Neurocognitive disorders (NCDs) are acquired syndromes of cognitive decline, anchored in DSM-5-TR as a chapter distinct from neurodevelopmental disorders to emphasize loss from a previously attained baseline. The chapter groups three core syndromes — delirium, mild NCD, and major NCD — and then layers etiologic subtypes onto the major and mild categories (Alzheimer disease, vascular, Lewy body, frontotemporal, traumatic brain injury, Parkinson disease, HIV, prion, substance/medication, Huntington disease, and other or multiple etiologies). The clinical bottom line for the general psychiatrist is that the diagnostic task has two layers: first identify the syndrome (delirium versus mild versus major NCD), then identify the etiology, because management diverges sharply by cause. Mild NCD captures the prodromal window in which disease-modifying and risk-reduction strategies are most relevant, while major NCD (formerly Dementia) defines the threshold at which independence is lost. ICD-11 retains the term dementia and reorganizes the cognitive syndromes under chapter 06, but the operational logic mirrors DSM-5-TR. Across subtypes, treatment remains predominantly symptomatic, supportive, and harm-reduction focused, with anti-amyloid antibodies recently introducing the first disease-modifying option for early Alzheimer disease in selected patients.

Neurocognitive disorders are common, age-dependent, and a leading driver of disability and caregiving burden worldwide. Prevalence varies sharply by syndrome and by etiologic subtype, but Alzheimer disease dominates the late-life landscape and vascular contributions are nearly always co-present at autopsy.

Burden and prevalence

• Global dementia prevalence is estimated at roughly 55 million people, with projections to exceed 130 million by 2050 driven by population aging.^[8]
• US prevalence of Alzheimer disease in adults 65 and older is approximately 10–11%, rising steeply with each decade after 65.^[2]
• Mild cognitive impairment (mild NCD) prevalence in adults over 65 is approximately 15–20%, with annual conversion to dementia of about 10–15%.^[3]
• Delirium prevalence is 15–25% on general medical wards, 50% or higher post-hip-fracture and in ICU populations, and up to 80% in mechanically ventilated patients.^[4]

Distribution by etiologic subtype (clinical and autopsy series):

• Alzheimer disease accounts for 60–80% of dementia cases, though pure AD pathology without comorbid vascular or Lewy body disease is uncommon at autopsy.^[2]
• Vascular NCD accounts for roughly 10–20% of dementias as the primary cause, and contributes pathologically to a much larger share.^[5]
• Dementia with Lewy bodies and Parkinson disease dementia together represent the second or third most common neurodegenerative dementia, estimated at 5–10%.^[6]
• Frontotemporal NCD is the most common dementia under age 65, accounting for 10–20% of early-onset cases.^[7]

Sex and demographic patterns

• Women carry a higher absolute prevalence of Alzheimer disease, largely explained by longer life expectancy, though sex-specific biological contributions remain debated.^[2]
• Lower educational attainment, hearing loss, hypertension, obesity, smoking, depression, physical inactivity, diabetes, excess alcohol, traumatic brain injury, air pollution, and social isolation are the 12 modifiable risk factors identified by the Lancet Commission, collectively associated with about 40% of dementia risk.^[8]
• Black and Hispanic populations in the US show 1.5–2-fold higher age-adjusted dementia prevalence, attributed to a mix of vascular risk burden, socioeconomic determinants, and likely under-ascertainment in research cohorts.^[2]

Comorbidity

• Depression occurs in 20–40% of patients with major NCD and is both a risk factor and a prodrome; late-life depression carries roughly double the dementia risk.^[20]
• Psychotic symptoms emerge in 30–50% of patients with Alzheimer disease over the disease course and are nearly defining in dementia with Lewy bodies.^[6]
• Suicide risk is modestly elevated around the time of dementia diagnosis, particularly in younger patients with preserved insight.^[22]

Neurocognitive disorders are heterogeneous at the molecular level, but a small number of proteinopathies and vascular mechanisms explain most cases, often in combination. Understanding the dominant pathology guides both prognosis and a small but growing set of disease-specific therapies.

Alzheimer disease

• Defined neuropathologically by extracellular amyloid-β plaques and intraneuronal neurofibrillary tangles of hyperphosphorylated tau, with synaptic loss and cortical atrophy that begins in medial temporal structures.^[11]
• The amyloid cascade hypothesis posits that Aβ accumulation triggers downstream tau pathology, neuroinflammation, and neurodegeneration, though the temporal and causal links remain incompletely characterized.^[11]
• Heritability is high in early-onset autosomal dominant cases (mutations in APP, PSEN1, PSEN2), while late-onset sporadic AD is strongly influenced by the APOE ε4 allele, which raises risk roughly 3-fold per allele.^[2,11]

