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
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.