A study by the US Mayo Clinic found eight of 19 patients who underwent blood plasma replacement, which is sometimes used to fight other illnesses, showed "moderate to marked improvement in their neurologic condition".

Participants in the study had been suffering disabling attacks from multiple sclerosis, which causes the body to attack its own central nervous system, including paralysis and speech loss. They had failed to respond to traditional anti-inflammatory steroid treatment.

Plasma exchange treatment involves removing the patient's blood and separating out the blood cells from the fluid plasma.

The blood cells are then combined with new plasma and the mixture returned to the patient.

Patients in the study underwent seven treatments over 14 days.

Exciting results

Lead researcher Dr Brian Weinshenker said: "We are very excited about the success of plasma exchange, which offers another option for multiple sclerosis patients with devastating attacks who have been unresponsive to all other forms of therapy."

Although the reason for the treatment's effectiveness was not understood, Dr Weinshenker speculated that replacing patients' plasma blunted the attack on the nervous system by antibodies contained in the original plasma.

However, four of the eight patients who responded well to the treatment experienced recurrent attacks over six months of follow-up.

While the results opened new lines of research, Dr Weinshenker cautioned that plasma exchange is not a cure for the mysterious and usually fatal disease and should not be considered as an initial treatment for attacks.

The research will be published in the December issue of the journal Annals of Neurology.