Impaired abstract thinking may discriminate between normal aging and vascular mild cognitive impairment

O pensamento abstrato comprometido pode diferenciar o envelhecimento normal do comprometimento cognitivo leve vascular

ARTICLE

Impaired abstract thinking may discriminate between normal aging and vascular mild cognitive impairment

O pensamento abstrato comprometido pode diferenciar o envelhecimento normal do comprometimento cognitivo leve vascular

Felipe Kenji Sudo^I; Gilberto Sousa Alves^I; Carlos Eduardo de Oliveira Alves^I; Maria Elisa Lanna^II; Letice Ericeira-Valente^I; Denise Madeira Moreira^III; Eliasz Engelhardt^II; Jerson Laks^{I, IV}

^IPsychiatry Institute,Federal University Rio de Janeiro, Rio de Janeiro RJ, Brazil

^IINeurology Institute Deolindo Couto, Federal University Rio de Janeiro, Rio de Janeiro RJ, Brazil

^IIIPró-Cardíaco Hospital, Radiology Department, Rio de Janeiro RJ, Brazil

^IVState University Rio de Janeiro, Rio de Janeiro RJ, Brazil

^{Correspondence}

ABSTRACT

OBJECTIVE: Cerebrovascular disease (CVD) is associated with cognitive deficits. This cross-sectional study examines differences among healthy elderly controls and patients with vascular mild cognitive impairment (VaMCI) and vascular dementia (VaD) in performances on CAMCOG subscales.

METHOD: Elderly individuals (n=61) were divided into 3 groups, according to cognitive and neuroimaging status: 16 controls, 20 VaMCI and 25 VaD. VaMCI and VaD individuals scored over 4 points on the Hachinski Ischemic Scale.

RESULTS: Significant differences in total CAMCOG scores were observed across the three groups (p<0.001). VaD subjects performed worse than those with VaMCI in most CAMCOG subscales (p<0.001). All subscales showed differences between controls and VaD (p<0.001). Performance on abstract thinking showed difference between VaMCI and controls (p<0.001).

CONCLUSION: CAMCOG discriminated controls from VaMCI and VaD. Assessment of abstract thinking may be useful as a screening item for diagnosis of VaMCI.

Key words: CAMCOG, elderly, mild cognitive impairment, vascular dementia, cerebrovascular disease, abstract thinking.

RESUMO

OBJETIVO: A doença cerebrovascular (DCV) associa-se a déficits cognitivos. Este estudo transversal objetiva examinar diferenças entre controles saudáveis idosos e pacientes com comprometimento cognitivo leve vascular (CCLV) e demência vascular (DV) nas subescalas do CAMCOG.

MÉTODO: Indivíduos idosos (n=61) foram divididos em 3 grupos, de acordo com o perfil cognitivo e com a neuroimagem: 16 controles, 20 CCLV e 25 DV. Pacientes com CCLV e DV pontuaram acima de 4 pontos no Escore Isquêmico de Hachinski.

RESULTADOS: Diferenças significativas foram observadas entre os três grupos no resultado final do CAMCOG. Pacientes com DV obtiveram escores inferiores àqueles dos indivíduos com CCLV em quase todas as subescalas. Todas as subescalas mostraram diferenças entre DV e controles. O desempenho no item pensamento abstrato mostrou diferenças entre CCLV e controles.

CONCLUSÃO: O CAMCOG diferenciou controles de pacientes com CCLV e DV. A avaliação do pensamento abstrato pode ser útil para discriminar CCLV de controles.

Palavras-chave: CAMCOG, idosos, comprometimento cognitivo leve, demência vascular, doença cerebrovascular, pensamento abstrato.

Vascular mild cognitive impairment (VaMCI) can be defined as a cognitive impairment of vascular etiology that does not fulfill criteria for dementia¹. It has been proposed that vascular-related cognitive impairment exists throughout a continuum comprising VaMCI, vascular cognitive impairment no-dementia (Va-CIND) and vascular dementia (VaD)². In a sample of cerebrovascular disease (CVD) patients with cognitive difficulties, Wentzel et al.³ reported a 50% rate of conversion to dementia over a five-year period. The early detection of VaMCI may allow therapeutic intervention designed to halt or delay the progression of vascular lesions so as to prevent the conversion to dementia^4,5. Presently, the diagnosis of mild cognitive impairment (MCI) requires improvement in the sensitivity of conventional screening tests for dementia, since the rate of false-negative results is usually high for those individuals^6,7. Studies attempting to increase such sensitivity have shown that a combination of different screening tests provides higher diagnostic accuracy compared to each test individually^8,9. Diniz et al.⁷ analyzed Mini-Mental State Examination (MMSE) subtests in a sample of MCI subjects and managed to identify distinct profiles of cognitive deficits among the MCI subtypes. A higher rate of patients with MCI could be identified when the item scores were analyzed, which was not possible when only MMSE final scores were considered. ROC curve analyses were performed to determinate cutoff scores in the Cambridge Cognitive Examination (CAMCOG) for MCI patients, but discrimination between MCI subjects and controls with this method showed low accuracy¹⁰.

