## Core Concept
Subcortical dementia refers to a type of dementia characterized by damage to the subcortical structures of the brain, which include areas beneath the cerebral cortex such as the basal ganglia, thalamus, and brainstem. This type of dementia often presents with distinct clinical features compared to cortical dementia, including prominent motor symptoms, changes in personality, and cognitive slowing.

## Why the Correct Answer is Right
The correct answer, which involves understanding which condition is not typically associated with subcortical dementia, requires knowledge of the neuropathological features of various dementias. Subcortical dementias are commonly seen in conditions that affect the subcortical regions of the brain, such as Parkinson's disease, Huntington's disease, and progressive supranuclear palsy. Alzheimer's disease, on the other hand, is primarily considered a cortical dementia, although it can have subcortical features, especially in advanced stages.

## Why Each Wrong Option is Incorrect
- **Option A:** Conditions like Parkinson's disease are known to cause subcortical dementia due to their primary impact on subcortical structures.
- **Option B:** Huntington's disease is another classic cause of subcortical dementia, characterized by significant degeneration in the basal ganglia.
- **Option C:** Progressive supranuclear palsy (PSP) is a tauopathy that affects subcortical regions and is associated with subcortical dementia.

## Why the Correct Answer (D) is Correct and Others are Incorrect
- **Option D:** Alzheimer's disease is primarily a cortical dementia. It is characterized by amyloid plaques, neurofibrillary tangles, and neuronal loss mainly in the cerebral cortex. While Alzheimer's can have subcortical involvement, especially in advanced stages, it is not classified as a subcortical dementia.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that subcortical dementias often present with more pronounced motor symptoms and changes in mood and personality early in the disease course, in contrast to cortical dementias, which typically present with prominent memory and language impairments early on. Recognizing these patterns can help in diagnosing the underlying cause of dementia.

## Correct Answer: D. Alzheimer's disease.