Neuroimaging in the clinical diagnosis of dementia: observations from a memory disorders clinic

Abstract

Objectives: To determine how often neuroimaging confirms, clarifies, or contradicts initial diagnoses of late-life cognitive disorders.

Design: Retrospective case review.

Setting: Outpatient clinic specializing in memory disorders.

Participants: One hundred ninety-three consecutively referred cognitively impaired patients.

Measurements: Diagnoses using research criteria were developed for each patient at the first visit and ranged from cognitive impairment without dementia to dementias of single, complex, or indeterminate etiology. Structural (noncontrast magnetic resonance imaging) and perfusion (technetium-99m ethyl cysteine dimer single photon emission computed tomography) images were categorized together as normal, suggestive of specific diseases, or abnormal/not diagnostic.

Results: When a single neurodegenerative disease was suspected clinically (n=94), imaging confirmed the diagnosis in 50, contradicted the diagnosis in 32, and was abnormal/not diagnostic in 12. When more than one neurodegenerative etiology was clinically suspected (n=21), imaging assigned a single diagnosis in 13 and only cerebrovascular disease in one and was abnormal/not diagnostic in seven. In dementia not otherwise specified (NOS) (n=33), imaging suggested a specific etiology in 23 and was abnormal/not diagnostic in 10. Abnormal/not diagnostic images were more common in cognitive disorder NOS (n=25, 68%) than in other clinical groups (22%, chi-square=22.8 P<.001). Neuroimaging indicators of cerebrovascular disease were common (60% prevalence) but not predicted by the presence of vascular risk factors alone.

Conclusion: Overall, neuroimaging confirmed, clarified, or contradicted the initial clinical diagnosis in more than 80% of patients, whereas fewer than 20% had abnormal/not diagnostic patterns. Imaging suggested a complex dementia etiology in 21% of cases clinically thought to be caused by a single process, whereas 46% of complex clinical differential diagnoses appeared to reflect a single causal pattern. Further work is needed to determine whether refinement of clinical diagnoses using specialized neuroimaging improves clinical decision-making and patient outcomes.