Diagnosis and Evaluation of Dementia

Introduction to Diagnosis

The diagnosis of dementia is a clinical diagnosis that requires a physician's judgment and cannot be confirmed by a single laboratory test, according to the American College of Radiology 1
A comprehensive dementia evaluation must include standardized cognitive assessment, thorough history collection from both patient and informant, physical examination focused on neurological findings, basic laboratory testing, and appropriate neuroimaging to accurately diagnose the cognitive-behavioral syndrome and its underlying cause(s) 2

The American College of Radiology recommends a comprehensive clinical evaluation, including a detailed medical history, standardized cognitive assessment, and physical and neurological examination, to diagnose dementia 1
Obtain detailed cognitive, functional, behavioral, and mood symptoms with timeline of onset and progression from patients with dementia and their informants 2, 3
Document specific changes in memory, language, executive function, visuospatial skills, and behavior in patients with dementia 2
Brief screening tools such as MoCA, MMSE, or Mini-Cog can be used for initial cognitive assessment 2
A comprehensive cognitive assessment must cover multiple domains, including memory, language, attention, executive function, and visuospatial function 2, 3
Formal neuropsychological testing may be necessary when office-based assessment is inconclusive or when complex clinical profiles exist 2, 3

Vascular risk factors such as hypertension, diabetes, hyperlipidemia, smoking, and obesity are associated with an increased risk of dementia 4, 3
Cerebrovascular disease history, including stroke, TIA, and cardiovascular disease, is relevant in dementia evaluation 4
Sleep disorders, particularly obstructive sleep apnea, and alcohol and substance use should be assessed in patients with dementia 3
A complete medication review, including over-the-counter preparations, is essential in dementia evaluation 4, 3
A family history of dementia, neurological disorders, or psychiatric conditions in first-degree relatives is relevant in dementia evaluation 4

Laboratory tests in dementia have three main purposes: to rule out potentially reversible causes of cognitive decline, to identify comorbidities that may exacerbate cognitive decline, and to support etiological diagnosis in specific cases 1
Tier 1 laboratory tests, including complete blood count, comprehensive metabolic panel, thyroid function tests, vitamin B12 and folate levels, and glucose level, are recommended in dementia evaluation 3
Tier 2 laboratory tests, such as erythrocyte sedimentation rate or C-reactive protein, syphilis serology, HIV testing, ammonia level, and toxicology screen, may be indicated in certain cases 3
Laboratory screening, including CBC, comprehensive metabolic panel, thyroid function, vitamin B12, and folate levels, is recommended as part of a standard dementia workup 5, 2

Structural brain imaging, preferably MRI or CT scan, is necessary to identify structural abnormalities, vascular changes, and patterns of atrophy in patients with dementia 2, 3
Advanced imaging, such as FDG-PET, amyloid PET, or tau PET, may be indicated in atypical presentations or diagnostic uncertainty 2
Neuroimaging, such as MRI or CT, is essential to exclude other causes of cognitive impairment, and advanced testing, including CSF biomarkers, may be considered in atypical cases to help exclude Alzheimer's disease 2, 6

Biomarkers such as low levels of Aβ42 in cerebrospinal fluid (CSF) and positive amyloid PET can support etiological diagnosis, but are not diagnostic on their own, as stated by the American College of Radiology 1
Biomarkers of neuronal injury, such as elevated tau in CSF and decreased FDG uptake in temporoparietal cortex on PET, can also support etiological diagnosis 1
Blood-based biomarkers (emerging) have sensitivity and specificity of ~90% for amyloid pathology, according to Nature Reviews Neurology 7
CSF biomarkers, including amyloid-β, phosphorylated tau, and total tau, may be useful in diagnosing dementia, particularly in early-onset or rapidly progressive cases 6

The diagnostic approach to dementia should include a combination of clinical evaluation, laboratory tests, and neuroimaging, with biomarkers used to support etiological diagnosis in selected cases, as recommended by the American College of Radiology 1
Determine cognitive functional status, including cognitively unimpaired, subjective cognitive decline, mild cognitive impairment, or dementia 2, 3
Identify the cognitive-behavioral syndrome, including amnestic vs. non-amnestic presentation, single vs. multiple domain impairment, and presence of behavioral/psychiatric symptoms 2, 3
Determine the likely etiology of dementia, including Alzheimer's disease, vascular cognitive impairment, Lewy body dementia, frontotemporal dementia, or mixed etiology 2, 3

Pseudodementia is characterized by a rapid onset, often with a clear temporal relationship to mood symptoms, and may plateau or fluctuate, unlike the gradual progression seen in neurodegenerative dementia 5
The diagnostic feature of pseudodementia includes significant discrepancy between reported impairment and observed function, which can be assessed through standardized mood assessments, such as PHQ-9, GDS, or NPI-Q 8
The following table summarizes the key features that differentiate pseudodementia from true dementia:

Feature	Pseudodementia	True Dementia
Onset	Rapid, often with clear temporal relationship to mood symptoms	Gradual, insidious
Symptom progression	May plateau or fluctuate	Progressive worsening
Complaint pattern	Patient emphasizes disabilities, often with detailed complaints	Patient often minimizes or is unaware of deficits
Response to questions	"Don't know" answers common	Confabulation or approximate answers
Effort on testing	Variable, often improves with encouragement	Consistent effort despite failures
Nocturnal exacerbation	Uncommon	Common
Remote memory	Equally impaired as recent memory	Better preserved than recent memory	[8]

Prompt referral for psychiatric evaluation and treatment is essential when pseudodementia is suspected, and improvement in cognitive function with appropriate treatment of the underlying psychiatric condition supports the diagnosis of pseudodementia 5
Regular follow-up is crucial, as some patients with initial pseudodementia may later develop true dementia, and overlooking comorbidity, premature diagnosis, misinterpreting test results, and ignoring functional assessment can lead to inaccurate diagnosis and inadequate treatment 5, 2