Dementia is a broad term for a group of symptoms affecting memory, thinking, and social function severely enough to interfere with daily life. Alzheimer's disease is the most common cause of dementia, accounting for 60–80% of cases and affecting an estimated 6.7 million Americans over age 65. It is a progressive neurodegenerative disease characterized by the abnormal accumulation of amyloid plaques and tau tangles in the brain, leading to the progressive death of neurons and irreversible cognitive decline.
MRI plays a central role in the evaluation of dementia — identifying the characteristic brain atrophy pattern of Alzheimer's disease, excluding surgically treatable causes such as normal pressure hydrocephalus and subdural hematoma, and distinguishing Alzheimer's from vascular dementia driven by chronic small vessel ischemia and stroke. An accurate diagnosis is the essential first step — different dementia types have different treatments, different prognoses, and different implications for family members.
Causes
Alzheimer's disease
The hallmarks of Alzheimer's disease are the extracellular buildup of amyloid-beta plaques between neurons and the intracellular accumulation of neurofibrillary tangles of hyperphosphorylated tau protein within neurons — together disrupting synaptic function, triggering neuroinflammation, and causing progressive neuronal death. The disease begins in the hippocampus and entorhinal cortex — the brain's primary memory encoding structures — producing the characteristic early memory impairment before spreading to association cortices. Age is the greatest risk factor, with prevalence doubling approximately every five years after age 65. The APOE ?4 allele is the strongest genetic risk factor for late-onset Alzheimer's, present in approximately 40% of patients.
Other causes of dementia
Vascular dementia results from cumulative cerebrovascular injury — strokes and chronic small vessel ischemic disease — and produces stepwise or gradual cognitive decline with prominent executive dysfunction. Lewy body dementia is caused by abnormal alpha-synuclein deposits and presents with a characteristic triad of fluctuating cognition, visual hallucinations, and Parkinsonism — with high sensitivity to antipsychotic medications. Frontotemporal dementia (FTD) causes personality, behavior, and language changes in patients typically aged 45–65 — younger than typical Alzheimer's onset. Mixed dementia combining Alzheimer's and vascular pathology is increasingly recognized as the most common dementia subtype in autopsy studies. Potentially reversible causes — normal pressure hydrocephalus, thyroid disease, vitamin B12 deficiency, and chronic infections — must always be excluded.
Symptoms
Symptoms differ by dementia type but share the common feature of progressive cognitive and functional decline:
- Early Alzheimer's disease: Short-term memory loss is the hallmark — forgetting recently learned information, repeating questions, misplacing items, and difficulty retaining new experiences. Older, remote memories are typically preserved early. Word-finding difficulty and mild disorientation emerge as the disease progresses.
- Moderate Alzheimer's disease: Language difficulties, spatial disorientation, poor judgment, personality and behavioral changes (anxiety, depression, agitation), and inability to manage complex daily tasks such as finances and medications.
- Late Alzheimer's disease: Loss of ability to communicate meaningfully, recognize family members, and perform basic activities of daily living — requiring full-time care.
- Vascular dementia: More prominent executive dysfunction and processing speed slowing, with stepwise decline often temporally related to vascular events. Gait disturbance is common early.
- Lewy body dementia: Fluctuating alertness (with marked variability hour to hour), recurrent detailed visual hallucinations, REM sleep behavior disorder, and Parkinsonism — often confused with Alzheimer's but requiring different management.
Diagnosis
A comprehensive evaluation includes detailed clinical history from both patient and informant, validated cognitive screening tools (MoCA, MMSE), and a thorough neurological examination assessing all cognitive domains. Standardized neuropsychological testing characterizes the pattern of impairment across memory, language, attention, visuospatial function, and executive function — providing the foundation for differential diagnosis.
MRI is the essential structural imaging study in every dementia evaluation. In Alzheimer's disease, MRI demonstrates disproportionate hippocampal and medial temporal lobe atrophy — quantified using hippocampal volumetry compared to age-matched normative databases. The medial temporal atrophy (MTA) scale provides a standardized visual rating. MRI also identifies white matter lesions from vascular disease, cortical infarcts from stroke, the characteristic ventricular pattern of normal pressure hydrocephalus, and subdural collections — all of which alter diagnosis and management.
PET imaging with amyloid tracers (florbetapir, florbetaben, flutemetamol) directly visualizes amyloid plaque burden in the brain — a positive scan confirms Alzheimer's pathology while a negative scan effectively excludes it. FDG-PET shows characteristic patterns of reduced glucose metabolism in temporoparietal cortex in Alzheimer's disease. Blood-based biomarkers (plasma amyloid, phospho-tau 217) are emerging as accessible screening tools to identify candidates for further workup. CSF analysis of amyloid-beta 42, total tau, and phospho-tau provides high accuracy biological confirmation of Alzheimer's pathology.
Dementia Classification
Dementia is classified by underlying cause, which guides treatment, prognosis, and family counseling:
- Alzheimer's Disease: Most common (60–80%) — amyloid and tau pathology with predominant episodic memory impairment and hippocampal atrophy on MRI.
- Vascular Dementia: Caused by cerebrovascular disease — stroke and small vessel ischemia. Executive dysfunction prominent. Managed with aggressive vascular risk factor control.
- Lewy Body Dementia: Fluctuating cognition, visual hallucinations, Parkinsonism, and REM sleep disorder. High antipsychotic sensitivity — certain medications that are safe in Alzheimer's can be life-threatening in Lewy body dementia.
- Frontotemporal Dementia: Predominantly behavioral or language changes — typically younger onset (45–65). Memory relatively preserved early. Tau or TDP-43 pathology.
- Normal Pressure Hydrocephalus: A potentially reversible cause — gait disturbance, incontinence, and cognitive impairment that may respond dramatically to CSF shunting.
Treatments
While there is no cure for Alzheimer's disease, treatments can manage symptoms and — with newer disease-modifying therapies — meaningfully slow the rate of cognitive decline when initiated early.
Symptomatic pharmacotherapy:
Cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and memantine are the standard symptomatic treatments for Alzheimer's disease, modestly improving cognition, daily function, and behavioral symptoms. They do not halt disease progression but can meaningfully improve quality of life and delay functional decline. Donepezil is also approved for severe Alzheimer's disease.
Disease-modifying therapy (anti-amyloid therapies):
Lecanemab (Leqembi) and donanemab have received regulatory approval for early symptomatic Alzheimer's disease — specifically for mild cognitive impairment (MCI) due to Alzheimer's and mild Alzheimer's dementia with confirmed amyloid pathology. Both agents clear amyloid plaques from the brain and have demonstrated statistically significant slowing of cognitive and functional decline in large clinical trials. MRI monitoring for amyloid-related imaging abnormalities (ARIA) — including brain microhemorrhages and edema — is required during treatment, making ongoing neuroimaging an essential component of care.
Non-pharmacological and supportive care:
Cognitive stimulation, structured daily routine, physical activity, and sleep hygiene are essential non-pharmacological interventions with meaningful evidence of benefit. Managing behavioral symptoms — agitation, depression, anxiety, psychosis, and sleep disturbance — with behavioral strategies first and targeted medications when necessary significantly improves quality of life for both patients and caregivers. Early legal, financial, and advance care planning after diagnosis allows patients to participate in decisions while cognitive capacity is preserved.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Brain MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.