Vascular neurocognitive disorder

• Caused by ischemic, hemorrhagic, and small-vessel injury; cortical strokes produce stepwise deficits, while subcortical small-vessel disease produces a more insidious dysexecutive picture.^[5]
• Risk-factor profile mirrors stroke: hypertension, diabetes, hyperlipidemia, atrial fibrillation, smoking, and obstructive sleep apnea.^[5]

Dementia with Lewy bodies and Parkinson disease dementia:

• Both are α-synucleinopathies defined by Lewy body inclusions; the operational distinction is timing — cognitive decline preceding or within one year of parkinsonism defines DLB, while dementia emerging well after established Parkinson disease defines PDD.^[6]
• Cholinergic deficit is profound, often exceeding that of Alzheimer disease, which underlies the marked benefit of cholinesterase inhibitors and the dramatic sensitivity to antipsychotics in this group.^[6]

Frontotemporal lobar degeneration

• A clinicopathologic family with three molecular subtypes (tau, TDP-43, FUS) and three clinical phenotypes: behavioral variant FTD, semantic variant primary progressive aphasia, and nonfluent/agrammatic variant PPA.^[7]
• Up to 40% of cases are familial, with MAPT, GRN, and C9orf72 expansions accounting for most identified mutations; C9orf72 also causes amyotrophic lateral sclerosis, explaining the FTD-ALS overlap.^[7]

Other etiologies

• Traumatic brain injury produces NCD acutely and is associated with chronic traumatic encephalopathy after repetitive head impacts.^[33]
• HIV-associated neurocognitive disorder persists in the antiretroviral era as a milder, predominantly subcortical syndrome.^[13]
• Prion disease (Creutzfeldt-Jakob and variants) produces rapidly progressive dementia with myoclonus over weeks to months.^[15]
• Substance/medication-induced NCD includes alcohol-related (Wernicke-Korsakoff), inhalant, and chronic anticholinergic exposure.^[1]

Delirium pathophysiology

• Final common pathway involves cholinergic deficiency, dopaminergic excess, and neuroinflammation precipitated by systemic illness, surgery, hypoxia, metabolic derangement, infection, or psychoactive medication.^[4]
• Pre-existing cognitive impairment is the single strongest predisposing factor, which is why delirium and dementia so frequently co-occur.^[4]

DSM-5-TR organizes the chapter around three core syndromes — delirium, mild NCD, and major NCD — and then assigns an etiologic subtype to mild and major NCD. The diagnostic moves are sequential: confirm the syndrome, then specify the etiology, then attach severity and behavioral specifiers.

Delirium

• A disturbance in attention and awareness that develops acutely (hours to days), fluctuates over the course of a day, and is accompanied by an additional cognitive disturbance such as memory, language, or perceptual impairment.^[1]
• The disturbance is not better explained by another NCD and does not occur in the context of a severely reduced level of arousal such as coma.^[1]
• Evidence from history, examination, or laboratory findings must support a direct physiological consequence of a medical condition, substance intoxication or withdrawal, medication, toxin exposure, or multiple etiologies.^[1]
• Specifiers cover psychomotor subtype (hyperactive, hypoactive, mixed), duration (acute, persistent), and etiology.^[1]

Major neurocognitive disorder

• Significant cognitive decline from a previous level of performance in one or more cognitive domains (complex attention, executive function, learning and memory, language, perceptual-motor, social cognition), based on concern by the patient or informant and substantiated by standardized testing or equivalent clinical assessment.^[1]
• Cognitive deficits interfere with independence in everyday activities, requiring assistance with instrumental activities of daily living at minimum.^[1]
• Deficits do not occur exclusively in the context of delirium and are not better explained by another mental disorder.^[1]
• Severity is graded as mild (difficulty with instrumental ADLs), moderate (difficulty with basic ADLs), or severe (fully dependent), and a "with behavioral disturbance" specifier flags significant psychotic, mood, agitation, apathy, or other behavioral symptoms.^[1]

Mild neurocognitive disorder

• Modest cognitive decline from a previous level of performance in one or more cognitive domains, based on concern and on documented impairment (typically 1–2 standard deviations below norms on standardized testing).^[1]
• Cognitive deficits do not interfere with independence in everyday activities, though greater effort, compensatory strategies, or accommodation may be required.^[1]
• Deficits do not occur exclusively during delirium and are not better explained by another mental disorder.^[1]

Etiologic subtypes (applied to either mild or major NCD):

• Each subtype carries its own probable / possible criteria. "Probable" generally requires either genetic evidence (family history with a causative mutation or detected mutation) or unequivocal clinical evidence (e.g., a biomarker-supported AD phenotype, neuroimaging documenting cerebrovascular disease tightly linked to onset).^[1]
• The DSM-5-TR subtypes are: Alzheimer disease, vascular, frontotemporal, Lewy body, traumatic brain injury, substance/medication-induced, HIV infection, prion disease, Parkinson disease, Huntington disease, another medical condition, multiple etiologies, and unspecified.^[1]

The clinical picture varies by etiology and stage, but a few cross-cutting patterns recur: an insidious memory-led decline favors Alzheimer disease, stepwise or executive-led decline favors vascular disease, early visual hallucinations and parkinsonism favor Lewy body disease, and early personality or language change favors frontotemporal disease.

