PML is caused by
**Core Concept**
Progressive Multifocal Leukoencephalopathy (PML) is a rare and often fatal demyelinating disease of the central nervous system (CNS). It is characterized by the destruction of oligodendrocytes, the myelinating cells of the CNS, leading to demyelination and axonal damage.
**Why the Correct Answer is Right**
PML is caused by the reactivation of the JC virus (JCV), a polyomavirus that typically remains latent in the body. The virus selectively infects and destroys oligodendrocytes, leading to the characteristic demyelinating lesions. This occurs particularly in individuals with compromised immune systems, such as those with HIV/AIDS, lymphoproliferative disorders, or receiving immunosuppressive therapy.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PML is not caused by a bacterial infection, such as Lyme disease or syphilis.
**Option B:** This option is incorrect because while certain viral infections, such as CMV and EBV, can affect the CNS, they do not cause PML.
**Option C:** This option is incorrect because Creutzfeldt-Jakob disease (CJD) is a prion disease, not a viral infection like PML.
**Clinical Pearl / High-Yield Fact**
PML is often associated with immunosuppression, particularly in patients with HIV/AIDS. The diagnosis of PML is typically made by MRI and CSF analysis, showing demyelinating lesions and the presence of JCV DNA.
**Correct Answer:** D. JC virus