Dementia Diagnostics
Core Diagnostic Approach
Dementia is diagnosed when cognitive or behavioral symptoms interfere with ability to function at work or usual activities, represent a decline from previous functioning, and are not explained by delirium or major psychiatric disorder. 1
The diagnostic process requires systematic evaluation across multiple domains, with emphasis on corroborative history, structured cognitive testing, and targeted investigations to identify reversible causes.
Essential Initial Assessment
History Taking (Most Critical Component)
Obtain corroborative history from a reliable informant—this is essential and has prognostic significance. 2 Document changes in cognition, function, and behavior, distinguishing new onset symptoms from chronic or longstanding symptoms. 2
Assess specific cognitive domains affected: memory, executive function, visuospatial abilities, language functions, and personality/behavior changes. 1
Document impact on Instrumental Activities of Daily Living (IADLs): ability to manage finances, medication management, transportation, household management, cooking, and shopping. 1 This functional impairment is what differentiates dementia from mild cognitive impairment. 1
Establish onset and progression pattern—rapid onset suggests vascular or other acute causes, while gradual onset over years suggests neurodegenerative disease. 3
Review medications for drugs causing cognitive impairment. 3
Structured Cognitive Assessment Tools
Use the Mini-Mental State Examination (MMSE) as the primary tool for initial assessment and longitudinal tracking (sensitivity for moderate dementia, familiar to clinicians, used in clinical trials of cholinesterase inhibitors). 2, 1
The Montreal Cognitive Assessment (MoCA) is more sensitive for mild cognitive impairment and early dementia. 1, 3
Supplement with Clock Drawing Test for visuospatial and executive function screening. 2, 1
Use structured informant-based scales: ECog, IQCODE, Lawton IADL Scale for functional assessment. 2
Assess behavioral symptoms using NPI-Q (brief version), GDS for depression, or PHQ-9. 2
Laboratory Workup (Rule Out Reversible Causes)
Core laboratory tests are mandatory: complete blood count, comprehensive metabolic panel, thyroid function tests (TSH, free T4), vitamin B12 level, and folate level. 1, 3
Additional testing based on clinical suspicion: syphilis serology if indicated. 3
Neuroimaging (Critical Decision Points)
Anatomical neuroimaging is recommended in most situations using the following specific indications: 2
- Onset of cognitive symptoms within the past 2 years, regardless of rate of progression 2
- Unexpected and unexplained decline in cognition/function in a patient already known to have dementia 2
- Recent and significant head trauma 2
- Unexplained neurological manifestations (new onset severe headache, seizures, Babinski sign, gait disturbances) 2
- History of cancer, particularly if at risk for brain metastases 2
- Subject at risk for intracranial bleeding 2
- Symptoms compatible with normal pressure hydrocephalus 2
- Significant vascular risk factors 2
MRI is preferred over CT, especially for detecting vascular lesions, atrophy patterns, and other structural abnormalities. 2, 1, 3 If available and no contraindications exist, 3T MRI should be favored over 1.5T. 2
Recommended MRI sequences: 3D T1 volumetric sequence (with coronal reformations for hippocampal volume assessment), FLAIR, T2 (or susceptibility-weighted imaging if available), and diffusion-weighted imaging. 2
Do not routinely use advanced MR sequences (rs-FMRI, MR spectroscopy, diffusion tensor imaging, arterial spin labeling) in clinical practice—these remain research tools. 2
Special Populations and Scenarios
Subjective Cognitive Decline (Normal Cognitive Testing)
Conduct appropriate diagnostic workup to identify reversible causes and assess for psychiatric symptoms, especially depression and anxiety. 2
If corroborative history is negative, provide reassurance and offer follow-up if deterioration occurs. 2
If corroborative history is positive, schedule annual follow-ups and consider referral to memory clinic with further investigation (laboratory testing, neuroimaging, detailed neuropsychiatric testing). 2
Provide all patients with WHO recommendations for dementia prevention. 2
When to Consider Neuropsychological Testing
If clinical assessment is inconclusive (symptoms present but normal examination findings), neuropsychological testing can help determine whether dementia is present. 4
Neuropsychological testing establishes extent and severity of cognitive impairment objectively. 1
Common Pitfalls to Avoid
Do not overlook conditions that mimic or contribute to dementia: depression (pseudo-dementia), delirium, metabolic disturbances, medication effects, sleep disorders (particularly sleep apnea), and sensory deficits (hearing loss, vision loss). 1, 3
Do not rely on a single cognitive test—assessment must be multi-dimensional across cognition, function, and behavior. 2
Do not skip obtaining informant history—patient self-report alone is insufficient and may be unreliable. 2
Avoid mistaking dementia as part of normal aging—dementia always represents pathologic decline. 4
Longitudinal Monitoring and Follow-up
Schedule follow-up visits every 6-12 months for stable patients. 1, 3, 5 Patients with behavioral symptoms may need more frequent reassessment (every 3-4 months). 5
All domains must be evaluated at least annually: cognition, functional autonomy, behavioral symptoms, and caregiver burden. 2, 5 Not all domains need assessment at every visit, but annual comprehensive evaluation is mandatory. 2
Use MMSE for longitudinal cognitive tracking—it has been validated in clinical trials and is familiar to clinicians. 2 Longitudinal assessment is more meaningful than single time-point evaluations. 2
Assess caregiver burden regularly using structured scales like the Zarit Burden Interview—this is a major determinant of hospitalization and nursing home placement. 2, 5