Alzheimer disease — typical course

• Insidious onset, gradual progression, with early prominent episodic memory loss (recent events, repeated questions, misplaced items).^[2,11]
• Anomia, visuospatial difficulty (getting lost in familiar places), and impaired complex task performance follow as cortical involvement spreads.^[2]
• Late stages bring loss of basic ADLs, mutism, dysphagia, gait disturbance, and ultimately bed-bound dependence; median survival from diagnosis is roughly 4–8 years but varies widely with age and comorbidity.^[2]
• Atypical presentations include posterior cortical atrophy (visuospatial-led), logopenic primary progressive aphasia, and a dysexecutive/frontal variant.^[11]

Vascular NCD

• Classic stepwise decline temporally linked to clinical strokes, often with focal neurologic findings and prominent executive dysfunction or psychomotor slowing rather than amnesia.^[5]
• Subcortical ischemic vascular dementia from small-vessel disease produces a more insidious dysexecutive, gait-disturbance, urinary urgency picture mimicking neurodegenerative disease.^[5]

Dementia with Lewy bodies

• Core features are fluctuating cognition with pronounced variations in attention and alertness, recurrent visual hallucinations that are typically well-formed and detailed, REM sleep behavior disorder, and one or more spontaneous parkinsonian features.^[6]
• Supportive features include severe neuroleptic sensitivity, autonomic dysfunction (orthostasis, constipation), repeated falls, and systematized delusions.^[6]
• A probable diagnosis requires two core features, or one core feature plus an indicative biomarker (low dopamine transporter uptake on SPECT/PET, MIBG cardiac scintigraphy abnormality, or polysomnographic confirmation of REM sleep behavior disorder).^[6]

Frontotemporal NCD

• Behavioral variant presents with early personality change, disinhibition, apathy, loss of empathy, perseverative or compulsive behavior, hyperorality and dietary changes, and a striking dysexecutive cognitive profile with relatively preserved memory and visuospatial function early on.^[7]
• Semantic variant PPA shows loss of word meaning and object knowledge with fluent but empty speech; nonfluent/agrammatic variant shows effortful, agrammatic speech with apraxia of speech.^[7]
• Onset is typically in the 50s–60s, earlier than typical AD, and approximately 10–15% of bvFTD cases develop concurrent motor neuron disease.^[7]

Delirium — phenotypes

• Hyperactive delirium presents with agitation, hypervigilance, hallucinations, and is most easily recognized but accounts for a minority of cases.^[4]
• Hypoactive delirium presents with lethargy, decreased responsiveness, and psychomotor slowing; it is the most common subtype, the most frequently missed, and carries higher mortality.^[4]
• Mixed delirium shows fluctuation between hyper- and hypoactive states within hours.^[4]

The differential begins with a syndromic question (is this delirium, depression, or a chronic NCD?) and then proceeds to subtype. Reversible mimics must be excluded before a degenerative label is committed to the chart.

Across-NCD comparison

Delirium versus dementia versus depression

• Delirium is acute, fluctuates within the day, and prominently impairs attention; dementia is chronic and progressive with attention relatively preserved until late; depression (pseudodementia) shows prominent "don't know" answers, mood-congruent complaints, and effort-dependent performance.^[4,20]
• A new cognitive change in a hospitalized older adult is delirium until otherwise excluded.^[4]
• Depression and dementia coexist often; an empiric antidepressant trial is reasonable when the clinical picture is mixed.^[20]

Reversible and partially-reversible mimics to exclude

• Hypothyroidism, vitamin B12 deficiency, neurosyphilis, HIV, hypercalcemia, hepatic and renal encephalopathy, chronic anticholinergic burden.^[2,21]
• Normal-pressure hydrocephalus (gait disturbance, urinary incontinence, cognitive impairment) — gait usually dominant and CSF tap test guides shunt candidacy.^[21]
• Obstructive sleep apnea, severe untreated depression, and polypharmacy can mimic or magnify dementia.^[8,21]
• Subdural hematoma, particularly in older adults on anticoagulants, can present as a subacute cognitive decline.^[21]
• Autoimmune encephalitis (e.g., anti-NMDA receptor, LGI1) presents subacutely with cognitive, psychiatric, and seizure features and is treatable.^[12,21]

Assessment serves three purposes: confirm the cognitive impairment objectively, characterize its domain pattern, and exclude reversible causes. The order is interview, examination, cognitive testing, then targeted laboratory and imaging studies.

