This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Pathology
Progressive multifocal leukoencephalopathy spares 
Select and explain. 
A. White matter of cerebrum, B. White matter of parietal lobe, C. White matter of periventricular area, D. Spinal cord and optic nerve
D: Spinal cord and optic nerve
Answer: D: Spinal cord and optic nerve 
Explanation: Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease which results from the reactivation of John Cunningham virus (JC virus) infecting oligodendrocytes(which provide suppo and insulation to axons in CNS) The term Leukoencephalopathy refers to all of the brain white matter diseases Toxic leukoencephalopathy or toxicspongiform leukoencephalopathy is a rare condition that is characterized by progressive damage (-pathy) to white matter (-leuko-) in the brain (-encephalo-), paicularly myelin, due to causes such as exposure to drug abuse, environmental toxins, or chemotherapeutic drugs