Did you ever notice that your doctor talks more about conditions you do not have than what you do?
Likewise, if your doctor tells you that you have a particular condition, you may wonder how he or she knows. Sometimes the answer is that it doesn't seem to be anything else.
Understanding what your doctor is saying often means understanding the uncertainty of medicine — what is known is enormous, but there is still much that is unknown.
The Process of Elimination
As an example, if you see your health care professional because you have headaches, he or she might mention a list of things that are unlikely to cause them: a brain tumor, meningitis, and so on. The more serious causes may be mentioned first if those are clearly the things you (or your health care professional) are most worried about. Tests may or may not be necessary to exclude, or rule out, those possibilities but by the end of your visit, you may have spent most of the time talking about things you did not have — you even may have left the office before realizing you never really got back to talking about what is causing the headaches.
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The Diagnosis of Exclusion
An under-appreciated but undeniable truth in medical practice is that frequently health care professionals can more reliably tell what the problem is not than what it is. Sometimes this is because our understanding is limited and the condition is simply a collection of symptoms (often called syndromes ). In other conditions, the cause is unknown or there is no reliable test available to identify its presence.
Consider the headache example again: At the end of your visit, your doctor may suspect that you have tension headaches. However, there is no accurate or specific test to prove it. Ruling out other possibilities (by using your description of symptoms and other medical history, physical examination, and sometimes testing), is an important way — if not the only way — to determine a diagnosis of exclusion. Part of the process is how your symptoms respond to treatment or change over time, so a follow-up visit is usually part of the plan.
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Common Diagnoses of Exclusion
The diagnosis of exclusion is common in everyday medical practice. From persons with sore throats (told they have a viral infection) to persons with chest pain (who are reassured that they do not have heart disease), evaluation is targeted at excluding important conditions with specific therapies as much as at establishing a diagnosis. Examples of this abound, including:
- Fibromyalgia — People with this condition have pain in the joints and muscles that may seem like a form of arthritis, yet the joints and muscles are normal (by examination and testing). Making sure there is no arthritic, hormonal or other medical disorder is an important part of establishing the diagnosis.
- Irritable bowel syndrome — The abdominal pain, bloating, cramping, diarrhea and constipation typical of this disorder may suggest colitis or other intestinal disease. Some degree of testing to exclude these other disorders is usually required before the diagnosis of irritable bowel syndrome is assigned.
- Back pain — Many people with back pain are concerned about a disc or a severe form of arthritis, but in 80% to 90% of cases, no specific diagnosis can be made. A serious cause (such as a tumor or infection) is present in less than 1% of cases. Despite extensive testing, the diagnosis often remains uncertain, so physicians are trained to identify accurately the serious causes and focus on treatment (rather than diagnosis) for the rest. "Back strain" or "muscle spasm" are common diagnoses of exclusion.
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The Bottom Line
Over time, research may provide enough answers about poorly understood conditions that the diagnosis of exclusion becomes a thing of the past. In the meantime, the hardest thing for you and your doctor may be deciding when to stop ruling out unlikely possibilities and to accept the diagnosis of exclusion.
For many symptoms and illnesses, the best we can do is to make the most of our incomplete understanding. A diagnosis of exclusion may be less definitive than a diagnosis that can be proven, but reassurance about conditions you do not have may be the most helpful thing, or the only thing, your doctor can do for you.
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Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.