Residency · Residency · Psychiatry
Neurocognitive Disorders: Differential Diagnosis and Workup
Introduction
Neurocognitive disorders (NCDs) encompass a spectrum from mild neurocognitive disorder (formerly mild cognitive impairment) to major neurocognitive disorder (dementia). DSM-5 classifies these by etiology, including Alzheimer's disease, vascular disease, Lewy body disease, frontotemporal degeneration, and others. A systematic workup is essential to identify reversible causes, establish an etiological diagnosis, and guide management.
DSM-5 Framework
Mild Neurocognitive Disorder
Modest cognitive decline from a previous level of performance in one or more cognitive domains. Does not interfere with independence in everyday activities. Cognitive concerns reported by the individual, an informant, or clinician, supported by objective testing.
Major Neurocognitive Disorder
Significant cognitive decline in one or more cognitive domains. Interferes with independence in everyday activities. Specify severity: mild, moderate, severe. Specify etiology and presence or absence of behavioral disturbance.
Cognitive Domains
Complex attention. Executive function. Learning and memory. Language. Perceptual-motor function. Social cognition.
Etiological Subtypes
| Subtype | Prevalence | Age of Onset | Early/Cardinal Features | Key Neuroimaging | Distinguishing Feature |
|---|---|---|---|---|---|
| Alzheimer's disease | 60-80% | >65 (typically) | Episodic memory loss | Hippocampal atrophy; amyloid/tau PET+ | Gradual onset; memory predominant |
| Vascular NCD | 15-20% | Variable | Executive dysfunction, processing speed | WMH, lacunar infarcts, strategic infarcts | Stepwise decline; CVD history |
| Lewy body disease | 5-15% | >60 | Fluctuating cognition, visual hallucinations, parkinsonism | May be normal; DaTscan positive | Neuroleptic sensitivity; RBD |
| Frontotemporal | 5-10% | 45-65 | Personality change, disinhibition OR language deficits | Frontal/temporal atrophy | Younger onset; memory preserved early |
| Parkinson's disease dementia | 3-5% | >65 | Subcortical pattern; >1 yr after motor onset | Cortical atrophy; DaTscan+ | Motor symptoms precede dementia |
Alzheimer's Disease
Most common cause of dementia (60-80%) Insidious onset with progressive memory impairment as the hallmark. Early deficits in episodic memory (hippocampal involvement) Language, visuospatial, and executive deficits emerge later. Biomarkers: amyloid-beta reduction and tau elevation in CSF; amyloid and tau PET positivity.
Vascular Neurocognitive Disorder
Second most common cause; often coexists with Alzheimer's disease (mixed dementia) Stepwise decline or temporal association with cerebrovascular events. Prominent executive dysfunction and processing speed impairment. MRI shows white matter hyperintensities, lacunar infarcts, or strategic infarcts.
Lewy Body Disease
Fluctuating cognition, recurrent visual hallucinations, and parkinsonism. REM sleep behavior disorder often precedes cognitive decline. Severe neuroleptic sensitivity (contraindication to typical antipsychotics) DaTscan (dopamine transporter imaging) is a supportive diagnostic tool.
Frontotemporal Degeneration
Younger onset (typically age 45-65) Behavioral variant: personality change, disinhibition, apathy, loss of empathy, compulsive behaviors. Language variants: progressive nonfluent aphasia and semantic dementia. Memory is relatively preserved early in the course.
Other Etiologies
Parkinson's disease dementia: dementia developing at least 1 year after established motor parkinsonism. Traumatic brain injury: history of significant head trauma. HIV-associated NCD: subcortical pattern with psychomotor slowing. Prion disease (CJD): rapid progression, myoclonus, characteristic MRI and EEG findings. Normal pressure hydrocephalus: triad of gait disturbance, urinary incontinence, dementia (potentially reversible) Substance/medication-induced: alcohol, anticholinergics, sedatives.
Diagnostic Workup
Clinical Assessment
Detailed history from patient and reliable informant (essential) Assess functional status: ADLs and IADLs. Neurological examination: gait, motor signs, reflexes, cranial nerves. Cognitive screening: MoCA (more sensitive than MMSE for mild impairment)
Laboratory Studies (Recommended Baseline)
Complete blood count. Comprehensive metabolic panel (including calcium, glucose, renal and hepatic function) Thyroid-stimulating hormone (TSH) Vitamin B12 and folate. Consider: RPR/VDRL, HIV, ESR, urinalysis. Consider ceruloplasmin (if age < 50), heavy metals, or autoimmune panels based on clinical suspicion.
Neuroimaging
MRI brain without contrast is preferred: evaluates atrophy patterns, vascular changes, masses, hydrocephalus. CT head is acceptable if MRI is contraindicated. Functional imaging (FDG-PET, amyloid PET, tau PET, DaTscan) may be indicated when the clinical picture is ambiguous.
Neuropsychological Testing
Formal testing clarifies the pattern and severity of cognitive deficits. Helps distinguish between NCD subtypes and between NCD and psychiatric conditions. Establishes baseline for longitudinal monitoring.
Lumbar Puncture
Indicated when infection, inflammation, or prion disease is suspected. Alzheimer's biomarkers: low amyloid-beta-42, elevated total tau and phospho-tau.
Reversible Causes to Exclude
A commonly used mnemonic is DEMENTIA: Drugs (anticholinergics, benzodiazepines, opioids) Emotional (depression/pseudodementia) Metabolic (thyroid, B12, hepatic or renal failure, electrolytes) Eyes and ears (sensory deficits mimicking cognitive decline) Normal pressure hydrocephalus. Tumors and trauma. Infections (HIV, syphilis, Whipple's, prion) Alcohol and autoimmune.
Key Clinical Pearls
Collateral history from a reliable informant is indispensable; patients with early dementia often lack insight. Rapidly progressive dementia (weeks to months) is a medical emergency: consider CJD, autoimmune encephalitis, malignancy, or infection. Always screen for depression and delirium before diagnosing a neurocognitive disorder. The MoCA is superior to the MMSE for detecting mild cognitive impairment and frontal/executive deficits. Mixed pathology (e.g., Alzheimer's plus vascular disease) is the rule, not the exception, in elderly patients.
References
- McKhann GM, Knopman DS, Chertkow H, et al. The diagnosis of dementia due to Alzheimer's disease: recommendations from the National Institute on Aging-Alzheimer's Association workgroups. Alzheimers Dement. 2011;7(3):263-269.
- McKeith IG, Boeve BF, Dickson DW, et al. Diagnosis and management of dementia with Lewy bodies: fourth consensus report. Neurology. 2017;89(1):88-100.
- Rascovsky K, Hodges JR, Knopman D, et al. Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia. Brain. 2011;134(Pt 9):2456-2477.
- Petersen RC. Mild cognitive impairment as a diagnostic entity. J Intern Med. 2004;256(3):183-194.