WASHINGTON (AFP) - Chronic fatigue syndrome is a disease with distinct stages that can be identified through biomarkers in the blood, researchers said Friday, offering hope that earlier diagnosis may improve treatment.
Scientists at Columbia University's Mailman School of Public Health said their findings represent "the first robust physical evidence" that the syndrome is "a biological illness as opposed to a psychological disorder, and the first evidence that the disease has distinct stages."
The report was published in the journal Science Advances.
With no known cause or cure, chronic fatigue syndrome - known formally as encephalomyelitis (ME/CFS) - has long puzzled the medical community. It can cause extreme tiredness, headaches, difficulty concentrating and muscle pain.
"We now have evidence confirming what millions of people with this disease already know, that ME/CFS isn't psychological," said lead author Mady Hornig, associate professor of epidemiology at Columbia's Mailman School.
"Our results should accelerate the process of establishing the diagnosis after individuals first fall ill, as well as discovery of new treatment strategies focusing on these early blood markers."
Researchers tested levels of 51 immune biomarkers in blood plasma samples from 298 patients and 348 healthy controls.
Specific patterns appeared in patients who had the disease three years or less.
These patterns were not visible in healthy controls or patients who had the disease for more than three years.
Those who had been sick for less than three years had higher levels of immune molecules called cytokines.
"The association was unusually strong with a cytokine called interferon gamma that has been linked to the fatigue that follows many viral infections, including Epstein-Barr virus," said the study.
However, cytokine levels did not explain symptom severity, which often fluctuates. Patients may have good days and bad days.
"It appears that ME/CFS patients are flush with cytokines until around the three-year mark, at which point the immune system shows evidence of exhaustion and cytokine levels drop," said Hornig.
Researchers said the findings support the theory that the disease may strike when vulnerable patients fall ill with a common virus like Epstein-Barr, which causes mononucleosis, and they are unable to recover.
"The immune response becomes like a car stuck in high gear," the university said in a statement.
Previous research has ruled out two viruses thought to be causing ME/CFS, including xenotropic murine leukaemia virus and murine retrovirus-like sequences.
"This study delivers what has eluded us for so long: unequivocal evidence of immunological dysfunction in ME/CFS and diagnostic biomarkers for disease," said senior author W. Ian Lipkin, professor of epidemiology at Columbia's Mailman School.
"The question we are trying to address in a parallel microbiome project is what triggers this dysfunction."