Leukoencephalopathy

Leukoencephalopathy is the destruction of the myelin sheaths that cover nerve fibers. These sheaths, composed of lipoprotein layers, promote the transmission of a neural impulse along an axon. In cancer patients, especially leukemia patients, leukoencephalopathy is a rare side effect, caused by methotrexate and/or radiation. The symptoms of leukoenceopalopathy include seizures, mental dysfunction, and ataxia.

Leukoencephalopathy, also called multifocal demyelinating disease, is not at all unique to patients treated with chemotherapy and radiation. Online, most discussions of this condition are found on AIDS web sites. It can also be caused by "local injury, ischemia, toxic agents, or metabolic disorders" (Merck manual). Multiple Sclerosis (MS) is a demyelinating disease.

According to the Merck Manual, the demyelinating process can be reversed.

Progressive Multifocal Leukoencephalopathy, or PML, is a progressive disease caused by a slow virus in immune-compromised patients. Here is a description of PML:

Merck Manual

The following paragraph is directly from the Royal Belgian Radiological Society web site:

"PML is an uncommon demyelinating disease that occurs in immuno-compromised patients (lymphoma, leukemia, carcinomatosis, AIDS). The incidence of PML in adult AIDS-patients has been estimated to be up to 4%. PML is caused by central nervous system infection by group B Human Papovaviruses (Jacob-Creutzfeldt virus, simian virus 40), destroying principally oligodendroglia, thus resulting in extensive demyelination. The clinical manifestations are those of multiple, progressively enlarging lesions of the cerebral and cerebellar fiber systems: motor system abnormalities, visual loss, dementia and ultimately death, occur four to six months after onset."