The mysterious disease known as chronic-fatigue syndrome has long defied classification, as the millions of people who suffer from it show a wide variety of symptoms. Now a panel commissioned by the US Department of Health and Human Services (HHS) has produced what is sure to be an influential report on how the disease should be diagnosed. This new definition comes with a new moniker: systemic exertion intolerance disease (SEID).

The report, released by the US Institute of Medicine (IOM) on February 10, says that the new name better reflects the key symptom of the disease—extreme exhaustion after any exertion. It argues that other symptoms, such as poor sleep and cognitive impairment, are secondary. But some experts are already challenging the name and revised diagnostic criteria.

Leonard Jason, a psychologist at DePaul University in Chicago, expects that patient advocacy groups will find fault with the new name, feeling that they were not adequately consulted. “As a community psychiatrist who values citizen participation in critical decisions, I think this was a strategic mistake,” he says.

In contrast, members of the IOM panel say that the new name could help patients suffering from the disease, whose existence has long been doubted and even mocked. “If I never hear another person say ’I'm chronically fatigued too,’ it won't be too soon,” says committee chair Ellen Wright Clayton, an expert on law and genetics at Vanderbilt University in Nashville, Tennessee.

Research has shown that even many physicians are sceptical about the existence of CFS, and most do not know how to diagnose it. More specific critieria should address that problem. “That will in the end get more people cared for and treated,” says Peter Rowe, a paediatrician and chronic-fatigue expert at Johns Hopkins University Children’s Center in Baltimore, Maryland, and a member of the IOM panel.

The report also attempts to simplify diagnostic criteria for the disease, addressing concerns that previous definitions were too complex. For instance, people who suffer from a mental illness can now be diagnosed with SEID. They had previously been excluded from a CFS diagnosis because the fatigue could be a symptom of depression.

Patients and researchers are universally thrilled about one aspect of the report: its definitive statement that the disease is real, not psychological. It even recommends that SEID be entered into the International Classification of Diseases (ICD-10)—the book that physicians around the world use to make diagnoses. One patient at the IOM press conference described that as “the best thing that’s happened to me” since her CFS diagnosis years ago.

Still, chronic-fatigue expert Derek Enlander, a physician in New York City, worries that the new criteria are too broad, and will result in too many patients being diagnosed. The new name, he says, is bound to confuse patients, physicians, and researchers, especially those who are not familiar with the condition.

Enlander says that the HHS, which spent US$1 million on the report, is likely to adopt the new definition. Yet the debate over the diagnostic criteria is sure to continue. “This is round one,” Jacob says.

This article is reproduced with permission and was first published on February 10, 2015.