Progressive multifocal leukencephalopathy

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  • i. Was once relatively rare, occurring only in patients with leukemias, lymphomas and renal transplants, but now is very common in AIDS patients
  • ii. Symptoms: focal neurologic deficits including dysarthria, limb weakness, visual disturbances, ataxia, personality changes, and occasionally seizures; usually progresses over a few months resulting in progressive neurologic impairment and eventually death
  • iii. Cut surface of the fixed brain appears asymmetrically pitted by small foci of gray discoloration mixed with larger confluent areas of abnormal parenchyma
  • iv. Microscopically there are multiple foci of demyelination containing moderate numbers of foamy macrophages but only scant perivascular lymphocytes
    • 1. striking feature is the presence of very large astrocytes with bizarre, pleomorphic, hyperchromatic nuclei; but in general there is very low cellularity and there may be viral inclusions at the periphery of the foci of demyelination in enlarged nuclei of oligodendrocytes
    • 2. there is a relative preservation of axons
  • v. PML is caused by the JC virus (a papovavirus) which causes an asymptomatic infection; PML is thought to result from reactivation of latent JC virus residing in the CNS
  • vi. NOTE: leukencephalopathies (other than PML) resulting in loss of myelin, poorly cellular white matter, and diffuse gliosis may be caused by a number of conditions including leukemia, cyclosporin and FK-506 toxicity, and methotrexate use
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