The New York Times, 25 March 2008

Lucy, one of my longtime patients, has a neurological ailment she believes I have been unable to adequately diagnose.

Although I hope to make further progress on her case, I have also told her that there may never be a definitive answer. Not surprisingly, she is feeling pretty frustrated with me.

Why do doctors and patients often approach the diagnosis of disease so differently?

Part of the answer lies in the concept of triage — the notion, originated in wartime, of caring for the sickest and most salvageable patients first. Once they were saved, attention could be turned to less drastic cases.

A similar strategy has evolved in emergency rooms, where physicians are trained to “rule in” or “rule out” severe conditions. Thus, doctors immediately consider heart attacks or pulmonary embolisms for patients with chest pain, and intestinal rupture for those with abdominal pain.

But what happens when these conditions are ruled out? In such cases, doctors proceed to search for less dire (and, it must be said, more mundane) diagnoses. The trouble is that at this stage, some physicians, busy with other patients and duties, lose interest.

For example, many patients with chest pain carry a diagnosis of costochondritis (inflammation of the chest wall bones) or gastroesophageal reflux (regurgitation of stomach acid into the esophagus).

These are real conditions. But they tend to generate little interest from many physicians, who may refer to them as “wastebasket diagnoses,” offered when nothing more serious has turned up.

The frustration of patients who believe that the medical profession takes these types of ailments too lightly has led groups of them to form alliances to publicize their illnesses. Foremost among them are fibromyalgia, a syndrome involving muscular and other pains, and chronic fatigue syndrome, which has recently been given increased credibility by the Centers for Disease Control and Prevention.

Part of the problem with these conditions is that existing treatments are not nearly as effective as those for, say, heart attacks and pneumonia. As a result, doctors may grow irritated when patients continually complain of symptoms that cannot be “cured.”

Patients’ frustration may rise even more when their conditions are especially obscure. I once had a patient who complained of persistent drenching sweats that forced her to change her bedclothes several times a night.

Upon learning of this problem, I first went into triage mode, ruling out possible dangerous causes, including tuberculosis, a thyroid abnormality and rare tumors that release hormones. I referred her to a gynecologist on the chance that she was getting hot flashes decades after her menopause.

When all the tests were negative, my patient was understandably upset, even angry. “No doctor that I have spoken to has been able to tell me what it is,” she said, as I remember. She even called a doctor on a local radio show for his opinion.

I recalled this story when I learned recently that my longtime patient Lucy’s new neurologist was questioning whether she had multiple sclerosis, a diagnosis she has carried for more than 25 years. Since I have known her, Lucy has had painful and weak legs that necessitate a walker.

Rather than simply corroborating her existing diagnosis, this doctor had thought outside the box, noting that Lucy’s relatively stable condition — and her lack of brain lesions on an M.R.I., a test not available at the time of her initial diagnosis — warranted a new perspective.

At first, Lucy was excited too. After all, being told you may not have a serious disease like multiple sclerosis is surely good news.

But while the neurologist had correctly questioned the diagnosis, she had a harder time finding a new one. Lucy became discouraged. “I want to know,” she told me. “I point-blank asked the neurologist, ‘What is it?’ And the only answer she can give me is: ‘I don’t know. I’m not sure.’ ”

Eventually, the neurology team decided that Lucy had an atypical form of multiple sclerosis, one that caused unusual neurological symptoms and was present in the spinal cord but not the brain. Yet the doctors admitted that this diagnosis generated more questions than answers about Lucy’s prognosis and her future treatment.

While trying to be as sympathetic as possible, I find myself reminding Lucy of the limits of certainty in medicine. Despite enormous advances in technology, some diagnoses may remain elusive. I also told her that it was highly unlikely her doctors missed diagnosing a disease that could have been successfully treated. But she remains convinced that she deserves to know exactly what she has.

So we will continue to search.