This graphic illustrates the abnormal wiring in the right hemisphere of people with complex regional pain syndrome. The colours indicate areas of damage. (Courtesy: Northwestern University)

The brains of people with a chronic pain condition look like an inept cable worker rewired areas related to emotion, pain perception and skin temperature, a brain imaging study suggests.

In Wednesday's issue of the journal Neuron, researchers reported using magnetic resonance imaging (MRI) to look for the differences in the brains of 22 normal subjects and 22 subjects with a chronic pain condition called complex region pain syndrome.

The brains of chronic pain patients showed changes in the brain's white matter, the cable-like network of fibres that deliver messages between neurons.

"This is the first evidence of brain abnormality in these patients," said the study's lead investigator, Vania Apkarian, a professor of physiology at Northwestern University's Feinberg School of Medicine in Chicago.

"People didn't believe these patients. This is the first proof that there is a biological underpinning for the condition."

The syndrome often begins with significant damage to a hand or foot. In five per cent of patients, the pain continues to rage long after the injury has healed. The cause is unknown.

Typical features include:

• Pain that radiates from the injury site, such as the hand, to the rest of the arm or even the whole body.
• Skin colour changing to blue or red, and skin temperatures that feel hotter at first and then colder as the condition becomes chronic.
• A hike in immune markers in the blood showing the immune system has shifted into overdrive.

The white matter changes are related to the duration and intensity of pain and anxiety that patients feel, Apkarian said.

Dramatic improvements or remission are possible if treatment such as anti-inflammatories, physical therapy, sympathetic nerve blockers, electrical impulses applied to nerve endings, biofeedback and spinal cord simulation are used early, according to the Mayo Clinic.

The new anatomical findings could provide targets for potential drug treatments, the researchers said.

Aside from the white matter changes, the brains of people with CRPS also showed an atrophy of the neurons or grey matter that has been found in other types of chronic pain.