Magnetic resonance imaging in dementia

Dementia is a clinical syndrome that has many causes. Structural neuroimaging is needed to refine differential diagnosis and identify comorbidity. Excluding structural lesions remains an important indication for either a CT or MR scan in an individual with cognitive decline, particularly if the presentation is in any way unusual. The ability of CT, if done appropriately with negative angulation and thin slices, and MRI to detect even subtle medial temporal lobe atrophy helps to diagnose Alzheimer's disease and differentiate it from normal aging and non-dementia (i.e. depression) but does not rule out other dementias. Absence may indicate dementia with Lewy bodies if fitting with the clinical suspicion. The sensitivity of MRI to detect vascular pathology aids tremendously to the distinction between Alzheimer's disease and vascular dementia, but has also learnt that overlap syndromes between the two conditions exist. Definite progress is being made in distinguishing normal aging from neurodegeneration using serial scans. The pattern of atrophy may indicate a focal dementia rather than Alzheimer's disease. Clinically useful measures that distinguish the different neurodegenerative disorders from each other at an early stage are still awaited. MRI is increasingly being used to predict incipient dementia in subjects with mild cognitive impairment and as such the presence of medial temporal lobe atrophy has more predictive value for Alzheimer's disease than any other measure. Imaging research is also likely to focus on measuring progression and detecting therapeutic effect. Hence, MRI is already being used in clinical trials in mild cognitive impairment, Alzheimer's disease and vascular dementia. MRI is increasingly seen as an essential investigation in dementia. Unless and until novel biomarkers are found that can reliably detect and track the underlying pathological processes in the different dementias, MRI will continue to play an important role in the diagnosis of patients with dementia and in research into treatments.