It was suggested that some cognitive domains might be specifically impaired in MCI subjects and these aspects could serve as differential markers to distinguish this condition from normal aging. Rodríguez et al. found that individuals diagnosed as MCI performed significantly worse than controls in CAMCOG subtests assessing various areas, with higher significance levels corresponding to the variables memory, abstract thinking and executive function¹¹. In a previous study, Erkinjuntii et al. observed impairment in memory, conceptual functions and arithmetical skills in a sample of individuals presenting age-related cognitive changes¹². Recently, one other study showed that memory, constructive ability and abstract thinking were particularly impaired in MCI individuals compared to controls¹³.

The purpose of this study is to evaluate the performance of VaMCI patients in comparison to cognitively unimpaired controls and VaD individuals on the CAMCOG tasks. We hypothesized that characterization of cognitive deficits using CAMCOG subtests may provide an increase in sensitivity in the screening for VaMCI, in addition to total test score. Furthermore, we intended to verify if cognitive domains specially impaired in MCI individuals, such as memory, abstract thinking and executive function, could also serve as cognitive markers to diagnosis of VaMCI.

METHOD

Participants

Sixty-one elderly outpatients (mean age: 73.49±7.24 years; 68.85% female; mean education level: 6.86±4.57 years) were consecutively assessed at the Centre for Alzheimer Disease and Related Disorders (CDA), Federal University of Rio de Janeiro (UFRJ), Brazil, between July 2006 and October 2008. The sample comprised both subjects who spontaneously demanded medical assistance due to cognitive complaints and those referred from other clinics. Cognitive unimpaired controls were volunteers recruited from several sources who accepted invitation to participate in the study. Informed consent was obtained from participants or from a family member responsible prior to enrolment. This study is a branch of a larger project on vascular cognitive disorder, approved by the Ethics Committee of IPUB-UFRJ.

Clinical and neuropsychological assessment

Patients and controls were examined by a multidisciplinary team, comprising psychiatrists, neurologists, one radiologist and one neuropsychologist. An interview with patient and caregiver was performed and those who had history of alcohol or drug abuse, psychiatric disorders (e.g. schizophrenia, bipolar mood disorder or lifetime depressive disorder), non-corrected visual or auditory disorders, exposure to neurotoxic substances and cranioencephalic traumatism were excluded from the study. The cognitive assessment included the Cambridge Cognitive Examination (CAMCOG)¹⁴, Mini-Mental State Examination (MMSE)¹⁵, semantic verbal fluency (category animals)^16,17, Trail Making Tests (TMT) A and B¹⁸ and the 12-item-Boston Naming Test¹⁹. Behavioral evaluation was assessed by the Neuropsychiatric Inventory (NPI)^20,21. Depressive symptoms were measured with Cornell Depression Scale^22,23. Pfeffer's Functional Activities Questionnaire (FAQ)²⁴ was administered to informants (a close relative or a caregiver) in order to identify evidence of functional decline. Risk factors for CVD were scored using Hachinski Ischemic Score (HIS)²⁵. Individuals were rated according to severity of cognitive deficits on the Clinical Dementia Rating scale (CDR)^26,27. Laboratory tests were carried out to rule out reversible causes of cognitive decline, such as nutritional deficiencies, syphilis or diseases of the thyroid. All subjects underwent MRI scan of the brain.

The inclusion of VaD patients was based on the Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV)²⁸ and the National Institute of Neurological Disorders and Stroke and Association Internationale pour la Recherché et l'Enseignement en Neurosciences (NINDS-AIREN)²⁹ criteria for probable VaD.

The diagnosis of MCI was made according to Petersen's criteria³⁰. MCI individuals scored below 4 points on Pfeffer's FAQ and this cutoff value was adopted to show functional activities largely preserved. Furthermore, VaMCI patients were identified as those who obtained above 4 points on the HIS, showing high risk-factors for CVD, which were correlated with vascular subcortical lesions and absence of significant cortical atrophy in MRI images.

The control group was submitted to the same procedures described above. Subjects in this group did not present evidence of cognitive and functional impairment and had no or not significant neuroimaging abnormalities, such as vascular subcortical lesions or cortical atrophy not correspondent to the expected for normal aging. Also, they had no history of major psychiatric disorders or substance-abuse.

