Cognitive dysfunction in older subjects with diabetes mellitus: impact on diabetes self-management and use of care services

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Abstract

Objective: To determine whether cognitive impairment is associated with changes in self-care behaviour and use of health and social services in older subjects with diabetes mellitus. Research design and methods: This was a community based, case-control study of subjects registered with general practices participating in the All Wales Research into Elderly (AWARE) Diabetes Study. The 396 patients aged 65 years or older with known diabetes mellitus were compared with 393 age- and sex-matched, non-diabetic controls. Adjusted odds ratio estimates of normal performance on Mini-Mental State Examination (MMSE) and Clock Drawing Test (numbers and hands) were determined. Information on self-care behaviours and use of services was obtained. Results: A total of 283 (71%) diabetic subjects scored 24 or more on MMSE, compared with 323 (88%) of controls (OR 0.54, P<0.0005). The mean (S.D.) scores were 24.5 (5.1) and 25.7 (4.3), respectively (difference between means 1.22; 95% CI 0.56, 1.88; P<0.001). Clock testing demonstrated that 257 (65%) and 286 (72%) diabetic subjects correctly placed the numbers and hands, respectively, compared with 299 (76%) and 329 (84%) of controls (OR 0.59, P<0.001 and P<0.52, P<0.0005, respectively). Both test scores declined with increasing age, earlier school leaving age and deteriorating visual acuity. Of other variables examined, only need for oral hypoglycaemic drugs or insulin, history of stroke, dementia or Parkinson's disease and symptoms of autonomic neuropathy significantly impaired one or more cognitive test scores. The odds ratios (95% CI) for normal cognitive test results in subjects with diabetes after adjusting for all significant variables was 0.74 (0.56, 0.97), P=0.029 for MMSE scores and 0.63 (0.44, 0.93), P=0.019, and 0.58 (0.38, 0.89), P=0.013, for the numbers and hands parts of the clock test, respectively. In comparison with diabetic subjects with no evidence of cognitive impairment, diabetic subjects with an MMSE score <23 were significantly less likely to be involved in diabetes self-care (P<0.001) and diabetes monitoring (P<0.001). A low MMSE score was also significantly associated with higher hospitalisation in the previous year (P=0.001), reduced ADL (activities of daily living) ability (P<0.001) and increased need for assistance in personal care (P=0.001). Conclusions: Elderly subjects with predominantly Type 2 diabetes mellitus display significant excess of cognitive dysfunction, associated with poorer ability in diabetes self-care and greater dependency. Routine screening of cognition in older subjects with diabetes is recommended.

Introduction

Several studies have suggested that poor cognitive performance may be associated with Type 2 diabetes mellitus although an investigation of the aetiology or nature of this impairment or its clinical significance was not undertaken [1], [2], [3]. However, recent population-based cohort studies have suggested that older subjects with diabetes may be at increased risk of dementia [4], [5] whilst impaired glucose tolerance has also been linked to poor cognitive performance [6], [7].

In contrast, several studies of cognitive performance have reported little or no differences in subjects with Type 2 diabetes compared with control non-diabetic subjects [8], [9]. A preliminary study by our group using a neuropsychological battery of tests has also cast doubt on this association [10]. In this latter study, the lack of difference may have been due to a small group sample size (<30 subjects), and relatively good metabolic control (including control of blood pressure in those with hypertension) of study subjects with Type 2 diabetes. A recent community-based study with a more representative group of subjects found that those with known diabetes were more likely than non-diabetic subjects to have a low mental state examination score [11], and a critical review of 19 controlled studies concluded that sufficient evidence exists to link cognitive dysfunction with Type 2 diabetes [12].

Irrespective of the cause of cognitive impairment, its presence is likely to lead to changes in the ability of individual patients with diabetes to self-manage. This may compromise their empowerment role and co-operation with educational approaches which are important keys to effective management [13].

The purpose of the present study was, therefore, to determine whether diabetes mellitus (predominantly Type 2) in older subjects is associated with cognitive impairment of clinical importance which is likely to have an impact on day to day functioning and diabetes self-management. We used two simple but well-validated screening measures in a large community-based cohort of British subjects.

Section snippets

Research design

Subjects were recruited as part of the All Wales Research into Elderly (AWARE) Diabetes Study. This used a case control design to comprehensively evaluate morbidity, disability and quality of life and organisation of health care for elderly patients with diabetes mellitus living in both urban and rural sites in Wales.

The cohort of patients identified were aged 65 years or over and included all known cases of diabetes mellitus [14] in a sample of general practices in North, South and Mid-Wales.

Study population

Of the 571 subjects with diabetes mellitus, initially identified from general practice records, 96 were found to be ineligible (mainly because they were deceased, had moved out of the area or diagnosis of diabetes was not confirmed). Of the 475 eligible subjects, 16 were too ill to be interviewed, 49 refused consent, seven could not be contacted despite repeated efforts and seven could not attempt cognitive assessments because of severe visual impairment. Thus 396 (83%) of the eligible subjects

Discussion

Compared with an age- and sex-matched group of non-diabetic control subjects, this cross-sectional general practice study demonstrated the presence of greater prevalence of cognitive dysfunction (based on two simple cognitive screening tests) in an elderly group of subjects with predominantly Type 2 diabetes. A substantial excess of diabetic subjects had cognitive scores compatible with moderate to severe dementia. Evidence of significant underperformance in both measures of cognition in the

Acknowledgements

This study was supported by a grant from the Department of Health funded via the Welsh Office. Our special gratitude goes to Catherine Davies, Christine Corbett and Carys Brisbane for their commitment to the project, to the willing and supportive general practitioners and to Heather Copeland for help with data entry.

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