History and informant interview

• Onset, tempo, and domain-by-domain trajectory of change, with attention to functional decline in instrumental ADLs (finances, medications, driving, meal preparation) and basic ADLs.^[2]
• Always obtain collateral history; the patient's own report systematically underestimates deficit in major NCD and overestimates it in depression.^[2,20]
• Medication review with attention to anticholinergics, benzodiazepines, opioids, sedating antihistamines, and antiepileptics; the Beers and STOPP criteria are clinically useful frames.^[23]
• Sleep history (REM sleep behavior disorder is a Lewy body red flag), gait and fall history, behavioral and psychiatric symptoms, suicidal ideation, and driving safety.^[6,10]

Examination

• General and neurologic examination, including gait, tone, tremor, ocular movements (slow vertical saccades raise progressive supranuclear palsy), and frontal release signs.^[21]
• Cardiovascular exam for atrial fibrillation, carotid bruits, and orthostatic vital signs.^[5]
• Sensory examination including hearing and vision, both of which are independently linked to cognitive performance and dementia risk.^[8]

Cognitive screening and neuropsychological testing

• The Mini-Mental State Examination (MMSE, /30) is widely used but insensitive to mild NCD and to frontal/subcortical dysfunction; the Montreal Cognitive Assessment (MoCA, /30) is preferred for mild impairment screening with a typical cutoff of 26.^[17]
• Mini-Cog (three-item recall plus clock draw) is a fast primary-care screen.^[3]
• Formal neuropsychological testing is indicated when the diagnosis is uncertain, the patient is high-functioning, the deficits are atypical, or there is medicolegal need (capacity, driving).^[3]

The MoCA outperforms the MMSE for detecting mild neurocognitive disorder.^[17] Laboratory workup (recommended in all new dementia evaluations):

• CBC, basic metabolic panel, calcium, liver enzymes, TSH, vitamin B12, and HIV testing where risk factors are present.^[2,21]
• Syphilis serology, urinalysis, and folate are obtained selectively based on history.^[21]
• Apolipoprotein E genotyping is generally not recommended for diagnosis; it is required when prescribing anti-amyloid antibodies to risk-stratify amyloid-related imaging abnormalities (ARIA).^[19]

Neuroimaging

• Structural MRI (or noncontrast CT if MRI is contraindicated) is recommended at least once in every new dementia evaluation to assess for atrophy patterns, cerebrovascular disease, hydrocephalus, neoplasm, and subdural collections.^[2,21]
• FDG-PET helps differentiate AD (temporoparietal hypometabolism) from frontotemporal disease (frontal/anterior temporal hypometabolism) when clinical and MRI features are equivocal.^[7,11]
• Amyloid PET, tau PET, and CSF biomarkers (Aβ42, total tau, phospho-tau) are increasingly used to confirm Alzheimer pathology, particularly when disease-modifying therapy is being considered.^[18-19]
• Dopamine transporter (DAT) SPECT is the imaging biomarker of choice for Lewy body disease when clinical features are insufficient.^[6]

What not to order

• Routine EEG, lumbar puncture, and paraneoplastic panels are not part of a baseline workup and should be reserved for rapidly progressive, atypical, or autoimmune-suspect presentations.^[12,21]
• Genetic testing for autosomal dominant AD or familial FTD is reserved for early-onset cases with a clear family history, with genetic counseling.^[7,11]

Management is etiology-specific and shifts emphasis with stage: in mild NCD the goal is risk-factor modification and surveillance; in major NCD the goals are symptomatic benefit, behavioral safety, caregiver support, and advance care planning. Anti-amyloid antibodies have introduced the first disease-modifying option for biomarker-confirmed early Alzheimer disease, with substantial caveats.

