A 54 year old white male presents with gradual onset of mild dementia, ataxic gait, and stale myoclonus. An MRI scan is normal, and an examination of his cerebrospinal fluid reveals no abnormalities, but the patient’s EEG is remarkable for recurrent bursts of high-voltage slow waves. Over the next 6 months, the patient’s dementia rapidly worsens, accompanied by general hypeonicity and profound dysahria. The patient dies sholy thereafter. Which of the following is the mostly likely neuropathological finding on autopsy?

## **Core Concept**
The patient's presentation suggests a prion disease, specifically Creutzfeldt-Jakob disease (CJD), which is a rare, degenerative, fatal brain disorder. CJD is characterized by a rapid progression of dementia, ataxia, and myoclonus. The diagnosis is often confirmed by the presence of a distinctive electroencephalogram (EEG) pattern and neuropathological findings.

## **Why the Correct Answer is Right**
The correct answer, **C. Prion protein (PrP) accumulation**, is right because CJD is caused by the accumulation of abnormally folded prion protein (PrP) in the brain. This abnormal protein leads to neuronal degeneration and the characteristic clinical and pathological features of the disease. The patient's symptoms, such as gradual onset of dementia, ataxic gait, myoclonus, and a rapidly worsening course, are consistent with CJD. The EEG finding of recurrent bursts of high-voltage slow waves is also typical for CJD.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Alzheimer's disease pathology primarily involves amyloid-beta plaques and neurofibrillary tangles, not prion protein accumulation. While Alzheimer's can present with dementia, the rapid progression and specific EEG findings point away from this diagnosis.
- **Option B:** Parkinson's disease pathology involves Lewy bodies and a deficiency in dopamine, primarily affecting motor function. Although there can be some cognitive decline, the acute presentation and EEG findings do not align with Parkinson's.
- **Option D:** Huntington's disease is characterized by an autosomal dominant inheritance pattern, chorea, and specific neuropathological changes including neuronal loss in the basal ganglia. The clinical presentation does not match the described case.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Creutzfeldt-Jakob disease often presents with a rapidly progressive dementia, myoclonus, and a distinctive EEG pattern. A helpful mnemonic is **CJ** for **Creutzfeldt-Jakob** being associated with **Characteristic EEG changes** and **Jolts** (myoclonus).

## **Correct Answer:** C. Prion protein (PrP) accumulation

✓ Correct Answer: B. Diffuse spongiform change