Progressive multifocal leucoencephalopathy
Progressive multifocal leucoencephalopathy is an opportunistic viral infection of the central nervous system characterized by foci of demyelination in the white matter of the cerebral hemispheres, sometimes also involving the brainstem, cerebellum, and the spinal cord (Richardson 1965; Henson and Urich 1982). Progressive multifocal leucoencephalopathy was formerly a rare disorder, usually occurring as a terminal event in patients suffering from the reticuloses and the leukaemias, and occasionally in sarcoidosis, tuberculosis, carcinomatosis, or apparently healthy individuals, but it has emerged as one of the common neurological manifestations of HIV1 infection (Berger et al. 1987).
The pathological lesions vary in size and usually consist of areas with confluent demyelination and axon preservation. Inflammatory cell infiltration is absent, but the astrocytes are characteristically enlarged, often with bizarre and mitotic nuclei.
Oligodendrocytes show pale nuclei and contain inclusion bodies. Brain imaging shows multiple low-attenuation areas. It results from opportunistic invasion of the nervous system in patients with defective immune responses by papovavirus (Zu Rhein and Chou 1965), which can be detected within affected oligodendrocytes; the agent has been characterized as one of the polyoma SV subgroup of papovaviruses, now generally called the JC type, but SV40 and BK viridae have also been implicated. The demyelination results from viral destruction of oligodendrocytes.
Progressive multifocal leucoencephalopathy is characterized by symptoms of massive destruction of cerebral or cerebellar white matter, producing convulsions, quadriplegia, aphasia, visual-field defects including blindness, dysarthria, and ataxia, leading eventually to coma and death. The cerebrospinal fluid is usually normal. Other opportunistic infections (especially cryptococcosis or listerosis) to which immunocompromised patients are also vulnerable sometimes further complicate the clinical picture. The disorder usually terminates fatally in 3–6 months from onset, but treatment with antiviral drugs is occasionally associated with prolonged survival.