Pharmacotherapy

• Cholinesterase inhibitors are recommended for mild-to-moderate Alzheimer disease and for dementia with Lewy bodies and Parkinson disease dementia, with modest but consistent symptomatic benefit on cognitive and functional outcomes.^[2,6,18]
  • donepezil 5–10 mg PO QHS is approved for mild, moderate, and severe AD.^[18]
  • rivastigmine 1.5–6 mg PO BID or 4.6–13.3 mg/24 h transdermal patch, approved for AD and PD dementia.^[18]
  • galantamine 8–12 mg PO BID immediate-release or 16–24 mg extended-release daily for AD.^[18]
• Memantine, an uncompetitive NMDA antagonist, is recommended for moderate-to-severe AD as monotherapy or combined with a cholinesterase inhibitor.^[18]
  • memantine 10 mg PO BID after titration; renally dose-adjust.^[18]
• Anti-amyloid monoclonal antibodies (lecanemab, donanemab) are FDA-approved for early Alzheimer disease (mild NCD or mild dementia due to AD) with biomarker-confirmed amyloid pathology, conferring modest slowing of cognitive decline over 18 months at the cost of ARIA risk and IV infusion logistics.^[19,34-35]
  • Patients must have biomarker-confirmed amyloid (CSF or PET), be in early stages, and undergo APOE genotyping with structured MRI surveillance for ARIA-E (edema) and ARIA-H (hemorrhage).^[19]
• Vascular NCD has no specific approved cognitive-enhancing therapy; aggressive control of vascular risk factors (blood pressure, glucose, lipids, atrial fibrillation, smoking) is the standard of care, with limited evidence for cholinesterase inhibitors in mixed AD-vascular disease.^[5]
• Frontotemporal NCD has no approved disease-modifying or cognitive-enhancing therapy; cholinesterase inhibitors are not effective and may worsen behavioral symptoms, so they are avoided.^[7]
• Behavioral and psychological symptoms of dementia (BPSD) are managed first with nonpharmacologic measures; when pharmacotherapy is necessary, evidence supports cautious short courses of atypical antipsychotics with explicit harm-benefit discussion.^[25]
  • Brexpiprazole is FDA-approved for agitation associated with Alzheimer disease at 2–3 mg PO daily, with modest effect sizes and the class boxed warning.^[26]
  • SSRIs (e.g., citalopram 10–20 mg PO QD, sertraline) have evidence for agitation and depression in dementia; citalopram is dose-limited to 20 mg in older adults due to QTc prolongation.^[27]
  • Pimavanserin is approved for Parkinson disease psychosis and may be considered for DLB psychosis, though efficacy and safety in dementia-related psychosis broadly remain debated.^[6]

Psychotherapy and psychosocial interventions

• Caregiver education, structured psychoeducation, and skills training reduce caregiver burden and may delay institutionalization.^[24,28]
• Cognitive stimulation therapy has moderate-quality evidence for improving cognition and quality of life in mild-to-moderate dementia.^[28]
• Reminiscence therapy, music-based interventions, and tailored activity programs reduce agitation in major NCD.^[28]
• CBT and behavioral activation are appropriate for comorbid depression and anxiety in mild NCD and early major NCD.^[20]

Neuromodulation

• ECT can be considered for severe depression with NCD, particularly when psychotic, catatonic, or treatment-resistant; cognitive side effects warrant careful monitoring but ECT is not contraindicated by dementia.^[29]
• Transcranial magnetic stimulation, transcranial direct current stimulation, and deep-brain stimulation for dementia are investigational; current evidence does not support routine clinical use.^[29]

Adjunctive

• The 12 modifiable risk factors identified by the Lancet Commission frame multidomain risk reduction in mild NCD: hypertension control, hearing aids, physical activity, smoking cessation, alcohol moderation, diabetes control, healthy diet, social engagement, treatment of depression, traumatic brain injury prevention, reduction of air pollution exposure, and educational/cognitive engagement.^[8]
• Multidomain lifestyle interventions (e.g., the FINGER trial design — diet, exercise, cognitive training, vascular risk monitoring) showed modest cognitive benefit in at-risk older adults over two years.^[30]
• Sleep optimization, hearing-aid fitting, and de-prescribing of anticholinergic and sedative-hypnotic drugs are high-yield, low-risk interventions across all NCD subtypes.^[8,23]
• Advance care planning, driving evaluation, financial capacity assessment, and caregiver respite planning should be initiated at diagnosis and revisited annually.^[2]

Delirium-specific management

• The cornerstone is identification and reversal of precipitants: infection, hypoxia, metabolic derangement, urinary retention, fecal impaction, pain, and offending medications.^[4]
• Nonpharmacologic prevention bundles (the HELP and ABCDEF bundles) reduce delirium incidence and duration on medical and ICU wards.^[4]
• Antipsychotics do not shorten delirium duration in most trials and are reserved for severe agitation threatening safety or essential care.^[4]
• Benzodiazepines should be avoided except in alcohol or sedative-hypnotic withdrawal delirium, where they are first-line.^[4]

The harms picture in NCD is dominated by the medications used to manage behavioral symptoms rather than by cognition-enhancing drugs, and by the limitations of an evidence base built largely in selected, English-speaking, predominantly white research populations. Diagnostic uncertainty itself is a harm: mislabeling delirium as dementia leads to under-treatment of reversible causes, and mislabeling depression-related cognitive impairment as major NCD leads to therapeutic nihilism.

Common adverse effects

• Cholinesterase inhibitors cause nausea, vomiting, diarrhea, anorexia, bradycardia, and vivid dreams; the transdermal patch reduces GI burden compared with oral formulations ^[18].
• Memantine is generally well tolerated; dizziness, headache, and constipation are most common ^[18].
• Atypical antipsychotics cause sedation, weight gain, metabolic disturbance, extrapyramidal symptoms, and orthostatic hypotension ^[25].
• SSRIs in older adults carry risk of hyponatremia, GI bleeding (especially with NSAIDs or anticoagulants), and falls ^[27].

