Early Alzheimer's disease is commonly associated with atrophy in which brain region?

• A. Lateral occipital lobe atrophy.
• B. Global ventricular enlargement without regional atrophy.
• C. Frontal lobe atrophy with temporal involvement.
• D. Medial temporal lobe atrophy on MRI and temporoparietal hypometabolism on PET.

Answer: (D)

Early Alzheimer's disease disrupts memory networks first, so imaging often shows structural loss in the medial temporal lobe, especially areas around the hippocampus, on MRI. This medial temporal atrophy reflects early neuron loss in regions crucial for forming and retrieving new memories. At the same time, functional imaging with PET reveals reduced glucose metabolism in the temporoparietal cortex, aligning with dysfunction in the broader posterior cortical network that supports higher-order processing and memory integration. The combination of medial temporal lobe atrophy and temporoparietal hypometabolism is a classic pattern for early AD, tying together the memory impairment with the network-wide metabolic changes seen on PET.

Other patterns don’t fit early AD as cleanly: atrophy confined to the lateral occipital lobe isn’t typical of early AD and is more linked to visual or posterior cortical syndromes; global enlargement of the ventricles without regional atrophy is nonspecific and can occur with aging or various conditions; frontal lobe atrophy with temporal involvement points more toward frontotemporal dementia, which has a different clinical and imaging profile.