Dr. Jeffrey P. Staab, a specialist in psychosomatic and behavioral medicine at the Mayo Clinic in Rochester, Minn., said it took two decades of research to come up with the new concepts, which eliminate the focus on medically unexplained symptoms. Instead, the new diagnoses put a focus on undue attention to bodily symptoms and excessive health concerns, which, when properly explained, can be very reassuring to patients.

“Health anxiety and body vigilance are much more understandable to patients when they realize they can have these things despite what their doctor finds,” he said in an online report to health professionals. “We found it much easier to engage patients if we identified what the problem was instead of what it was not.”

In patients with somatic symptom disorder, chronic symptoms result in excessive concern, fear and distress that something is seriously the matter, prompting them to seek repeated exams that rarely relieve their fears despite negative findings. In fact, negative test results can increase patients’ fears that their problems will never be correctly identified and treated.

As many as 5 percent of patients visiting doctors’ offices believe they have a serious, undiagnosed medical illness when none can be found. The persistent anxiety itself becomes a debilitating illness. Such patients are likely to insist that the medical care they received was inadequate. Even their doctors may wonder if they might have overlooked something that could explain the patient’s symptoms.

Patients with illness anxiety disorder may, or may not, have a real medical condition, but they experience exaggerated bodily sensations, like sweating or a rapid heart beat, that can result in extreme anxiety about the possibility they have a serious underlying illness. They constantly check their bodies for signs of illness and devote undue time and energy obsessively seeking an explanation for what might be wrong with them. Every cough is pneumonia, every chest pain a heart attack, every headache a possible brain cancer or incipient stroke.