Serious or rare adverse effects

• Antipsychotic use in dementia is associated with a 1.6–1.7-fold increase in mortality, predominantly cardiovascular and infectious, leading to the class-wide FDA boxed warning ^[25].
• Severe neuroleptic sensitivity in DLB can produce irreversible parkinsonism and an NMS-like syndrome ^[6].
• ARIA-E and ARIA-H complicate anti-amyloid therapy, with higher rates and severity in APOE ε4 homozygotes; symptomatic ARIA and fatalities have been reported ^[19].
• Cholinesterase inhibitors can precipitate syncope, complete heart block, and falls in patients with conduction disease ^[18].

Monitoring, withdrawal, and discontinuation

• Cholinesterase inhibitor and memantine discontinuation can produce acute cognitive and behavioral decline; tapering with close monitoring is recommended when stopping ^[18].
• Anti-amyloid therapy requires structured MRI surveillance at fixed timepoints and adjustment or pause for moderate or severe ARIA ^[19].
• Benzodiazepine and Z-drug use in NCD worsens cognition, increases falls, and may contribute to chronic cognitive decline; de-prescribing is a high-yield intervention ^[23].

Limitations of the evidence base

• Most pharmacotherapy trials are 6–18 months long; long-term benefits and disease-modifying claims must be interpreted cautiously ^[18-19].
• Trial populations underrepresent older-old patients (>85), people with significant medical comorbidity, non-white populations, and those with mixed pathology — the dominant clinical reality ^[8,18].
• Behavioral symptom trials use heterogeneous outcome measures, complicating cross-trial comparisons ^[25].
• Biomarker-based AD diagnosis is reshaping the field, and older trial populations defined clinically may differ from current biomarker-defined cohorts ^[3,19].

Special populations shift both the differential diagnosis and the treatment toolkit. The general principle is to weight reversible causes higher in younger and atypical presentations, and to weight comorbid medical illness and polypharmacy higher in the oldest-old.

Pediatric and adolescent

• Acquired cognitive decline in children most often reflects traumatic brain injury, CNS infection, metabolic and inherited neurologic disease, or treatment effects (chemotherapy, radiation); DSM-5-TR NCDs can apply when the loss is from a previously attained baseline rather than developmental ^[1].
• Distinguishing acquired NCD from intellectual disability and from autism spectrum disorder is critical, since the latter are neurodevelopmental and have not represented a loss from baseline ^[1].

Older adults and the oldest-old

• Mixed pathology is the rule rather than the exception above age 85; pure AD becomes proportionally less common while vascular and Lewy body co-pathology become more common ^[5,8].
• Anticholinergic burden, benzodiazepines, opioids, and Z-drugs are over-represented causes of cognitive decline and delirium; structured de-prescribing using the Beers and STOPP/START criteria is high-yield ^[23].
• Sensory impairment (hearing, vision) magnifies cognitive complaints and is independently associated with dementia risk; hearing aid use is recommended where indicated ^[8].

Perinatal

• Cognitive complaints in pregnancy and postpartum are most often attributable to sleep deprivation, postpartum depression and anxiety, or thyroiditis rather than to a primary NCD ^[1,20].
• New persistent cognitive impairment in a perinatal patient warrants the standard reversible-cause workup, with attention to autoimmune encephalitis, posterior reversible encephalopathy syndrome, and rare CNS thrombotic events ^[12,21].

Comorbid medical illness

• Heart failure, chronic kidney disease, COPD, and diabetes are all independently associated with cognitive decline, partly through vascular and hypoxic mechanisms and partly through medication burden ^[5].
• Cancer survivors may experience treatment-related cognitive impairment (so-called "chemo brain"), which is typically mild, may improve, and should not be reflexively labeled major NCD ^[1].
• Long-COVID cognitive symptoms typically present as subjective complaints with mild or no objective deficit and tend to improve over months; persistent objective deficit warrants standard NCD workup ^[4].

Comorbid substance use

• Alcohol-related cognitive impairment is one of the more reversible major NCDs with sustained abstinence and thiamine repletion ^[21].
• Methamphetamine, inhalants, and chronic high-dose benzodiazepines all produce cognitive impairment that may improve substantially with abstinence ^[21].
• Cannabis is associated with subtle cognitive changes that largely resolve after extended abstinence, though heavy adolescent-onset use may produce more durable deficits ^[21].

Cultural considerations

• Standard cognitive screens have variable performance across languages, educational backgrounds, and cultures; the MoCA has been translated and validated in many languages, but interpretation requires culturally and educationally appropriate norms ^[17].
• Symptom expression of dementia varies cross-culturally; complaints of memory loss may be culturally normative or stigmatized, and family informants are essential ^[1].
• The diagnosis carries highly variable social meaning; advance care planning and disclosure preferences must be negotiated with the patient and family ^[2].

