New research suggests a common biomarker for inflammation is present for years in people with chronic fatigue syndrome (CFS).

People with chronic fatigue syndrome often have trouble explaining why they feel exhausted and in pain.

The condition, now generally referred to as myalgic encephalomyelitis (ME) or CFS, causes extreme and persistent tiredness. It's long been surrounded by controversy, with some doctors maintaining it's largely a psychological disorder.

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But most sufferers and an increasing number of researchers believe its roots lie in a -- so far unidentified -- biological process.

Around 250,000 people in the UK are affected but uncertain about the nature of the illness. This means there are no treatments that have been shown to work for all patients.

In extreme cases CFS leaves people bedridden and even those with moderate symptoms often have to ration their daily activity or give up work.

Viral infections, problems with the immune system, an imbalance of hormones and psychiatric problems such as trauma and stress are some of the suggested causes.

"This study delivers what has eluded us for so long: unequivocal evidence of immunological dysfunction in ME/CFS and diagnostic biomarkers for disease," said Dr. W. Ian Lipkin, director of the Center for Infection and Immunity and professor of neurology and pathology at Columbia's Mailman School.

To reach their findings, researchers analyzed the blood plasma samples of 298 CFS patients and 348 people without the disease.

The researchers found distinct biomarkers created by the immune system in those with the disease. They also found differences in those who have had the disease for less than three years and those who have had it more than three years.

Some experts urged caution and said the findings would have to be repeated in other studies before being considered a genuine breakthrough.

Before there can be effective treatments for CFS, there must be a better understanding of CFS so it can be diagnosed earlier.

TagsChronic Fatigue Syndrome, chronic fatigue, myalgic encephalomyelitis, Me, CFS, biomarker, immunological dysfunction, immune system