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The use of CT scanning in dementia: a systematic review |
Foster G R, Scott D A, Payne S |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The use of CT scanning in dementia.
Study population Male and female patients above and below 65 years of age with newly-diagnosed dementia without a theoretically treatable condition.
Setting Hospital. The study was carried out in Scotland, UK.
Dates to which data relate The effectiveness data were derived from studies previously published between 1972 and 1996. The dates during which resource use data were collected were 1996-7. The price year was not reported.
Source of effectiveness data Effectiveness data were derived from a systematic review of published studies plus estimates made by the authors.
Modelling A decision tree (spreadsheet) was used to model costs and benefits of the screening strategies. This is available on request from the authors.
Outcomes assessed in the review The following outcomes were assessed in the review: prevalence of dementia, prevalence of reversible dementia, proportion of reversible dementias detectable by CT, the occurrence of normal pressure hydrocephalus (NPH), brain tumours and chronic subdural haematomas (SDH), the proportion of all dementia with lesions detectable by CT, the proportion of CT detectable reversibles, SDH or for NPH, the number of life years gained by tumour treatment, and the number of life years gained with and without SDH operation or NPH operation.
Study designs and other criteria for inclusion in the review Observational studies were included since few clinical trials were available.
Sources searched to identify primary studies The MEDLINE and Embase databases and references from personal contacts were searched. Reference lists of all useful papers obtained were also used.
Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Not stated. Summary statistics from each study were used.
Number of primary studies included 21 studies were included.
Methods of combining primary studies Most effectiveness estimates were not combined, although on a few occasions weighted averages were used. The data are largely based on Clarfield's meta-analysis (ref. 12), supplemented by other studies (amounting to 4,800 patients).
Investigation of differences between primary studies Results of the review The following are baseline values but the authors also provided best case and worst case values in the paper (used in the sensitivity analyses). The prevalence of dementia was 9.3%. The proportion of reversible dementias and the proportion of reversible dementias detectable by CT were 13.7% and 27.5%, respectively. NPH occurs in less than 2% of dementia cases. Brain tumours occur in 1 to 4% of cases. SDH occurs in 0.4% of demented patients. The proportion of all dementia with lesions detectable by CT was 6.6%. The proportion of CT detectable reversibles due to tumour, SDH or NPH was 53.36, 11.13, and 35.51, respectively. The probabilities of mortality with surgery for tumour, for SDH and for NPH were 0.05 each. The probabilities of improvement with surgery for tumours, SDH, and NPH were 0.18, 0.8, and 0.2, respectively. The number of life years gained by tumour treatment was 6 months. The life years gained after improvement from SDH operation were 100% (of 16 years), if untreated SDH 25%, or after failure to improve from SDH operation were 25%. The life years gained after improvement from NPH operation, if untreated NDH, or after failure to improve from NDH operation are 75%, of 16 years each. These data formed the principal effectiveness/outcome parameters used in the model.
Methods used to derive estimates of effectiveness Where data were not available in the literature, the authors estimated some variables.
Estimates of effectiveness and key assumptions The proportion of reversible dementias detectable by CT was 35% (best case) and 10% (worst case). The probability of mortality with surgery for tumour was 0.05 (best case = 0.02, worst case = 0.1).
Measure of benefits used in the economic analysis Quality-adjusted life years (QALYs) were used as the measure of benefits. The authors adopted the quality of life values used by Simon and Lubin, which were based on their assessment of quality of life for demented subjects.
Direct costs Costs were not discounted given that only screening and initial treatment costs were included. Direct costs included costs of the scan, capital charges, transport and community costs. The quantity/cost boundary adopted was that of the health service. The estimation of quantities was based on actual data. Cost estimates were derived from the Royal Infirmary of Edinburgh NHS Trust and Dundee Teaching Hospitals NHS Trust. The price year was not reported.
Statistical analysis of costs Sensitivity analysis Multiple one-way sensitivity analyses were conducted on all variables used in the model. The ranges chosen were derived from the literature or in a small minority of cases, by estimates. The impact on the results was also investigated over a range of prevalence values.
Estimated benefits used in the economic analysis A strategy of screening all patients with dementia and only treating those with SDH generated 178 QALYs. A strategy of screening all patients with dementia and only treating those with SDH and NPH generated 174 QALYs. A strategy of screening all patients with dementia and only treating those with SDH and tumours generated 217 QALYs.
