Archive

Progressive Multifocal Leukoencephalopathy (PML).

As featured in this week's Risk Factor, PML is a serious viral infection of the brain that affects those with weak immune systems, writes Graham Hopkins. "Encephalo" means "brain", and "pathy" means "disease". Encephalopathy is a disease of the brain. "Leuko" means "white". Leukoencephalopathy is a disease of the white matter in the brain. "Progressive" means it becomes worse in a short time, and "multifocal" means that it shows up in several places at the same time. PML is a disorder of the nervous system that mainly affects people with suppressed immune systems. Suppression is where the system fails to work. It can be caused by a virus attacking the system or by treatments that reduce its effectiveness such as the drugs given to transplant patients. It has been estimated that it affects from 4 to 10 per cent of people with Aids, now known as advanced or late stage HIV status. HIV, short for human immunodeficiency virus, attacks the body's immune system, making it hard to fight off diseases.

PML is caused by the "JC" virus. It attacks the myelin sheath that covers nerve cells. The myelin sheath is the fatty covering, which acts as an insulator, on nerve fibres in the brain.

People who contract PML can suffer mental deterioration, vision loss, difficulties in thinking and speaking, an inability to co-ordinate movements, paralysis and, ultimately, coma and death.

There is no cure for PML, nor is there an effective treatment. It acts quickly with death usually occurring between one and four months after it has been contracted although there are reported cases of survivors lasting for years.

For further information visit the National Institute of Neurological Disorders and Stroke website: www.ninds.nih.gov/index or Terrence Higgins Trust: www.tht.org.uk