Mohammed T. Abou-Saleh

NOSOLOGY OF DEMENTIA 187by embolic phenomena, so that the onset of the clinical conditionwould be sudden and acute. Subsequent further emboli wouldproduce other sudden deteriorations, perhaps followed by someimprovement as areas of brain oedema resolved and somefunction was restored.WMLs refer to the histopathological picture of diffusedemyelination with incomplete infarction in subcortical structuresof both hemispheres, and arteriosclerotic changes with hyalinizationor fibrosis of the small penetrating arteries and arterioles inthe white matter 9 . These lesions may appear as low-density areason computed tomography (CT) scans and as hyperdense areas onmagnetic resonance imaging (MRI). The cognitive decline insubjects with WMLs has been suggested to be caused by adisconnection of subcortical–cortical pathways, producing a declinein abilities related to subcortical or frontal lobe structures.Memory impairment is mandatory for the diagnosis of vasculardementia in ICD-10, DSM-III-R and DSM-IV. This is not idealto describe the cognitive dysfunction in vascular dementia, whereintellectual impairment may be substantial while memorydysfunction is mild 12 . The ICD-10 requires that ‘‘deficits in highercognitive functions are unevenly distributed’’ and DSM-III-R thatthere is ‘‘a patchy distribution of deficits (i.e. affecting somefunctions, but not others) early in the course’’. The latter was,however, no longer included in the DSM-IV.Although stroke increases the risk of developing dementiaseveral-fold 13,14 the contributions of a stroke or an infarct to theclinical symptoms of dementia are not always easy to elucidate.Stroke may be the main cause of dementia in an individual, it maybe the event that finally overcomes the brain’s compensatorycapacity in a subject whose brain is already compromised byAlzheimer pathology, albeit not yet clinically manifest, and inmany instances minor manifestations of both disorders whichindividually would not be enough to produce dementia mayproduce it together 15 . Sometimes the presence of stroke in apatient with AD may be coincidental. Most criteria leave it to theclinician to make the decision whether the cerebrovascular disease‘‘may be judged to be aetiologically related to the dementia’’(ICD-10, DSM-III-R, DSM IV).In most criteria the definition of CVD is based on history orfindings of focal neurological upper motor neuron symptoms/signs, or brain imaging findings of CVD. DSM-IV (Table 36.5)gives examples of signs, while the ICD-10 (Table 36.6) specificallyrequires that at least one should be: (1) unilateral spastic weaknessof the limbs; (2) unilateral increased tendon reflexes; (3) extensorplantar response; or (4) pseudobulbar palsy.The DSM-IV specifies that there should be signs and symptomsor laboratory evidence indicative of CVD (e.g. multiple infarctionsinvolving the cortex and underlying white matter) thatare judged to be aetiologically related to the disturbance, whileICD-10 requires that there should be evidence from history,Table 36.5DSM-IV Vascular dementiaA/B General criteria for dementiaC Focal neurological signs and symptoms, e.g:Exaggeration of deep tendon reflexesExtensor plantar responsePseudobulbar palsyGait abnormalitiesWeakness of an extremityorLaboratory evidence of cerebrovascular disease, e.g.Multiple infarctions involving cortex and underlying white matterthat are judged to be etiologically related to the disturbanceD Do not occur exclusively during deliriumAmerican Psychiatric Association 2 .Table 36.6ICD-10 Criteria for vascular dementia (adapted)G1 The general criteria for dementia (G1–G4) must be metG2 Deficits in higher cognitive function are unevenly distributed, withsome findings affected and others relatively sparedG3 There is clinical evidence of focal brain damage, manifest as at leastone of the following:(1) Unilateral spastic weakness of the limbs(2) Unilaterally increased tendon reflexes(3) An extensor plantar response(4) Pseudobulbar palsyG4 There is evidence from the history, examination, or tests of asignificant cerebrovascular disease, which may reasonably bejudged to be etiologically related to the dementiaWorld Health Organization 3 .examination or tests of a significant CVD, which may bereasonably judged to be aetiologically related to the dementia(e.g. history of stroke or evidence of cerebral infarction). In theNational Institute of Neurological Disorders and Stroke and theAssociation Internationale pour la Recherche et l’Enseignementen Neurosciences (NINDS–AIREN) criteria 10 (Table 36.7), adiagnosis of probably vascular dementia requires that focal signsconsistent with stroke and relevant CVD by brain imaging shouldbe present. Tatemichi, one of the authors of the NINDS–AIRENcriteria, and his colleagues published a modified version 16 , inwhich this criterion was changed to focal signs consistent withstroke or relevant CVD by brain imaging. The first criterion isprobably too strict and underestimates the occurrence of VaD; thelatter criterion may be too broad. The NINDS–AIREN criteriarecommend that a diagnosis of ‘‘possible’’ vascular dementia maybe made in the presence of dementia with focal neurological signsin patients in whom brain imaging studies are missing; or in theabsence of a clear temporal relationship between dementia andstroke; or in patients with subtle onset and variable course. Thismeans that if CVD is present in a patient with dementia, VAD islikely to be diagnosed, which might overestimate the occurrenceof this type of dementia. Furthermore, the interpretation of asingle stroke leading to dementia probably differs between centres,and may be one reason for the disparate results regarding theprevalence of vascular dementia.Table 36.7The NINDS–AIREN criteriaProbable Vascular Dementia1. Dementia2. Cerebrovascular disease(a) Focal signs consistent with strokeand(b) Relevant CVD by brain imaging:Multiple large-vessel infarctsSingle strategically placed infarctMultiple lacunes (basal ganglia, white matter)Extensive periventricular white matter lesions3. Relationship between (1) and (2):(a) Dementia onset within 3 months following stroke(b) Abrupt deterioration in cognitive functions(c) Fluctuating stepwise progressionPossible Vascular Dementia1. Dementia2. Cerebrovascular diseaseFocal signs consistent with stroke3. Absence of relationship between (1) and (2)(a) Dementia onset more than 3 months following stroke(b) Subtle onset or variable course