PML is caused by –
**Core Concept**
Progressive multifocal leukoencephalopathy (PML) is a rare and often fatal viral disease characterized by progressive damage to the white matter of the brain at multiple locations. It is caused by a **demyleinating disease** due to a viral infection. The underlying principle involves **JC virus** reactivation.
**Why the Correct Answer is Right**
The correct answer is related to the JC virus, a type of **polyomavirus** that typically infects most people during childhood but remains dormant. In individuals with weakened immune systems, such as those with HIV/AIDS or taking immunosuppressive drugs, the JC virus can reactivate and cause PML. The virus targets **oligodendrocytes**, leading to demyelination.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the specific virus is not identified.
**Option B:** Incorrect as it is not related to the JC virus.
**Option C:** Incorrect because, although it might be related to viral infections, it is not the specific cause of PML.
**Option D:** Incorrect as it does not specify the JC virus.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that PML is a complication of immunosuppression, and its diagnosis should be considered in patients with **HIV/AIDS** or those on **immunomodulatory therapies** presenting with neurological symptoms.
**Correct Answer:** D. JC virus.