Diagnosis of dementia is challenging and requires both ruling out potentially treatable underlying causes and ruling in a diagnosis of dementia subtype to manage patients and suitably plan for the future.
This analysis sought to determine the appropriate use of neuroimaging during the diagnostic work-up of dementia, including indications for neuroimaging and comparative accuracy of alternative technologies.
A literature search was performed using Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid Embase, the Wiley Cochrane Library, and the Centre for Reviews and Dissemination database, for studies published between 2000 and 2013.
Data on diagnostic accuracy and impact on clinical decision making were abstracted from included studies. Quality of evidence was assessed using GRADE.
The search yielded 5,374 citations and 15 studies were included. Approximately 10% of dementia cases are potentially treatable, though less than 1% reverse partially or fully. Neither prediction rules nor clinical indications reliably select the subset of patients who will likely benefit from neuroimaging. Clinical utility is highest in ambiguous cases or where dementia may be mixed, and lowest for clinically diagnosed Alzheimer disease or clinically excluded vascular dementia. There is a lack of evidence that MRI is superior to CT in detecting a vascular component to dementia. Accuracy of structural imaging is moderate to high for discriminating different types of dementia.
There was significant heterogeneity in estimates of diagnostic accuracy, which often prohibited a statistical summary of findings. The quality of data reported by studies prohibited calculation of likelihood ratios in the present analysis. No studies from primary care were found; thus, generalizability beyond tertiary care settings may be limited.
A diagnosis of reversible dementia is rare. Imaging has the most clinical utility in cases where there is potentially mixed dementia or ambiguity as to the type of dementia despite prolonged follow-up (e.g., 2 years or more). Both CT and MRI are useful for detecting a vascular component of dementia.
Plain Language Summary
Dementia is a devastating condition of memory loss and behaviour change that affects many Canadians, especially older adults. Diagnosis is complex because symptoms can be caused by different brain diseases, such as Alzheimer disease, and in some cases by other causes such a tumour or cerebrovascular disease. Although dementia rarely improves much, an accurate diagnosis is important because it determines the treatment a patient should receive and helps patients and families understand what the future holds.
Brain imaging, using computed tomography (CT) or magnetic resonance imaging (MRI) scans, may help in the diagnosis by allowing doctors to see changes in brain structure or function that explain the dementia. Unfortunately, it is not well understood which patients will most likely benefit from a brain scan and which type of scan works best to diagnose dementia. This study reviewed the published evidence about these questions.
The study found that relying on specific symptoms to decide who should have a brain scan, rather than imaging all dementia patients, is unreliable and can miss some potentially treatable conditions. The study also found that scans have most value when doctors are uncertain as to the type of dementia despite monitoring the patient for a while (e.g., 2 years) or when the patient may have a combination of dementia types. Brain scans are often less helpful in the diagnosis of Alzheimer disease, and doctors can often use clinical assessment to rule out vascular dementia (another common type of dementia, related to cerebrovascular disease). The evidence also shows that MRI is not better than CT in detecting vascular dementia as a contributing cause. For Alzheimer disease, Creutzfeldt-Jakob disease, and clinically ambiguous dementias, both CT and MRI are highly accurate in correctly ruling out these diagnoses, but both types of scans have only low to moderate ability to correctly identify patients with any of these conditions. Importantly, the quality of the evidence available for this study was limited by considerable differences in research and analysis methods.