Which pathology is characteristic of Alzheimer's disease?

• A. Neurofibrillary tangles and amyloid plaques in the brain.
• B. Loss of dopaminergic neurons in the substantia nigra.
• C. Demyelination of optic nerve.
• D. Degeneration of cerebellar Purkinje cells.

Answer: (A)

Neurofibrillary tangles and amyloid plaques in the brain are characteristic of Alzheimer's disease. The plaques are extracellular aggregates of beta-amyloid peptide that accumulate in cortex and hippocampus, disrupting synaptic signaling and triggering inflammatory responses. The tangles are intracellular bundles of hyperphosphorylated tau protein that destabilize microtubules, impairing axonal transport and leading to neuronal death. The spread and density of these lesions in memory-related regions, especially the hippocampus and surrounding cortices, explain the progressive memory loss and cognitive decline seen in Alzheimer's. These features set Alzheimer's apart from other conditions that affect the brain.

For contrast, dopaminergic neuron loss in the substantia nigra is typical of Parkinson disease and underlies motor symptoms; optic nerve demyelination is associated with optic neuritis or multiple sclerosis; and Purkinje cell degeneration is linked to cerebellar ataxias.