Persons with cognitive impairment are frequently excluded from research, often without rationale or mention of exclusion as a limitation or any discussion of its potential effect on the evidence base in geriatrics. When necessary, exclusion should be done thoughtfully and with awareness that this may reduce the clinical utility of study findings.

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Background-Accurate assessment of dementia's impact on health care utilization and costs requires separation of the effects of comorbid conditions, often poorly accounted for in existing claims-based studies.

OBJECTIVES To determine how often neuroimaging confirms, clarifies, or contradicts initial diagnoses of late life cognitive disorders. DESIGN Retrospective case review. SETTING An outpatient clinic specializing in memory disorders. PARTICIPANTS 193 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 (non-contrast MRI) and perfusion (Tc-99m ECD SPECT) 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 1, and was abnormal/not diagnostic in 7. In dementia 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) than in other clinical groups (68% vs. 22%, χ2 = 22.8 p < 0.001). 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 >80% of patients while < 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, while 46% of complex clinical differential diagnoses appeared to reflect a single causal pattern. Further work is needed to determine whether refinement of clinical diagnoses by specialized neuroimaging improves clinical decision-making and patient outcomes.

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