Mohammed T. Abou-Saleh

DIFFERENTIAL DIAGNOSIS OF DEMENTIA 295INTRACRANIAL LESIONSAny form of intracranial mass lesion may masquerade asdementia. Cerebral tumours (primary or secondary), brain abscessor intracranial bleeds may all give rise to a dementia syndrome.Diagnosis is made through suspicion of the primary lesion andvisualization on CT scan.SUBCORTICAL DEMENTIAThis is a generic term for a particular syndrome of dementia,which has particular clinical features separating it from a corticaldementia. These include mental slowness, inertia, apathy and lossof initiative, occurring along with cognitive disturbances. Thediseases associated with subcortical dementias include Parkinson’sdisease, Huntington’s disease, progressive supranuclearpalsy, Wilson’s disease, spinocerebellar degeneration, hydrocephalusand the toxic/metabolic encephalopathies. Thestructures affected are subcortical—the basal ganglia, thalamusand the brain stem.In Parkinson’s disease, there is mental slowing, diminishedproblem solving, poor memory and a deterioration in abstraction,concept formation and word generation. Depression iscommon, as in all subcortical dementias. Cortical features (suchas aphasia, apraxia and agnosia) are absent, although someauthors claim there is a cortical dementia present, probably dueto coexisting Alzheimer’s disease. The diagnosis of Parkinson’sdisease is essentially a clinical one and physical manifestationsof the disease will generally be present when the dementia isapparent.Huntington’s disease is characterized by choreiform movementsand associated with autosomal dominant transmission. Personalitychanges, irritability and apathy are the first changes andpredate the chorea. The dementia appears soon after themovement disorder becomes apparent, characterized by memorydisturbance (impaired recall of both recent and remote memories),slowing, failure to initiate cognitions (especially those required inplanning) and impaired concentration and judgement 26 . Althoughdementia without chorea has been described, it is very rare andthe diagnosis of Huntington’s disease is usually suspected prior tothe onset of dementia 18 .Pseudobulbar palsy, rigidity (more pronounced in the neck andtrunk) and paralysis of vertical gaze (downward gaze lost first,followed by failure of upward gaze) are hallmarks of progressivesupranuclear palsy, and the associated dementia is classicallysubcortical (indeed, the original description of subcorticaldementia was based on the dementia of progressive supranuclearpalsy). Speech is disrupted (e.g. dysarthria and hypophonia) butaphasia is absent. The clinical features are such that the diagnosiswill often be suspected and, although it may be confused withParkinson’s disease, the characteristic tremor of the latter isabsent.Other conditions resulting in subcortical dementias occurrarely and are of limited relevance to old age psychiatry. Theamyotrophic lateral sclerosis–Parkinson–dementia complex ofGuam is rare outside the Chonorro population of theWestern Pacific, the dementia being profound and characterizedby features of decreased memory, apathy and slowness;cerebellar degenerations are associated features of subcorticaldementia but the cerebellar dysfunction is usually theprominent feature; Wilson’s disease and Friedreich’s ataxiaare associated with dementia, but are confined to childrenand young adults.NORMAL PRESSURE HYDROCEPHALUSA potentially treatable cause for a dementia syndrome ishydrocephalus, the most widely cited being normal pressurehydrocephalus. The classical clinical triad consists of gaitdisturbance (ranging from mild clumsiness to akinesis), incontinence(almost always urinary incontinence, occurring late in theillness) and dementia (impaired memory, disorientation andmental slowing). The diagnosis is made by radiological examination(CT scan shows marked enlargement of the ventricleswith relatively normal cortical sulci, and isotope cisternographyshows obstruction to the flow over the cortex). A ventricularshunt to divert cerebrospinal fluid is the appropriate treatmentbut not all cases improve, even when the classical clinical pictureis present.PICK’S DISEASEPersonality changes and mood disorders (ranging from depressionto elation) occur first, with coarsening of affect andantisocial behaviour. Impaired judgement occurs, with loss ofinsight. Aphasia and circumlocution occur early. Memory isrelatively unimpaired until the later stages of the disease, as ispraxic function. The Kluver–Bucy syndrome has been describedearly in the illness, but this also appears in Alzheimer’sdisease 19 . Extrapyramidal signs appear late in the illness butthe clinical picture is unlikely to be confused with Parkinson’sdisease. Seizures are said to be less common than inAlzheimer’s disease and CT scan shows frontal and temporallobe atrophy, rather than the generalized shrinkage seen inAlzheimer’s disease. The diagnosis is made on the basis of thecharacteristic onset of personality changes before the onset ofdementia.DEMENTIA OF THE FRONTAL LOBE TYPERecently, descriptions have emerged of a form of dementia thatappears to affect the frontal lobes and is defined in terms ofclinical presentation (personality change, speech impairmentand relative preservation of visuospatial functions), neuropsychologicalfunction (frontal lobe syndrome) and blood flowstudies (diminished frontal lobe blood flow on single-photonemission tomography) 20–22 . There is frontal and temporal lobeatrophy and, while the condition resembles Pick’s disease, thecharacteristic neuronal inclusion bodies are absent. Diagnosis ismade on clinical grounds but confirmation usually has to awaitautopsy.DEMENTIA OF LEWY BODY TYPEThis has been described with increasing frequency and isconsidered to be amongst the commonest forms of primarydementia 23 . The relationship of this syndrome to Parkinson’sdisease is uncertain, but the clinical picture of parkinsonianfeatures, hallucinosis and episodes of confusion should raise thediagnostic possibility.TOXIC-METABOLIC ABNORMALITIESGenerally, these are readily identifiable by the primary cause forthe syndrome (such as anoxia, renal or hepatic failure) and thesymptomatology produced is more often identifiable as anencephalopathy rather than a dementia syndrome. There are a