Question

Which of the following statements is NOT true about prion disease?

• A. About 10% of patients have myoclonus
• B. It is caused by an infectious protein
• C. Dementia is a universal feature
• D. Brain biopsy is diagnostic

Hint:

Myoclonus is far more common than 10% in prion disease, and dementia, though typical, is not seen in every case or every prion disease.

Answer 1

The Correct Option is A, C

Step 1: Recall what a prion disease is.
Prion diseases (such as Creutzfeldt-Jakob disease, CJD) are caused by an abnormally folded, infectious form of a normal cell surface protein called PrP. This misfolded protein (PrPSc) converts normal PrP into more of the abnormal form, without any DNA or RNA involved. So the statement that it is caused by an infectious protein is TRUE.

Step 2: Check the myoclonus figure.
Myoclonus (sudden brief muscle jerks) is a very common finding in CJD, seen in the large majority of patients, commonly quoted at around 80 to 90% at some point in the illness, not just 10%. So "about 10% have myoclonus" understates how common it is and is NOT a true statement.

Step 3: Check the dementia claim.
Rapidly progressive dementia is the hallmark of classic CJD, but calling it a strictly universal feature across all prion diseases overreaches. Some prion diseases, and even some early or atypical CJD presentations, are dominated by ataxia, visual disturbance, or behavioral change before dementia becomes obvious, and a few variants (like fatal familial insomnia) present mainly with sleep and autonomic disturbance rather than dementia as the leading feature. So calling dementia "universal" is NOT strictly true.

Step 4: Check the brain biopsy claim.
Brain biopsy showing spongiform change, neuronal loss, and gliosis is the definitive way to confirm the diagnosis while the patient is alive, so this statement is TRUE (biopsy is diagnostic, even though it is rarely done because of the risk of prion transmission to instruments and staff).

Step 5: Put together the false statements.
The two statements that are NOT true are the 10% myoclonus figure (it is much higher) and calling dementia a universal feature (it is common but not invariable across all prion diseases).
\[ \boxed{\text{10\% have myoclonus AND dementia is universal (both NOT true)}} \]