Alzheimer's Disease: 7 Stages, Treatments, and 2023 Advances

Six Million Americans. One Disease.

Alzheimer's disease is the sixth leading cause of death in the United States, affecting an estimated 6.7 million Americans aged 65 and older as of 2023, according to the Alzheimer's Association. By 2050, that number is projected to nearly double to 12.7 million unless prevention or treatment breakthroughs change the trajectory. The disease costs the U.S. economy approximately $345 billion annually in direct medical and long-term care expenses — a figure that excludes the unpaid labor of 11 million family caregivers.

The Amyloid-Tau Cascade

Alzheimer's pathology centers on two proteins that become toxic when misfolded. Amyloid-beta peptides — fragments cleaved from the amyloid precursor protein (APP) — aggregate into plaques between neurons. Tau protein, which normally stabilizes microtubule structures inside neurons, becomes hyperphosphorylated and forms neurofibrillary tangles within cells. The amyloid cascade hypothesis, first articulated by John Hardy and Gerald Higgins in 1992, holds that amyloid accumulation triggers the downstream tau pathology that directly drives neuronal death.

This sequence begins silently. PET imaging studies show amyloid deposition occurring 15–20 years before first clinical symptoms. Tau pathology spreads in a predictable spatial pattern described by Braak staging (stages I–VI), beginning in the entorhinal cortex and hippocampus before invading association cortices.

The 7-Stage GDS Framework

The Global Deterioration Scale (GDS), developed by Barry Reisberg at NYU, provides clinicians and caregivers a standardized framework for tracking disease progression.

Lecanemab: The 2023 FDA Approval

In January 2023, the FDA granted traditional approval to lecanemab (brand name Leqembi), developed by Eisai and Biogen. The CLARITY AD phase 3 trial enrolled 1,795 patients with early-stage Alzheimer's and found that 10 mg/kg intravenous infusion every two weeks slowed clinical decline by 27% on the Clinical Dementia Rating-Sum of Boxes (CDR-SB) scale, and reduced amyloid burden by approximately 50 centiloids over 18 months. The drug's measurable real-world impact on day-to-day function — approximately 18% slowing relative to placebo on composite clinical measures — marks the first confirmed disease-modifying effect in Alzheimer's history.

• Eligibility: Patients must confirm amyloid positivity via PET scan or cerebrospinal fluid biomarkers before starting treatment
• Cost: Listed at $26,500 per year; Medicare coverage was finalized in 2023 for amyloid-confirmed early-stage patients
• Mechanism: Lecanemab binds preferentially to soluble amyloid protofibrils, the most toxic amyloid species, rather than insoluble plaques
• Companion approval: Donanemab (Eli Lilly) received FDA approval in July 2024, offering an alternative with quarterly dosing after amyloid clearance

ARIA: The Critical Side Effect

Amyloid-related imaging abnormalities (ARIA) are the most clinically significant safety concern with anti-amyloid therapies. In the CLARITY AD trial, ARIA occurred in 21.5% of lecanemab-treated patients compared to 9.5% on placebo. Two subtypes occur:

• ARIA-E (edema/effusion): Temporary fluid accumulation in or around the brain, usually asymptomatic but occasionally causing headache, confusion, or vision changes
• ARIA-H (microhemorrhages/siderosis): Small bleeds detectable on MRI; rarely symptomatic but may increase in frequency and size

APOE ε4 carriers — who already face 3- to 8-fold increased Alzheimer's risk — also have significantly higher ARIA rates on lecanemab (35.9% in homozygotes vs. 19.7% in non-carriers). All patients require baseline MRI and periodic monitoring scans throughout treatment.

Existing Symptomatic Medications

Risk Reduction: What Evidence Supports

The FINGER trial, a 2015 Finnish randomized controlled trial of 1,260 older adults at dementia risk, demonstrated that a multidomain lifestyle intervention — combining diet, exercise, cognitive training, and vascular risk management — improved cognitive performance by 25% vs. a control group at two years. Specifically, the following lifestyle factors have population-level evidence:

• Aerobic exercise (150 minutes/week) reduces Alzheimer's risk by approximately 30–35% in prospective studies
• Treating hypertension reduces dementia incidence; the SPRINT MIND trial showed 19% relative risk reduction with intensive blood pressure control
• Hearing loss treatment: individuals fitted with hearing aids showed significantly less cognitive decline in the ACHIEVE trial (2023)
• Social engagement and formal education — each additional year of schooling associated with ~7% reduced dementia risk

This article is for informational purposes only. Consult a qualified healthcare professional.