Statistical analyses

Statistical analyses were made using SPSS for Windows version 11.5. Univariate Analysis of Variance (ANOVA) was carried out to assess significant mean differences for "Age" and "Educational Level", followed by post-hoc Bonferroni analysis. Pearson's Chi-square analysis was performed to evaluate differences in the distribution of gender among the three groups. Analysis of covariance (ANCOVA) was performed to control for the potential confounding effects of schooling on cognitive variables.

RESULTS

Table 1 illustrates the sociodemographic data of individuals among the three groups. Proportion of male and female subjects did not differ significantly among the groups. The control group showed a higher educational level when compared to VaD patients. This is depicted in Figure.

Results of the cognitive and behavioral evaluations are displayed in Table 2. Multiple comparison tests showed that VaD patients had worse performances in HIS, Cornell Depression Scale, changes in TMT A and TMT B (both time and errors) and Boston Naming Test as compared to controls. In comparison to controls and VaMCI, VaD individuals had worse scores in NPI, FAQ, TMT A and Verbal Fluency.

Multivariate analyses indicated that the three groups differed significantly in CAMCOG final scores. Analyses of scores in the CAMCOG subtests demonstrated that abstract thinking was the only item that showed differences among the three groups. Mean scores in orientation, language, memory, attention and praxis indicated significant differences between VaMCI persons and those with VaD, and also between controls and VaD individuals. Visual and spatial perception, as well as calculation showed significant differences only between controls and VaD subjects. These data are shown in Table 3.

DISCUSSION

The present study showed that VaMCI and controls had significantly different performances in regards to the CAMCOG total scores (p<0.001). Another interesting finding was that impairment in abstract thinking was present in VaMCI but not in controls. Other subtests, such as orientation, language, memory, attention and praxis showed accuracy in separating VaMCI subjects from VaD individuals (p<0.001), whereas tactile and visual perception and calculation could only identify VaD patients from controls (p<0.001). MMSE failed in discriminating controls from VaMCI. VaMCI subjects and controls had similar overall performances on cognitive and behavioral evaluation, as depicted in Table 2.

Nunes et al.¹⁰ showed that CAMCOG presented a sensitivity of 64% and a specificity of 88%. One previous study, however, which explored psychometric properties (reliability, discriminative capacity and factorial structure) of the CAMCOG, found an excellent reliability of the individual subscales and high levels of sensitivity and specificity of the instrument in differentiating between demented and non-demented individuals³¹.

This study shows some limitations that should be outlined and commented. Significant differences were found in scores on Cornell Depression Scale between VaD individuals and controls. Depression is a common condition observed in patients with CVD and it can be related to poorer performances in cognitive assessment, acting as a confounding factor to cognitive deficits primarily associated to dementia^32,33. Therefore, our results in cognitive evaluation of VaD patients should be considered with care. On the other hand, no significant difference in assessment of depressive symptoms was found between VaMCI subjects and controls, indicating that comparison of cognitive performances among those groups did not suffer this confounding effect. Schooling was lower in VaD patients compared to controls, which may also lead to difficulties in distinguishing cognitive impairment from low scores in cognitive assessment associated to educational level.

Moreover, our results do not agree with some studies wherein the cognitive tests of MCI patients showed a ceiling effect, thus not being able to accurately recognize patients from controls. A possible explanation for the absence of a ceiling-effect could be the small sample, and similar studies with a larger sample should be performed. A great heterogeneity of individuals classified as MCI following Petersen's criteria has been described in many studies³⁴, and our findings may have been influenced by this limitation. Characterization of MCI may vary according to the different neuropsychological instruments employed³⁵, which may also explain the variation of cognitive profiles of MCI among the studies. Differently from the studies mentioned previously, our sample is constituted by individuals with vascular-related cognitive deficits, instead of those associated to neurodegeneration, and this aspect may be related to the particularities of the results of this study. Furthermore, our sample was recruited at the Centre for Alzheimer Disease and Related Disorders (CDA-UFRJ), and population-based studies, as well as studies with a larger sample are needed in order to replicate the results.

The assessment of abstract thinking requires the ability of establishing similarities between objects. This capacity has been related to frontal lobe functioning³⁵. Impairment of abstract thinking has been considered one important cognitive marker in the discrimination between MCI and normal aging^11,13 and, since evaluation can be considered simple, it may be a helpful item for clinical assessment of aged individuals with suspect of VaMCI. In conclusion, we propose that the analyses of each CAMCOG subtest, with emphasis on abstract thinking task, could be important as a screening item for early diagnosis of cognitive deficits in patients with high risk for CVD.

Received 14 September 2009

Received in final form 12 November 2009

Accepted 22 November 2009

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Publication Dates

• Publication in this collection
  28 Apr 2010
• Date of issue
  Apr 2010

History

• Accepted
  22 Nov 2009
• Reviewed
  12 Nov 2009
• Received
  14 Sept 2009