Treating the immune system can dramatically ease the suffering of people with chronic pain from an injured limb or following an amputation, a finding that could change the way such pain is treated, scientists said on Monday.

Researchers from the University of Liverpool said a dose of a blood product called intravenous immunoglobin (IVIG) significantly reduced pain in almost half of patients with Complex Regional Pain Syndrome (CPRS) - an unexplained chronic condition that can develop after injury to, or loss of, a limb.

“The discovery is expected to have a real impact on the treatment of other unexplained chronic pain conditions; if one pain condition can be effectively treated with an immune drug, then it is possible that other types will also respond,” said Andreas Goebel, an expert in pain medicine who led the study.

IVIG is a human blood antibody used to treat immune disorders and some forms of leukaemia. It balances immune systems, strengthening those that are weak and reducing activity in those that are overactive.

The researchers, whose study was published in the Annals of Internal Medicine journal, gave a single low-dose transfusion of IVIG to 13 volunteers with pain syndrome and found it significantly eased the pain in just under 50 percent of them.

The pain relief lasted five weeks on average and the treatment had few adverse side effects, they said.

“The real effect of this treatment…may turn out to be even greater than what we have already seen,” said Goebel.

He said that while the patients in the study were given a single, low-dose infusion of IVIG, the treatment could in future be given in higher doses, and repeated to give extra benefits.

The scientists said they were trying to develop ways to allow patients to administer IVIG treatment in their own homes.

According to the researchers, complex regional pain syndrome - also commonly called reflex sympathetic dystrophy - can arise after any type of injury.

Some forms follow damage to a nerve, and in some cases the pain can be so severe that patients request amputation, only to find that the pain returns in the stump.

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* Treating immune system reduced pain in half of patients

* Researchers say results may alter approach to chronic pain

* Chronic pain condition can arise from many types of injury

LONDON (Reuters)