What are the different types of dementia?

Types of Dementia

Dementia encompasses over 100 different neurodegenerative conditions, with the most common types being Alzheimer disease (50-75% of cases), vascular dementia (20%), dementia with Lewy bodies (5%), frontotemporal dementia (5%), and mixed dementia attributed to multiple causes. 1, 2

Major Dementia Types

Most Common Forms

• Alzheimer Disease (AD) represents the predominant form, accounting for 50-75% of all dementia cases and characterized by progressive memory impairment and cognitive decline 1, 2

• Vascular Dementia (VaD) comprises approximately 20% of cases and results from cerebrovascular disease with MRI indicators of infarcts and/or white matter hyperintensities 1, 2

• Dementia with Lewy Bodies (DLB) accounts for roughly 5% of cases and commonly presents with fluctuating cognition, visual hallucinations, and behavioral symptoms 1, 3, 2

• Frontotemporal Dementia (FTD) represents about 5% of cases, with the behavioral variant being a distinct clinical entity 1, 2

• Mixed Dementia involves multiple contributing pathologies occurring simultaneously, which is increasingly recognized in older adults, particularly those over age 80 1

Less Common Forms

• Parkinson's Disease Dementia develops in patients with established Parkinson's disease and shares overlapping features with DLB 1

• Limbic-predominant Age-related TDP-43 Encephalopathy (LATE) is a recently characterized non-AD pathology that mimics AD clinically 1

• Progressive Supranuclear Palsy (PSP) and Corticobasal Degeneration represent rarer parkinsonian syndromes with cognitive impairment 1

• Huntington's Disease causes dementia in the context of autosomal dominant genetic mutation with characteristic motor symptoms 1

• Creutzfeldt-Jakob Disease and other prion diseases cause rapidly progressive dementia 1

• Korsakoff Disease results from thiamine deficiency, typically related to chronic alcohol use 1

• Normal Pressure Hydrocephalus (NPH) presents with the classic triad of gait disturbance, urinary incontinence, and cognitive impairment 1

Clinical Distinctions

Primary Progressive Aphasia (PPA)

• PPA can be an atypical presentation of AD, especially the logopenic variant, or may represent frontotemporal pathology 1

• Three main variants exist: logopenic (often AD), semantic, and nonfluent/agrammatic (typically FTD) 1

Rapidly Progressive Dementias (RPD)

• RPD can result from prion diseases, atypical or rapid onset neurodegenerative diseases, infectious/inflammatory conditions, neoplastic and paraneoplastic conditions, vascular conditions, and toxic/nutritional/metabolic disorders 1

Pathophysiological Considerations

Biomarker Classification for AD

• Core AD biomarkers include amyloid-beta (detected via PET, CSF, or plasma) and phosphorylated tau species (p-tau 217, p-tau 181, p-tau 231) 1

• Non-specific processes involved in AD include neurodegeneration (neurofilament-light, MRI measures, FDG-PET hypometabolism) and astrocytic activation (GFAP) 1

• Non-AD pathology biomarkers include vascular brain injury markers and alpha-synuclein seed amplification assays 1

Mixed Etiology Dementia

• Mixed pathologies are frequently detected in older adults' brains and have important clinical implications 4

• Patients with mixed etiology dementia are more likely to present with atypical or non-amnestic symptoms 1

• Contributing conditions include obstructive sleep apnea, cognitively impairing medications, excessive alcohol consumption, and cerebrovascular disease 1

Important Clinical Pitfalls

• Younger-onset dementia (age <65 years) accounts for up to 8% of cases, with different etiological distributions including traumatic brain injury and brain tumors being more common 1, 5

• Undiagnosed dementia remains highly prevalent globally due to reluctance to discuss symptoms, denial, stigma, fear, and normalization of cognitive changes 1

• Psychiatric disorders can mimic dementia (formerly called pseudodementia), but mood changes are also very common early symptoms of AD or other dementias, making differentiation challenging 1

• Autosomal dominant AD caused by mutations in amyloid precursor protein, presenilin 1, or presenilin 2 genes causes early-onset disease but shares the same pathophysiology as late-onset AD 1