NCDs vary in trajectory by etiology, but several principles are general: progression in degenerative NCDs is measured in years, mortality is increased relative to age-matched peers, and the late stages are dominated by medical complications rather than primary cognitive symptoms.

Natural history by subtype

• Alzheimer disease typically progresses from mild NCD over 5–10 years to severe major NCD and death, with median survival from diagnosis of 4–8 years depending on age and comorbidity ^[3].
• Vascular NCD typically shows stepwise decline with discrete events, though small-vessel disease can mimic gradual decline; survival is often shorter than in AD due to cardiovascular mortality ^[5].
• Dementia with Lewy bodies often progresses more rapidly than AD, with median survival of 5–7 years from diagnosis and high burden of falls and hospitalization ^[6].
• Frontotemporal NCD has variable course depending on subtype; bvFTD often progresses faster than AD, while PPA may have prolonged plateau periods, with median survival of 6–11 years from onset ^[7].
• Parkinson disease dementia typically emerges 10 or more years after motor onset; survival from dementia diagnosis averages 4–5 years ^[6].
• Prion disease (sporadic CJD) typically progresses to death within 6–12 months of symptom onset ^[15].

Mild NCD outcomes

• Conversion to major NCD occurs in approximately 10–15% per year of patients with amnestic mild NCD in specialty clinics, though substantial proportions remain stable or revert to normal cognition ^[3].
• Biomarker positivity (amyloid and tau) increases the likelihood of progression to AD-type major NCD, while biomarker-negative mild NCD has a more variable outcome ^[3,19].

Functional outcomes

• Loss of independent IADLs (finances, medication management, transportation) typically precedes loss of basic ADLs (bathing, dressing, toileting) by years ^[2].
• Driving cessation, advance directive completion, and surrogate decision-maker identification should be addressed in mild NCD or early major NCD while capacity is intact ^[2].

Mortality

• Dementia is among the leading causes of death globally, with end-of-life mortality predominantly from pneumonia, dysphagia-related aspiration, and complications of immobility ^[8].
• Suicide risk is modestly elevated in early NCD (particularly in the period around diagnosis) and in those with comorbid depression; later stages carry lower suicide risk but higher risk of inanition and accidental death ^[22].

NCD intersects with the emergency setting through delirium, acute behavioral disturbance, suicide risk in early disease, wandering and elopement, and safety risks tied to medications, driving, and firearms.

Hospitalization criteria

• Acute behavioral disturbance that cannot be safely managed at home with adequate nonpharmacologic measures and a low-stimulation environment may warrant medical or psychiatric admission ^[25].
• Delirium superimposed on dementia is a medical emergency; admission focuses on identifying precipitants rather than psychiatric treatment per se ^[4].
• Suspected rapidly progressive dementia (course measured in weeks to months) warrants urgent inpatient evaluation for autoimmune, infectious, prion, neoplastic, and metabolic causes ^[12].
• Caregiver burnout with safety risk to patient or caregiver is a legitimate indication for respite admission or higher level of care ^[28].

Suicide risk

• Risk is highest in the first months after diagnosis and in patients with insight into their decline, comorbid depression, and access to means ^[22].
• Firearm access, stockpiling of medications, and recent loss of independence (driving, work, finances) are key risk markers ^[22].
• Assessment must adapt to cognitive level; collateral history is essential as patients with major NCD may underreport ideation or plans ^[22].

Agitation management

• First-line response is nonpharmacologic: identify and address pain, constipation, urinary retention, infection, sensory overload, unmet needs, and recent medication changes ^[25].
• If pharmacotherapy is required for acute agitation, low-dose oral atypical antipsychotics are preferred over IM administration when feasible; benzodiazepines are avoided except in withdrawal-related agitation ^[25].
• Restraints (physical or chemical) should be used only as a last resort, time-limited, and reviewed at short intervals; they independently worsen delirium and increase injury risk ^[4].

Driving and firearms

• All patients with diagnosed major NCD and many with mild NCD should undergo formal driving evaluation; jurisdictional reporting obligations vary ^[2].
• Firearm access should be assessed at diagnosis and in any patient with depressive symptoms, suicidal ideation, paranoia, or severe agitation; out-of-home storage is recommended in higher-risk situations ^[22].

NCD sits at the intersection of evolving biomarker science, contested disease-modifying therapeutics, and unresolved questions about how aggressively to screen, label, and treat.

