Alzheimer's Disease: Overview

Alzheimer's disease unfolds through three distinct stages: preclinical, mild cognitive impairment (MCI), and dementia. The preclinical stage occurs before symptoms appear, MCI involves noticeable cognitive decline that doesn't severely impair daily function, and dementia represents advanced memory loss and cognitive dysfunction. Progression is gradual and insidious, with each stage reflecting increasing neuronal damage.

Amyloid plaques are extracellular accumulations of Aβ protein, while neurofibrillary tangles consist of tau protein inside neurons. These pathological hallmarks induce neuronal dysfunction and death through synaptic impairment, excitotoxicity, oxidative stress, and neuroinflammation. Together, they trigger cholinergic neuron loss and widespread cognitive decline characteristic of Alzheimer's disease.

The most significant neurochemical disturbance in Alzheimer's disease is a deficiency in acetylcholine (ACh), stemming from atrophy and degeneration of subcortical cholinergic neurons. Additionally, reduced levels of serotonin and norepinephrine occur. These neurotransmitter deficiencies contribute to cognitive impairment, behavioral symptoms, and mood disturbances observed in affected patients.

Cerebrospinal fluid biomarkers include changes in Aβ and tau proteins, which are increasingly incorporated into diagnostic criteria. Imaging biomarkers such as hippocampal atrophy and cortical hypometabolism also play crucial roles in confirming diagnosis. These objective markers, combined with clinical evaluation and neuropsychological assessment, provide comprehensive diagnostic confirmation.

Gene mutations in APP, PSEN1, and PSEN2 can trigger early-onset Alzheimer's disease with autosomal dominance, meaning inheriting one mutated copy from either parent causes disease development. These genetic mutations lead to abnormal amyloid and tau protein accumulation, accelerating neurodegeneration. Early-onset AD typically appears before age 65 and progresses more rapidly than late-onset forms.

Cholinesterase inhibitors manage behavioral symptoms by preventing acetylcholine breakdown, increasing available acetylcholine levels in the brain. This compensates for the acetylcholine deficiency caused by cholinergic neuron loss. Current treatments prioritize symptom relief and disease progression deceleration, with cholinesterase inhibitors and memantine (Namenda) serving as primary pharmacological agents.

Behavioral and psychiatric symptoms common in Alzheimer's disease are managed using cholinesterase inhibitors, serotonergic antidepressants, or atypical antipsychotics. These medications address mood disturbances, agitation, and behavioral changes resulting from neurochemical imbalances. Serotonergic antidepressants drugs tricyclics ssris and snris are among the pharmacological options available for symptom management.