Ever since it was first given its name, in 1988, the condition known as chronic fatigue syndrome has been trivialized by doctors and laypeople alike, dismissed as mere malingering. So it felt momentous, earlier this month, when the Institute of Medicine released an exhaustively documented report announcing that CFS—also called, in some circles, myalgic encephalomyelitis, because of its effects on the muscles and brain—is real. As the authors put it, “The primary message of this report is that ME/CFS is a serious, chronic, complex, multisystem disease that frequently and dramatically limits the activities of affected patients.” They suggested that it be given a new name: systemic exertion intolerance disease.

The report devotes hundreds of pages to assessing the medical literature on ME/CFS, ultimately judging it an organic disease—one rooted in the body rather than in the mind—with clear physiological markers, including diminished cardiovascular function, even after exercise; slowed information processing in the brain; and orthostatic intolerance (lightheadedness, blurred vision, and other symptoms that develop when a patient stands up). People with ME/CFS, the report noted, are more “functionally impaired” than those with Type 2 diabetes, multiple sclerosis, and congestive heart failure—diseases that we know to be very grave indeed. Their rate of unemployment is estimated at between thirty-five and sixty per cent, and up to twenty-nine per cent of them will at some point be bedridden or housebound because of the illness, which frequently strikes people in their forties or fifties. “I was uninformed,” Ellen Clayton, the chair of the I.O.M. committee and a professor at the Center for Biomedical Ethics and Society, at Vanderbilt University, told me. “As I went through the literature and listened to patients, I became completely convinced.” She and her colleagues estimate that there are as many as two and a half million people living with ME/CFS in the United States, perhaps nine in ten of whom are undiagnosed.

The language that we use to talk about diseases shapes our understanding of them, as I myself found in the years in which I was mysteriously ill before being given a diagnosis. And so the I.O.M.’s proposed new name for chronic fatigue syndrome is meant to elicit broader recognition of the condition’s severity. The use of the word “fatigue,” after all, invites a misapprehension: we presume to know what it feels like, when in fact the fatigue that affects ME/CFS patients is as different from regular, end-of-the-day tiredness as Ebola is from the common cold. A patient named Jennifer Brea, who is at work on a documentary about ME/CFS, told me that her fatigue is variable: it ranges from severe flu-like feelings to an acute sense that her very cells have lost all their energy, which can make it hard to get enough air to call out for help. She traces the onset of the disease to a high fever that lasted ten days. Even with such extreme symptoms, though, Brea had trouble getting a diagnosis. “A neurologist told me, ‘All your symptoms are psychosomatic—you have a conversion disorder, caused by a distant trauma you can’t recall,’ ” she said. Clayton confirmed that experiences like Brea’s are common. “Patients told us over and over and over again how frequently they were met with skepticism, how frequently they were told by physicians that it was all in their head,” she said.

Part of the reason that the medical community has been so slow to acknowledge ME/CFS is that there is no conclusive way to test for it, and medicine today tends not to be well attuned to patient testimony. (On Friday, researchers at Columbia University’s Mailman School of Public Health announced findings that may make it easier to test for ME/CFS biomarkers in the blood.) In his book “Our Present Complaint,” the Harvard historian Charles Rosenberg argues that, ever since the nineteenth century, when cholera pandemics swept the globe and germ theory came of age, medicine has increasingly put its faith in the measurable—temperature and blood-pressure readings, X-rays, microscopy, laboratory analyses, and so forth. This way of thinking, which has usually produced excellent results, has had the unintended effect of making us skeptical of diseases whose etiologies are poorly understood—those, like ME/CFS, for which there isn’t a clear single cause. When this happens, we may blame the mind of the patient, as Brea’s neurologist did. Before we understood what multiple sclerosis was, for instance, we called it hysterical paralysis, and for decades we thought that ulcers were caused primarily by stress, when in fact bacteria are more often responsible.

Because the biology of ME/CFS remains mysterious—because it exists in a gray area that our mechanistic, muscle-through-it culture treats warily—study of the disease has languished. Last year, the National Institutes of Health allocated only about five million dollars in ME/CFS research funding—less than it did for hay fever. More than two-thirds of medical schools fail to include information about ME/CFS in their curricula, and medical textbooks, one study cited by the I.O.M. found, fare little better. This lack of information no doubt contributes to physicians’ frustration with the disease. As one Medscape commenter aptly put it, “Doctors blame patients for their inability to treat them. When we can treat this the blame will go away.” In the meantime, the brunt of that blame continues to fall on the undiagnosed. Surveys by two patient-advocacy groups, the Solve ME/CFS Initiative and ProHealth (the latter of which also markets nutritional supplements), found that up to three quarters of patients can expect to wait more than a year for a diagnosis, and nearly a third can expect to wait five years or more. Even after diagnosis, patients may be met with disbelief. This matters, because recognition from others is an important part of learning to live with an illness: it is harder to focus on getting better and to cope with a distressing new reality when you have little or no support.

The I.O.M. paper is undoubtedly an important advance, but not all ME/CFS patients are convinced that rechristening their disease will help. “It’s hard for me to understand how they came up with a name that, to me, is as bad and as stigmatizing as CFS,” a patient in San Francisco told me. (She was nevertheless impressed by the report’s rigorous summary of the medical literature.) “I asked a few friends what they thought, and the first response was, ‘Wow, that sounds like a euphemism for laziness.’ ” She underscored the need for follow through: “The key thing is, what happens next? How does this get disseminated to doctors? How does it get taught in med schools?” Brea said the same. “The big question is how this mass of information is going to be translated into useful tools. We have to remember how entrenched these ideas about ME/CFS are, and how hard it is to change them.” As she and other patients pointed out to me—and as the report stresses—there are still questions about how best to differentiate ME/CFS from other illnesses that may resemble it. (Chronic fatigue can also be a symptom of some autoimmune disorders, Lyme disease, and babesiosis, which is caused by a parasitic microorganism.) The I.O.M. report proposes a new set of diagnostic criteria, but, since they were drawn up on the basis of limited research, they will inevitably miss some people.

This is the downside of our medical culture, whose main struggle now, it seems, is to acknowledge what it doesn’t yet know while clarifying what it does. In some corners, it has become too easy to forget that a disease that isn’t understood may still be very real. As Sinclair Lewis reminded us in “Arrowsmith,” his account of the early-twentieth-century ardor for the laboratory, there is a time to be alive to scientific uncertainty. In that novel, the protagonist’s mentor, a German-accented bacteriologist named Max Gottlieb, stands beside his test tubes and his microscope and declares, “He is the only real revolutionary, the authentic scientist, because he alone knows how liddle he knows.”