Cost results The costs associated with screening all patients with dementia and only treating those with SDH amounted to 2,517.329. The costs associated with screening all patients with dementia and only treating those with SDH and NPH amounted to 2,997.639. The costs associated with screening all patients with dementia and only treating those with SDH and tumours amounted to 4,243.857.
Synthesis of costs and benefits A strategy of screening all patients with dementia and only treating those with SDH had a cost-utility of 14,171/QALY. A strategy of screening all patients with dementia and only treating those with SDH and NPH had a cost-utility of 17,238/QALY. A strategy of screening all patients with dementia and only treating those with SDH and tumours had a cost-utility of 19,983/QALY. The sensitivity analyses revealed that the results were most sensitive to the proportion of all cases of dementia that are reversible, the proportion of those reversible cases that can actually be detected by CT scanning, the future life span of the patients presenting for screening, and the cost of each CT scan. In terms of prevalence variations, if this was assumed to be 15% the total cost to the NHS would rise to 4,060,208 per annum, whilst a prevalence rate of 6.5% would result in a total cost of 1,759,423. The results of all the sensitivity analyses are comprehensively and clearly reported in the paper.
Authors' conclusions CT scanning appears cost-effective in dementia patient aged under 65 years. However, it should be undertaken selectively in more elderly patients. Surgical treatment of NPH may reduce quality-adjusted survival and should only be undertaken within clinical trials.
CRD COMMENTARY - Selection of comparators The rationale for the choice of the comparator (no screening) was clear. In terms of other comparators, however, the authors did not consider other available screening technologies such as magnetic resonance imaging, single photon emission computed tomography, or positron emission tomography.
Validity of estimate of measure of effectiveness The principal input parameters for the model were derived from a well conducted and systematic review (one study being a large-scale meta analysis), although it should be noted that some values were estimated. Additionally, all parameters were tested over plausible ranges in the sensitivity analyses, with clear and comprehensive reporting. Therefore the effectiveness data should have high validity. The results do not seem to have been presented selectively. The authors acknowledged, however, that the model did not take into account the harm done to elderly patients who have to undergo a CT scan as a result of false positive results and any subsequent tests or treatment.
Validity of estimate of measure of benefit Quality of life estimates were specifically derived for demented patients and therefore the validity of the results is likely to be high.
Validity of estimate of costs The costs were derived from what appear to have been reliable sources and were also tested in the sensitivity analyses over plausible ranges. The authors, however, limited their analysis to direct costs, and opportunity costs of CT scans were not considered. It should also be noted that treatment costs for those patients for whom treatment was unsuccessful were not included. The cost estimates are likely to be specific to the Scottish setting although the sensitivity analyses conducted tend to increase the generalisability of the results. A good feature of the cost results was that the total costs of the screening programme under various scenarios were presented, thus assisting decision makers in evaluating the likely impact on healthcare budgets.
Other issues The robustness of the results was appropriately tested using sensitivity analyses. Decision makers should be aware, however, that, in the absence of screening by CT scanning, 50% of treatable structural lesions are likely to be detected in normal practice, thereby decreasing the marginal benefit of CT scanning. The authors provided a useful discussion of the potential cost consequences in caring for the elderly with dementia, and the likely impact of scanning and treating. The generalisability of the results to other settings or countries was not specifically discussed (although they are of clear relevance to the NHS). Cmparisons with other studies were not provided.
Implications of the study The authors recommend that CT scanning should be limited to those patients for whom it is clearly indicated by the signs and symptoms of the illness. A suggested strategy is CT scan demented patients only when: (a) aged under 65, OR (b) aged 65 and over AND onset < 1 year OR atypical presentation OR rapid unexplained deterioration OR unexplained focal neurological signs or symptoms OR history of recent (before onset) head injury OR urinary incontinence or gait ataxia early in the illness.
Bibliographic details Foster G R, Scott D A, Payne S. The use of CT scanning in dementia: a systematic review. International Journal of Technology Assessment in Health Care 1999; 15(2): 406-423 Indexing Status Subject indexing assigned by NLM MeSH Age Factors; Aged; Aged, 80 and over; Cost-Benefit Analysis; Dementia /epidemiology /etiology /radiography /surgery; Humans; Incidence; Mass Screening /economics /methods; Middle Aged; Models, Econometric; Patient Selection; Prevalence; Quality-Adjusted Life Years; Scotland /epidemiology; State Medicine /economics; Survival Analysis; Tomography, X-Ray Computed /economics /standards; Treatment Outcome AccessionNumber 21999008259 Date bibliographic record published 31/12/1999 Date abstract record published 31/12/1999 |
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