A pain specialist says he is perplexed by an investigation by the Repatriation Medical Authority into a chronic pain condition that has been linked to war-time service for decades.

Complex regional pain syndrome (CRPS) is debilitating, and the authority is looking at the extent to which it is caused by war or defence-related injury.

The investigation is being carried out in relation to the Veterans Entitlements Act and those eligible to make claims for veterans pensions or military compensation are being urged to make written submissions.

Marc Russo is the director of the Hunter Pain Clinic in Newcastle and has treated more than 600 people with CRPS, many of them soldiers.

He said soldiers have reported suffering from complex regional pain syndrome for decades, often caused by shrapnel and ballistic injuries.

Dr Russo said its link to war was well-known.

"I'm intrigued by their review of it," he said.

"This condition was first brought to the attention of medical professionals by a battlefield surgeon, Silas Weir Mitchell.

"He described the condition under the then term 'causalgia' and his classical description of injuries suffered by survivors of shrapnel and other ballistic injuries."

Dr Marc Russo says war-time links to the chronic pain syndrome known as CRPS are well known. ( Hunter Pain Clinic )

Expensive treatment for devastating condition

Treatment to block pain signals for suffers of CRPS can cost tens of thousands of dollars.

Dr Russo said it was a devastating condition.

"It's not really anything that you would wish on your enemy," he said.

"It is a rare condition, but a condition of unrelenting nerve pain with some associated features that go with it."

He said soldiers suffering from a CRPS often respond better to treatment than others in his care.

"I have a number of patients from a military background with the condition," he said.

"They are often very motivated individuals and tend to do a little bit better than the average person, but it is quite variable."

The Repatriation Medical Authority will hold its first meeting as part of the investigation into CRPS on June 7, 2016.