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 0-470-84641-050bSubcortical DementiaJ. R. BurkeDuke University Medical Center, Durham, NC, USAHealth-care workers who evaluate older patients are frequentlyconfronted with individuals who they suspect have dementia.Although it is often straightforward to determine whether anindividual is demented, determining the etiology of the dementiacan be difficult. Dementia is not a single disease, but aheterogeneous complex of disorders with the common finding ofimpairment in multiple cognitive domains. Fortunately, cluesleading to a correct diagnosis can be obtained in the physical andmental status examination.A heuristic device that can aid in the evaluation of patients withdementia is to divide diseases into two categories, based onwhether the pathology is primarily cortical or subcortical 1 .Although the cortical/subcortical dichotomy has been questionedon pathologic grounds, there are clinical features that distinguishone group from the other. The prototypical cortical dementia isAlzheimer’s disease (AD). Diseases that cause subcorticaldementia include small vessel cerebrovascular disease, Parkinson’sdisease and Huntington’s disease (Table 50b.1) 2 .CLINICAL FEATURES OF SUBCORTICALDEMENTIAThe cardinal clinical features of subcortical dementia are apathy,inattention and psychomotor slowing 1,3 . Patients with subcorticaldementia typically appear apathetic. They have a blunted affect,poor personal hygiene and sloppy appearance. The patients areoften aware of their cognitive deficit but appear unconcerned. Incontrast, patients in the early stages of AD typically have normalaffect, grooming and dress. Patients with AD who are aware oftheir deficit are typically quite concerned.It is easy to become frustrated when interviewing a patient withsubcortical dementia because the patient’s inattention leads tofrequent repetition of questions by the examiner. Surprisingly,sometimes minutes after a question is asked, patients with asubcortical dementia will respond with the correct answer.Patients with AD have normal attention.Slowing is a key feature of subcortical dementia and one of themost obvious signs during the examination. Slowing occurs inmultiple areas, including cognition (thought formulation, languagegeneration and processing), sensation (processing ofstimuli) and motor performance (bradykinesia). While forcing apatient to respond quickly impairs performance in both corticaland subcortical dementia, individuals with subcortical dementiabenefit from being given more time to complete a task. Additionalresponse time does not have a similar beneficial effect for patientswith AD. The apathy, inattention and psychomotor slowing dueto subcortical dementia can be difficult to distinguish fromTable 50b.1.Causes of subcortical dementiaParkinson’s diseaseProgressive supranuclear palsyHuntington’s diseaseMultiple systems atrophyWilson’s diseaseFrontal lobe dementiaSmall vessel cerebrovascular diseaseSpinocerebellar ataxiasHydrocephalusMultiple sclerosisHIV dementiaVasculitisdepression. Patients with AD do not demonstrate psychomotorslowing, unless they are also depressed.The type of memory dysfunction differs between subcorticaland cortical dementia. Impaired registration and retrieval characterizethe memory deficit in subcortical dementia, while intactregistration and rapid forgetting are seen in AD. To testregistration and retrieval, a patient is asked to repeat a short listof words immediately after presentation (registration) and after adelay (retrieval). In subcortical dementia, the list may have to bepresented several times before all items are registered. Registrationis intact in AD patients. Patients with subcortical dementiaand AD may retrieve a similar number of items, but if presentedwith a choice, the patient with subcortical dementia candistinguish between items that were presented and items thatwere not (recognition). AD patients are unable to distinguishbetween list and non-list items. Patients with subcortical dementiaalso benefit from hints to recall items (cueing), while AD patientsdo not.Patients with subcortical dementia also frequently displaydeficits in multi-step tasks. They may perform each step of atask individually, but be unable to incorporate steps to solve theproblem. For example, a patient may be able to calculate thenumber of nickels in $1.00 and the number of nickels in $0.35, butnot the number of nickels in $1.35.Behavioral disturbance can occur with either cortical orsubcortical dementia, but apathy and depression are morecommon in the early stages of a subcortical dementia and maypredate other cognitive problems. The cortical signs, aphasia,apraxia and agnosia, are lacking in subcortical dementia andsuggest either AD or a focal process such as stroke, mass lesion orfocal degeneration (e.g. primary progressive aphasia).Motor signs, such as increased tone and bradykinesia, arecommon in subcortical dementia. Abnormal movements, such astremor, chorea or dystonia, may also occur. Posture is oftenabnormal and patients may appear stooped or extended whenstanding. Gait problems include poor initiation, small step lengthand difficulty turning. AD patients do not demonstrate motorsigns, abnormal movements or posture and gait abnormalitiesuntil the latter stages of dementia.Principles 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