Progressive multifocal leukoencephalopathy (PML)

PML was once a rare disease associated with a compromised immune system. In 1979, the rate of diagnosis of PML in the United States was 1.5 per 10 million population (about 35 - 40 cases per year). It has now become very common in AIDS patients and appears to be increasing. In the decade from 1981-1990, the rate was 0.72% of AIDS patients but by 2000, the rate had risen to about 5% of AIDS patients developing PML. At least 85% of PML cases in the United States are AIDS-associated

The symptoms of PML include:

• muscle weakness (often unilateral)
• speech problems
• cognitive problems, confusion, disorientation
• gait problems (loss of balance)
• visual problems (double or blurred vision, loss of vision in one eye)
• headaches
• sensory loss
• seizures

As might be expected, these result from brain lesions

PML is caused by a polyoma virus known as JC (the initials of the patient from whom it was isolated). Almost everyone (at least 70% of the population) has been exposed to the virus as judged by the presence of antibodies. The virus is found in kidney, lymphoid tissue and bone marrow; usually infection is without symptoms. PML often results from a reactivation of an earlier infection in a patient with a suppressed immune system. The reactivated virus is carried to the brain by infected lymphocytes. In the brain, oligodendorcytes become infected and the myelin sheath around the nerves is lost, producing visible lesions. The condition is progressive and fatal and without chemotherapeutic intervention, survival for a few months after diagnosis was common. The survival time depends on the level of CD4 cells in the patient and seems highest in patients in which PML is the first AIDS-defining event.

The introduction of HAART has increased survival times; usually survival is now a few years with about 30% of patients dying within two years of PML diagnosis.