Definition and epidemiology
Dementia (now termed major neurocognitive disorder in DSM-5) is a syndrome of acquired, chronic, and usually progressive decline in one or more cognitive domains (memory, executive function, language, visuospatial skills, or behavior/personality) that is severe enough to interfere with independent functioning in daily life. It occurs in clear consciousness, which separates it from delirium.
- Prevalence rises steeply with age: roughly 5-8% of people over 65, approaching 30-40% by age 85 in most Western epidemiologic surveys.
- Alzheimer disease (AD) accounts for the majority of cases (about 60-70%), followed by vascular dementia and Lewy body dementia.
- Mixed pathology (AD plus vascular changes) is common in autopsy series of elderly patients.
- Early-onset dementia (before age 65) is less common and should prompt a search for genetic, autoimmune, or reversible causes.
- Dementia occurs with clear consciousness; delirium has fluctuating consciousness — key distinguishing feature
- Alzheimer disease is the most common cause of dementia overall
- Always screen for reversible causes: hypothyroidism, B12 deficiency, NPH, subdural hematoma, neurosyphilis
- Vascular dementia classically shows stepwise decline with focal neurologic signs
- Lewy body dementia triad: fluctuating cognition, visual hallucinations, parkinsonism
- Frontotemporal dementia presents with early personality/behavior change, memory relatively spared early
- NPH triad: gait disturbance, urinary incontinence, dementia ("wet, wobbly, wacky")
- Cholinesterase inhibitors are first-line pharmacotherapy for mild-moderate Alzheimer disease; memantine added in moderate-severe disease
Etiology and risk factors
Degenerative
- Alzheimer disease
- Lewy body dementia and Parkinson disease dementia
- Frontotemporal dementia (FTD)
- Huntington disease
Vascular
- Multi-infarct (vascular) dementia
- Chronic small vessel ischemic disease
Reversible or partially reversible causes (always screen for these)
- Hypothyroidism
- Vitamin B12 deficiency
- Normal pressure hydrocephalus (NPH)
- Chronic subdural hematoma
- Neurosyphilis, HIV-associated neurocognitive disorder
- Depression ("pseudodementia")
- Medication effects (anticholinergics, sedatives) and chronic alcohol use
Risk factors
- Advancing age (strongest risk factor)
- Family history, APOE e4 allele (AD), Down syndrome (early AD)
- Cardiovascular risk factors: hypertension, diabetes, smoking, hyperlipidemia (especially for vascular dementia)
- Low educational attainment, head trauma, social isolation
Pathophysiology
- Alzheimer disease: extracellular beta-amyloid plaques and intracellular hyperphosphorylated tau neurofibrillary tangles lead to neuronal loss and cortical atrophy, especially hippocampus and temporoparietal cortex. Cholinergic neuron loss in the basal forebrain underlies the cholinesterase inhibitor rationale.
- Vascular dementia: cumulative ischemic injury from multiple infarcts or chronic small vessel disease causes stepwise cognitive decline, often with focal neurologic signs.
- Lewy body dementia: alpha-synuclein aggregates (Lewy bodies) in cortex and brainstem; overlaps pathologically with Parkinson disease.
- Frontotemporal dementia: focal atrophy of frontal and temporal lobes, associated with tau or TDP-43 inclusions; presents with behavioral/personality change or language decline out of proportion to memory loss.
- NPH: impaired CSF resorption causing ventricular dilation with relatively normal opening pressure, producing the classic gait-cognition-incontinence triad.
Clinical features
Core features
- Progressive memory impairment (especially short-term/recent memory in AD)
- Executive dysfunction, impaired judgment and planning
- Language difficulty (aphasia), apraxia, agnosia
- Behavioral and psychological symptoms: apathy, depression, agitation, psychosis (later stages)
- Progressive loss of independence in instrumental then basic activities of daily living
Distinguishing patterns
| Type | Hallmark features |
|---|---|
| Alzheimer disease | Gradual onset, early memory loss, later language/visuospatial decline |
| Vascular dementia | Stepwise decline, focal deficits, history of stroke/vascular risk factors |
| Lewy body dementia | Fluctuating cognition, visual hallucinations, parkinsonism, REM sleep behavior disorder |
| Frontotemporal dementia | Early personality/behavioral change or language decline, relatively preserved memory early |
| NPH | Gait disturbance, urinary incontinence, cognitive decline (triad) |
Diagnosis
Diagnosis is primarily clinical, based on history (ideally from a reliable informant), cognitive testing, and exclusion of reversible causes.
Cognitive screening tools
- Mini-Mental State Examination (MMSE)
- Montreal Cognitive Assessment (MoCA) — more sensitive for mild/early impairment
Required workup to exclude reversible causes
- CBC, electrolytes, renal and liver function
- TSH, vitamin B12 level
- Neuroimaging (MRI preferred, or CT) to exclude structural lesions, NPH, chronic subdural hematoma, and to assess vascular burden
- Consider HIV, syphilis serology, and depression screening in appropriate clinical contexts
Advanced testing
- Neuropsychological testing for atypical or early-onset presentations
- CSF amyloid/tau or amyloid PET imaging in research or specialized settings
- Genetic testing (e.g., presenilin, APP mutations) in suspected familial early-onset AD
Differential diagnosis
- Delirium: acute onset, fluctuating consciousness, often reversible — the key distinction from dementia
- Mild cognitive impairment (MCI): cognitive decline without significant functional impairment
- Depression (pseudodementia): subjective memory complaints often exceed objective deficits, mood symptoms prominent, may improve with treatment
- Normal age-related cognitive decline: mild, non-progressive, does not impair function
- Substance-induced cognitive disorder: chronic alcohol use (Wernicke-Korsakoff), medication effects
Management
Management is multimodal; no treatment cures the underlying neurodegeneration in most dementia types.
