the number of senile plaques counted inAlzheimer’s disease (AD) patients’ brains 8 . Paroxysmal runs ofbifrontal delta activity are not uncommon in dementia patients. Inone investigation these have been related to degenerative brainstem changes at autopsy 9 . The occipital responses to photicstimulation at fast flicker rates (equal to or greater than 18 flashes/s) tend to disappear in a significant minority of dementia patients(1 in 5).Differences Between the Various DementiasAD vs. Pick’s DiseaseStudies that have compared the various types of dementingillnesses indicate that less than 5% of patients with histologicallyconfirmed AD have a normal EEG even when first referred to thepsychiatric services 4,10–12 . In contrast, Pick’s disease and multiinfarctdementia (MID) are not infrequently associated withnormal EEGs. The number of Pick’s disease patients in any studyis small, but a consistent finding is that around 50% have normalrecords. Even when diffuse slowing is present in Pick’s diseasepatients, the alpha rhythm is better preserved 9,12,13 . The alpharhythm is generated by the parieto-occipital areas of the cerebralcortex modulated by thalamocortical influences. The histologicalchanges in Pick’s disease are largely confined to the frontotemporalregions, which are relatively ‘‘silent’’ electrically, comparedto the parieto-occipital areas, where the predominant AD changesoccur. Indeed, it has been recently suggested that a normal EEG isone of the characteristic features of dementia of frontal lobe type:a dementing syndrome with onset in the presenium and selectivefrontal lobe dysfunction. It is not clear whether it represents aform of Pick’s disease 14 .Multi-infarct Dementia (MID)The EEG in MID differs from AD in displaying significantly moreasymmetry between the hemispheres, localized slow wave disturbancesbeing particularly common, while the alpha tends to bebetter preserved. For example, Constantinidis et al. 15 report threeThe Significance of Paroxysmal Abnormalities withPeriodocityParoxysmal bifrontal runs of delta waves are common in dementiapatients, especially those with AD. In one histological investigation,this bifrontal delta activity has been related to degenerativebrain stem changes 9 . Regularly recurring (periodic) generalizedbiphasic or triphasic sharp wave or slow wave complexes ofgeneralized origin with a characteristic recurrence rate of 0.5–1.0 s(intervals between successive bursts of complexes) are a characteristicfeature of Creutzfeldt–Jakob disease (CJD). Early in theillness, diffuse background slowing occurs and in most cases thecharacteristic periodic complexes emerge. In a minority of patients(up to one-third in some series), especially the amyotrophic cases,this pattern may not be seen or may appear late. If practical, serialrecordings are recommended 18 . On rare occasions, the periodicdischarges may be temporarily focal, later generalizing andbecoming bilaterally synchronous as the disease progresses.Their presence in a middle-aged or elderly patient with dementiais highly suggestive of CJD. Periodic triphasic waves of generalizeddistribution can be seen in other conditions, notably hepaticand other metabolic encephalopathies, subacute sclerosingleucoencephalitis and Unverricht’s myoclonus epilepsy. Rarelythey may appear in advanced AD patients and in Binswangersubcortical encephalopathy but do not show the characteristicperiodicity or evolution of CJD.EEG, COGNITIVE AND CT SCAN CHANGESMcAdam and Robinson 19 reported a correlation of +0.79between ratings of EEG change and clinical severity in dementiapatients of mixed aetiology. The association between EEGslowing and severity of dementia has been replicated by manysubsequent studies 4,6,20 . However, Johannesson et al. 12 report thatthis electroclinical relationship held for 100% of their AD casesbut almost half of their Pick’s and MID patients had normalEEGs in the presence of significant cognitive decline. Thecorrelation between the EEG slowing and extent of corticalatrophy as measured by computed tomography (CT) is weak, thelink being obvious only in advanced cases. The EEG correlatesbetter with clinical scales sensitive to early dementia, while theconverse is true for the CT scan 20 . Combining the two measuresimproves their diagnostic power. A discriminant function analysisstudy of 56 AD patients and 84 normal controls correctlyclassified 86% using the EEG data and 84% using the CT scaninformation. Combining the EEG and CT scan variablesimproved the correct classification rate to 90% 2 . Interestinglyenough, the degree of functional brain impairment as measured by