Advances in the Diagnosis of Early Alzheimer's Dementia and Mild Cognitive Impairment

Advances in the Diagnosis of Early Alzheimer's Dementia and Mild Cognitive Impairment Fifteen–Twenty High-Yield Points Concept and definitions

Mild cognitive impairment (MCI) and cognitive impairment, not dementia (CIND) describe measurable cognitive deficits that do not impair daily function. Loss of functional ability due to impaired cognition is the single feature that separates dementia from MCI.

Just over 20% of people aged 71 and above have cognitive impairment without dementia. 15–20% of those with MCI or CIND convert to dementia each year.

Normal ageing may produce slowed thinking and reaction time, mild recent memory loss and impaired executive function, which may or may not progress. Old age alone never causes dysfunctional cognitive impairment.

Three questions establish the cause of confusion: (i) Has the onset been acute (hours to days)? (ii) Are physical factors (illness, drugs, sensory deprivation) contributing? (iii) Are psychological factors (depression, psychosis) contributing? These target the treatable causes.

Onset and rate of progression are the most valuable historical items. Sudden onset over days means delirium; gradual decline over months to years means degenerative dementia; irregular stepwise decrements favour multi-infarct dementia.

The Mini-Cog is a useful screening tool: it combines three-item recall (memory) with clock drawing (executive function). Executive dysfunction is critical because it determines the ability to perform IADLs.

Cognition should be assessed by taking separate histories from the patient and an informant. Patients with pathological memory impairment typically report no complaints, while relatives report and worry about the loss.

Other validated bedside instruments include the MMSE, MoCA, and SLUMS. Education level must be considered when interpreting scores — particularly important in the Indian setting, where illiteracy demands vernacular and education-adjusted tools.

Mood and affect must be assessed throughout. Depression, apathy, emotional lability, agitation and aggression are common and, if missed, lead to misdiagnosis.

Formal neuropsychological testing by an experienced psychologist is indicated when the diagnosis is uncertain, in the very intelligent or poorly educated, and when depression is suspected.

Minimum work-up: focused history and examination (screening for delirium and depression, identifying sensory impairment), functional status assessment, mental status examination, and selected laboratory studies to exclude reversible causes. Brain imaging should not be done automatically in every patient.

Detecting the presymptomatic phase on clinical grounds alone is difficult, although accelerated long-term forgetting may be an early indicator.

Current diagnostic criteria therefore require biomarkers reflecting the three core features: β-amyloid, phosphorylated tau, and neurodegeneration.

These can be measured by neuroimaging (amyloid PET, tau PET, MRI) and in CSF (Aβ1-42, phosphorylated tau, neurofilament light).

Blood-based biomarkers — plasma Aβ42/40 ratio, phosphorylated tau, and neurofilament light — have become increasingly viable with improvements in assay sensitivity, with major implications for facilitating early diagnosis.

Structural MRI supports early diagnosis: hippocampal and medial temporal atrophy favours AD; the pattern of atrophy also helps separate AD from vascular and other dementias.

Functional imaging refines the differential: dopamine transporter (loflurane) SPECT is normal in AD but abnormal in Lewy body dementia; 123I-MIBG cardiac scintigraphy may distinguish DLB from AD.

Electrophysiology: altered cortical synaptic plasticity in response to 5-Hz repetitive TMS has been described as a marker in amnestic MCI converting to AD.

Even after diagnosis, no intervention has been proven to prevent progression from MCI to dementia; screening is justified because it allows longitudinal follow-up and structured support and education of patients and families.