Major Neurocognitive Disorder Due to Alzheimer’s Disease

Clinical picture

• Episodic memory fails first, with repeated questions, misplaced objects, growing reliance on notes and family, and rapid forgetting of recent conversations.
• Word-finding pauses, semantic paraphasias, and impoverished conversation follow, alongside visuospatial errors and getting lost on familiar routes.
• Executive decline appears as poor financial judgment, missed bills, unsafe driving, and vulnerability to scams long before basic self-care is lost.
• Insight is limited and often absent, so families rather than patients report the decline while patients minimize or confabulate around the gaps.
• Neuropsychiatric symptoms affect up to 90% over the course: apathy earliest, then depression, agitation, delusions of theft, and evening sundowning.
• Function declines in a predictable order, from instrumental tasks such as cooking and medications down to dressing, feeding, and continence.

Criteria snapshot

• Major neurocognitive disorder requires significant decline in one or more cognitive domains, established by informant report plus objective standardized testing.
• The deficits interfere with independence in everyday activities, meaning the person needs assistance with tasks such as paying bills or managing medications.
• Deficits do not occur exclusively during an episode of delirium and are not better explained by another mental disorder such as major depression.
• Probable Alzheimer's requires a causative genetic mutation, or all of clear memory decline, steady gradual progression, and no evidence of mixed etiology.
• Specify with or without behavioral disturbance and rate severity as mild, moderate, or severe according to the level of daily assistance required.

Neurobiology

• Extracellular amyloid-beta plaques and intracellular hyperphosphorylated tau tangles spread outward from entorhinal cortex and hippocampus along Braak stages.
• Cholinergic neuron loss in the nucleus basalis of Meynert underlies the memory deficit and provides the rationale for cholinesterase inhibitor therapy.
• APOE e4 raises risk roughly 3-fold with one allele and 8-12 fold with two, while APP, PSEN1, and PSEN2 mutations cause autosomal dominant early-onset disease.
• CSF and plasma biomarkers show low amyloid-beta 42 with elevated phosphorylated tau 181 or 217, and amyloid or tau PET confirms pathology in living patients.
• MRI shows medial temporal and hippocampal atrophy, and FDG-PET shows temporoparietal and posterior cingulate hypometabolism with sparing of primary cortex.
• Modifiable risks including hypertension, diabetes, obesity, smoking, hearing loss, depression, and low education account for roughly 40% of population risk.

Psychology

• Excess disability arises when caregivers over-assist or environments overwhelm, producing more observed impairment than the underlying pathology dictates.
• Agitation is usually communication of unmet need, whether pain, boredom, fear, or overstimulation, and responds to antecedent-based behavioral analysis.
• Preserved procedural and emotional memory allows habit routines, familiar music, and demonstration to work when explicit verbal instruction fails.
• Catastrophic reactions follow demands that exceed residual capacity, so simplifying tasks and reducing the number of choices reliably restores calm.
• Caregiver depression affects 30-40%, and measured caregiver burden predicts nursing home placement more strongly than the patient's cognitive score.

Differential & comorbidity

• Distinguish from delirium by the acute onset, fluctuating attention, and identifiable medical trigger, remembering that the two conditions frequently coexist.
• Vascular disease shows stepwise decline with infarcts, while Lewy body disease brings visual hallucinations, parkinsonism, REM sleep behavior disorder, and fluctuation.
• Frontotemporal dementia usually presents before age 65 with disinhibition, apathy, or progressive language loss, with episodic memory relatively spared early.
• Screen reversible contributors including B12 deficiency, hypothyroidism, normal pressure hydrocephalus, subdural hematoma, and total anticholinergic burden.
• Depression can mimic dementia with poor effort and do-not-know answers, and it also commonly coexists, so an adequate antidepressant trial is warranted.

Pharmacologic treatment

• Donepezil 5-10 mg/day, rivastigmine patch, or galantamine give modest symptomatic benefit; GI upset, bradycardia, and vivid dreams are common effects.
• Memantine 10 mg twice daily is added at moderate to severe stages as an NMDA antagonist, generally better tolerated than cholinesterase inhibitors.
• Anti-amyloid monoclonals lecanemab and donanemab modestly slow early-stage decline but require APOE genotyping and serial MRI monitoring for ARIA.
• Avoid antipsychotics where possible given the boxed warning for increased mortality in dementia; brexpiprazole is FDA-approved for agitation in Alzheimer's.
• Deprescribe anticholinergics, benzodiazepines, and sedative-hypnotics, which worsen cognition and fall risk far more than they improve behavior.

Psychotherapy

• Cognitive stimulation therapy, delivered as 14 group sessions over 7 weeks, produces cognitive and quality-of-life gains rivaling cholinesterase inhibitors.
• Reminiscence therapy and structured life review improve mood, engagement, and communication in the mild to moderate stages of the illness.
• Behavioral activation and problem-solving therapy adapted for mild impairment treat comorbid depression without adding medication burden.
• Caregiver skills training such as the REACH II protocol reduces caregiver depression and measurably delays institutional placement.
• Person-centered communication training, meaning short sentences, one instruction at a time, and no quizzing, reduces resistance during personal care.

Adjunct options

• Stage and track decline with the MoCA or MMSE plus a functional measure, repeating every 6-12 months to document the individual trajectory.
• Environmental measures matter: consistent routine, daylight exposure, labeled rooms, reduced clutter, and nighttime safeguards against wandering.
• Address driving, firearms, finances, and wandering explicitly and early, and complete advance directives and surrogate decision-making while capacity remains.
• Exercise, hearing aids, blood pressure control, and sustained social engagement slow functional decline and reduce neuropsychiatric symptom burden.
• Connect families to adult day programs, respite care, the Alzheimer's Association helpline, and palliative or hospice services in the late stages.

Clinical pearls

• The informant, not the patient, provides the diagnostic history.
• Any acute change in a dementia patient is delirium until proven otherwise.
• Behavior is communication: look for pain, infection, or overstimulation first.