**Core Concept**
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by the accumulation of tau protein in the brain, leading to the death of neurons in the brainstem, particularly in the midbrain and pons. This results in a range of symptoms, including difficulty with eye movements, balance, and coordination.

**Why the Correct Answer is Right**
PSP is a progressive disorder, meaning that the symptoms worsen over time. The hallmark symptom of PSP is difficulty with vertical eye movements, particularly upward gaze. This is due to the involvement of the posterior commissure, a structure in the midbrain that plays a critical role in eye movements. The accumulation of tau protein in the brain also leads to the degeneration of neurons in the basal ganglia, which can cause parkinsonian symptoms such as rigidity and bradykinesia.

**Why Each Wrong Option is Incorrect**
**Option A:** PSP is actually characterized by a lack of significant cognitive decline, unlike Alzheimer's disease. Therefore, this statement is incorrect.

**Option B:** PSP is indeed a tauopathy, and the accumulation of tau protein in the brain is a hallmark of the disease. Therefore, this statement is correct, but it is one of the options, so we must continue.

**Option C:** PSP is actually characterized by a lack of significant cognitive decline, unlike frontotemporal dementia. Therefore, this statement is incorrect.

**Option D:** PSP is indeed a progressive disorder, and the symptoms worsen over time. Therefore, this statement is correct, but it is one of the options, so we must continue.

**Clinical Pearl / High-Yield Fact**
One key feature of PSP is the presence of a "supranuclear" gaze palsy, which means that the eye movements are impaired due to a problem with the neural signals that control the muscles, rather than a problem with the muscles themselves.

**Correct Answer: A. PSP is actually characterized by a lack of significant cognitive decline, unlike Alzheimer's disease.**