It has been described variously as a chronic disease, a psychiatric disorder and a figment of the imagination but now research has finally succeeded in identifying biomarkers that confirm and quantify the existence of chronic fatigue syndrome (CFS).

CFS, or myalgic encephalomyelitis, is characterised by persistent fatigue over a long period, which significantly impacts quality of life. The fatigue is unrelated to levels of physical activity. Medication and therapy have little effect.

What causes CFS is still unknown. In many cases symptoms begin suddenly, typically after a short flu-like illness. In others the onset is gradual, over a period of weeks or months. Three-quarters of sufferers are women.

The lack of defined causal agents has often made an already unpleasant situation even worse for sufferers, with some doctors, employers and insurers refusing to believe CFS is anything more than an imagined disease.

The absence of unequivocal physical criteria also means the condition can be over-diagnosed. A study led by Natalia Palacios of the University of Massachusetts found that 80% of people diagnosed with CFS did not have the necessary symptoms described on the checklist drawn up by the US Centers for Disease Control and Prevention.

Now researchers at Stanford University in California have identified 17 proteins involved in immune system signalling that signify the presence of the condition. The concentration of the proteins, or cytokines, in the bloodstream correlate exactly with the severity of symptoms.

In a paper published in the Proceedings of the National Academy of Sciences, the scientists say the presence of elevated levels of the proteins show inflammation is a key driver for CFS.

Having definite and quantifiable markers for the condition will go a long way towards CFS being recognised as a bona fide illness, despite the continuing mystery surrounding its cause. “I have seen the horrors of this disease, multiplied by hundreds of patients,” says lead researcher Jose Montoya. “It has been observed and talked about for 35 years now, sometimes with the onus of being described as a psychological condition. But chronic fatigue syndrome is by no means a figment of the imagination. This is real.”

Apart from tiredness, CFS symptoms differ substantially from person to person, ranging from mental impairment to digestive problems to muscle pain. This variety often confounds diagnosis, and in the past has added to suggestions myalgic encephalomyelitis is at best a misidentification of other disorders rather than a disease in its own right.

Montoya’s colleague Mark Davis says the identification of the proteins means a proper test that records inflammation levels rather than external symptoms may soon be possible.

“There has been a great deal of controversy and confusion surrounding ME/CFS – even whether it is an actual disease,” he says. “Our findings show clearly that it’s an inflammatory disease and provide a solid basis for a diagnostic blood test.”