Dementia (Major Neurocognitive Disorder)

Reference Images

Dementia FDG PET imaging patterns — Dementia FDG-PET PatternsClick to enlarge

Global Cortical Atrophy scale — Global Cortical Atrophy ScaleClick to enlarge

Koedam posterior cortical atrophy score — Koedam Posterior Atrophy ScoreClick to enlarge

Medial Temporal Atrophy score — Medial Temporal Atrophy ScoreClick to enlarge

Overview

Dementia—relabelled major neurocognitive disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5)—is a clinical syndrome defined by progressive decline in one or more cognitive domains relative to a person’s premorbid functional level. To fulfill criteria for dementia, the resulting cognitive impairment must significantly interfere with independence in performing activities of daily living.^1,2

Terminology

The use of dementia in the literature is heterogeneous, with varying definitions.⁸ Some authors include reversible and irreversible causes of cognitive impairment, while others state that dementia is irreversible⁶ and exclude reversible conditions. Thus, chronic subdural hematoma and normal pressure hydrocephalus may or may not be included as causes, depending on the definition.

Given this heterogeneity, it is prudent to use the word increasingly sparingly¹⁰ and reserve it for the conditions broadly accepted as irreversible neurodegenerative disease, such as Alzheimer disease and frontotemporal lobar degeneration.

Young-onset dementia, also called early-onset dementia and historically presenile dementia, generally refers to onset before age 65 (reported definitions range from 60–70 years).⁷ Rapidly progressive dementia describes dementia progressing over weeks to months.

FDG-PET Imaging Patterns

These simplified visual pattern-recognition aids derive from a 2006 teaching document.

1. Alzheimer’s disease (AD)Decreased metabolism in the parietal and temporal regions. The distribution resembles the Nike swoosh.
Memory aid: the Nike swoosh pattern is associated with Alzheimer’s disease.

2. Dementia with Lewy bodies (DLB)Temporoparietal hypometabolism similar to Alzheimer disease, with additional occipital involvement; it may extend farther into the anterior temporal cortex. The distribution resembles the letter L.
Memory aid: Lewy begins with L.

3. Frontotemporal dementia (FTD)Hypometabolism involving the frontal and temporal lobes with additional anterior cingulate involvement. The distribution resembles a lowercase letter f.
Memory aid: frontotemporal dementia begins with f.

4. Posterior cerebral atrophyMay be associated with Alzheimer disease or DLB. Hypometabolism involves the occipital and posterior temporal lobes with relative anterior temporal preservation. The distribution resembles a C rather than the L-shaped DLB pattern.
Memory aid: posterior cerebral atrophy (pCa) — C-shaped pattern.

5. Vascular dementiaVariable distribution based on infarct location. Cortical infarctions may create wedge-shaped hypometabolic regions resembling an inverted V.
Memory aid: V represents both vascular and variable.

Clinical Interpretation

Do not use in isolation

FDG-PET findings should be interpreted alongside clinical history, cognitive phenotype, structural imaging, laboratory evaluation, and other diagnostic information rather than used as standalone diagnostic criteria.

Pattern overlap

AD and DLB may both show temporoparietal hypometabolism.
Occipital involvement favors DLB in the appropriate context.
Posterior cerebral atrophy may reflect AD or DLB pathology.
Vascular patterns vary with infarct location and burden.

Etiology — Neurodegenerative

Alzheimer disease
- Posterior cortical atrophy
Vascular dementia
- Cerebral small vessel diseases
Limbic-predominant age-related TDP-43 encephalopathy (LATE)
Primary age-related tauopathy (PART)
Argyrophilic grain disease (AGD)
Lewy body dementia
- Dementia with Lewy bodies
- Parkinson disease dementia

Frontotemporal lobar degeneration
- Behavioral variant FTD
- Primary progressive aphasia
- Right temporal variant FTD
- Corticobasal degeneration
- Progressive supranuclear palsy
Multiple system atrophy
Cerebral amyloid angiopathy
Chronic traumatic encephalopathy
Huntington disease
Fahr disease
Prion disease, including Creutzfeldt-Jakob disease
Leukodystrophies

Other CNS Pathology

These causes are not strictly neurodegenerative and may be reversible:

Chronic subdural hematoma
Normal pressure hydrocephalus
Brain tumor
Spontaneous intracranial hypotension (frontotemporal brain sagging syndrome)
Wilson disease

Psychoactive substances

Alcohol
Sedatives, hypnotics, or anxiolytics
Other substances, including volatile inhalants

Autoimmune and Infection

Autoimmune disorders

Multiple sclerosis
Autoimmune encephalitis
Cerebral vasculitis
Inflammatory cerebral amyloid angiopathy
Systemic lupus erythematosus
Neurosarcoidosis

Infection

HIV-associated dementia
Neurosyphilis
Progressive multifocal leukoencephalopathy
Subacute sclerosing panencephalitis
Whipple disease