Pharmacologic (Alzheimer disease and some mixed/Lewy body cases)
- Cholinesterase inhibitors (donepezil, rivastigmine, galantamine): first-line for mild to moderate AD and often used in Lewy body/Parkinson disease dementia
- Memantine (NMDA receptor antagonist): used in moderate to severe AD, alone or added to a cholinesterase inhibitor
- Antipsychotics are used cautiously and only for severe agitation/psychosis refractory to non-pharmacologic measures, given an increased risk of stroke and mortality in elderly dementia patients (regulatory warnings from the FDA and EMA)
Non-pharmacologic
- Caregiver education and support, structured routines, environmental safety modification
- Cognitive stimulation activities, physical exercise
- Treatment of reversible contributing factors (correct B12/thyroid, manage vascular risk factors)
- Advance care planning and goals-of-care discussions early in the disease course
Vascular dementia specific
- Aggressive management of vascular risk factors (antihypertensives, statins, antiplatelet therapy, smoking cessation, glycemic control) to slow progression; cholinesterase inhibitors have modest evidence
NPH
- Ventriculoperitoneal shunting can reverse symptoms if diagnosed early
Guideline bodies (WHO, American Academy of Neurology, NICE) consistently emphasize non-pharmacologic support and caregiver involvement as central to care, with pharmacotherapy offering modest symptomatic benefit rather than disease reversal.
Complications and prognosis
- Progressive functional decline leading to total dependence for activities of daily living
- Increased risk of falls, fractures, aspiration pneumonia, and malnutrition
- Behavioral and psychological symptoms (agitation, wandering, psychosis) increase caregiver burden and institutionalization risk
- Median survival after diagnosis varies by type and age at onset, generally ranging from about 3 to 10 years, with aspiration pneumonia a common terminal event
- Lewy body dementia and advanced vascular dementia tend to have a more rapid functional decline than typical Alzheimer disease
NPH triad — "Wet, Wacky, Wobbly": urinary incontinence (wet), cognitive decline (wacky), gait disturbance (wobbly).
Practice questions
1. A 78-year-old woman is brought in by her daughter for progressive memory loss over the past 2 years. She now repeats questions and has gotten lost while driving to familiar places. She is alert and attentive during the interview. Neurologic exam is nonfocal. Which of the following is the most likely diagnosis?
2. A 70-year-old man with a history of hypertension and two prior strokes presents with cognitive decline that his wife describes as occurring in sudden drops followed by plateaus rather than a steady decline. Exam shows mild left-sided weakness and a wide-based gait. Which type of dementia best fits this presentation?
3. A 68-year-old man presents with fluctuating cognition, visual hallucinations of small animals in his home, and a resting tremor with rigidity. His wife also reports he acts out vivid dreams during sleep, sometimes punching at the air. Which medication class should be used cautiously due to increased sensitivity in this condition?
Frequently asked questions
What causes dementia?
Dementia is most often caused by neurodegenerative diseases, primarily Alzheimer disease, followed by cerebrovascular disease (vascular dementia) and Lewy body disease. Other causes include frontotemporal degeneration, chronic alcohol use, and potentially reversible conditions like hypothyroidism, vitamin B12 deficiency, normal pressure hydrocephalus, and chronic subdural hematoma, which is why initial workup always screens for these treatable contributors.
What are the first symptoms of dementia?
The earliest symptoms typically involve subtle short-term memory lapses, such as repeating questions or misplacing items, along with difficulty with complex tasks like managing finances. In frontotemporal dementia, early symptoms are often personality or behavioral changes rather than memory loss. Family members frequently notice these changes before the patient does, since insight is often impaired.
How is dementia diagnosed?
Dementia is diagnosed clinically through a detailed history (often from a caregiver), cognitive screening tools like the MMSE or MoCA, and confirmation that cognitive decline impairs daily functioning. Laboratory tests (TSH, B12) and brain imaging (MRI or CT) are required to rule out reversible causes and structural lesions before attributing symptoms to a primary neurodegenerative process.
Is dementia curable?
Most forms of dementia, including Alzheimer disease, vascular dementia, and Lewy body dementia, are not curable and tend to be progressive. However, dementia-like symptoms from reversible causes such as hypothyroidism, B12 deficiency, or normal pressure hydrocephalus can improve significantly or resolve with appropriate treatment, which is why these causes must always be excluded first.
Dementia vs delirium — what is the difference?
Delirium has an acute onset (hours to days), fluctuates throughout the day, and involves impaired or clouded consciousness and attention, often triggered by an acute illness or medication. Dementia develops gradually over months to years, is generally stable day-to-day, and occurs with clear consciousness. Delirium is often reversible once the underlying cause is treated, while dementia is usually chronic and progressive.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: F06
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.