Disease-modifying therapy for Alzheimer disease

• Anti-amyloid monoclonal antibodies (aducanumab, lecanemab, donanemab) have produced statistically significant slowing of cognitive decline in early AD trials, but the magnitude of clinical benefit, real-world generalizability, and ARIA risk continue to divide expert panels.^[19]
• Aducanumab received FDA accelerated approval in 2021 over the objection of its advisory committee and was subsequently withdrawn from the market in 2024; lecanemab and donanemab gained traditional approval in 2023 and 2024 respectively, but several payers and national health systems have restricted access.^[19]
• Selection criteria, infusion logistics, MRI surveillance burden, APOE-stratified bleeding risk, and out-of-pocket cost mean these agents are not yet broadly accessible.^[19]

Biomarker-defined Alzheimer disease

• The 2024 NIA-AA workgroup framework redefines Alzheimer disease as a biological entity diagnosed by amyloid and tau biomarkers, regardless of clinical status, broadening the population labeled with AD to include cognitively normal biomarker-positive adults.^[31]
• Critics argue that biomarker positivity in the absence of symptoms has uncertain prognostic value, risks overdiagnosis, and creates a population labeled with a disease for which no symptomatic treatment is indicated.^[31]

Screening asymptomatic adults

• The US Preventive Services Task Force finds insufficient evidence to recommend for or against cognitive screening of asymptomatic older adults in primary care, citing uncertain net benefit.^[32]
• Medicare's Annual Wellness Visit requires a cognitive assessment but does not specify a tool, leaving practice highly variable.^[32]

Behavioral symptoms and antipsychotics

• Despite the boxed warning and modest effect sizes, antipsychotics remain commonly prescribed for BPSD due to a paucity of effective alternatives.^[25]
• Brexpiprazole's 2023 FDA approval for AD-associated agitation introduced the first on-label option but did not resolve the underlying tension between modest benefit and class-wide harm.^[26]

Lewy body disease nomenclature

• A 2020 international consortium proposed unifying DLB, PD dementia, and PD without dementia under the umbrella of "Lewy body disease," arguing the one-year rule separating DLB from PDD is arbitrary; DSM-5-TR and most clinical guidelines have not adopted this framework.^[6]

CTE and repetitive head impact exposure

• Chronic traumatic encephalopathy is a neuropathologic diagnosis; clinical criteria (traumatic encephalopathy syndrome) have been proposed but remain research tools, and the prevalence and clinical-pathologic correlation of CTE in athletes and military personnel are actively contested.^[33]

Driving and capacity

• The threshold at which a mild NCD diagnosis should trigger driving restriction is contested across jurisdictions; formal on-road testing has the best evidence but is not universally available.^[2]

• DSM-5-TR replaced "dementia" with "major neurocognitive disorder" and introduced "mild neurocognitive disorder" to capture the prodromal stage; ICD-11 retains the term dementia.^[1]
• The two-domain shift between mild and major NCD is the criterion-A threshold: modest decline in one or more domains for mild NCD; substantial decline with loss of independence for major NCD.^[1]
• Delirium is defined by acute onset, fluctuating course, and disturbance of attention and awareness, distinguishing it from major NCD.^[1]
• The Confusion Assessment Method (CAM) is the most validated bedside delirium screen.^[16]
• Alzheimer disease is the most common cause of major NCD, accounting for roughly 60–80% of cases.^[2]
• Apolipoprotein E ε4 is the strongest common genetic risk factor for late-onset AD; one copy roughly triples and two copies roughly increase risk 8–12-fold.^[10]
• The pathognomonic clinical triad of DLB is fluctuating cognition, recurrent visual hallucinations, and spontaneous parkinsonism; REM sleep behavior disorder is a strong supportive feature.^[6]
• Severe neuroleptic sensitivity in DLB can precipitate irreversible parkinsonism and an NMS-like reaction; first-generation antipsychotics are contraindicated.^[6]
• Behavioral-variant frontotemporal dementia presents with early personality and behavioral change, disinhibition, apathy, and loss of empathy with relative memory sparing.^[7]
• Normal pressure hydrocephalus presents with the triad of gait apraxia, urinary incontinence, and cognitive impairment and is potentially reversible with shunting.^[14]
• Creutzfeldt-Jakob disease is characterized by rapidly progressive dementia, myoclonus, and a typical EEG with periodic sharp-wave complexes; MRI shows cortical ribboning and basal ganglia DWI hyperintensity.^[15]
• Cholinesterase inhibitors are first-line for mild-to-moderate Alzheimer disease and have evidence in DLB and Parkinson disease dementia, but not in frontotemporal NCD.^[18]
• Lecanemab and donanemab are FDA-approved disease-modifying therapies for early biomarker-confirmed AD, with ARIA-E and ARIA-H as defining adverse events.^[19]
• Acute behavioral worsening in a patient with known NCD is delirium until otherwise excluded.^[4]
• All antipsychotics carry a boxed warning for increased mortality in older adults with dementia-related psychosis.^[25]
• The Lancet Commission identifies 12 modifiable risk factors potentially accounting for up to 40% of dementia cases, including hypertension, hearing loss, smoking, obesity, depression, physical inactivity, diabetes, low education, social isolation, excessive alcohol, traumatic brain injury, and air pollution.^[8]

No external funding. No conflicts of interest declared. Peer-review status: pending.