The hallmark brain changes in Alzheimer's disease are?

• A. Amyloid plaques and neurofibrillary tangles
• B. Lewy bodies
• C. Demyelination
• D. Gliosis

Answer: (A)

Extracellular amyloid plaques and intracellular neurofibrillary tangles are the hallmark brain changes of Alzheimer's disease. These two lesions define the classic pathology: beta-amyloid–containing plaques build up outside neurons, while tau protein becomes hyperphosphorylated and forms tangles inside neurons, leading to synaptic dysfunction and neuron loss that drive cognitive decline. This combination is distinctive for Alzheimer's and is what researchers and clinicians look for when understanding and diagnosing the disease.

Lewy bodies are characteristic of Lewy body dementia and Parkinson’s disease with dementia, not Alzheimer's. Demyelination occurs in conditions like multiple sclerosis, not as the defining feature of Alzheimer's. Gliosis is a general reactive change in glial cells seen in many CNS injuries and diseases, but it is not the defining lesion that distinguishes Alzheimer's disease.