There is, of course, a working definition of disease, one that most of us share: a disease is a kind of suffering caused by something gone wrong in the body. Cancer, diabetes, tuberculosis—we label these diseases not simply because they inflict pain upon us, or impair the quality of our lives, but because doctors can specify their biochemistry—the neoplasms, the lack of insulin, the bacilli that can that can confirm the presence of the disease, that can be spotted and measured and, sometimes, eradicated.

A disease may be what the medical profession recognizes as such, but doctors are reluctant admit into their realm problems without some biochemical signature. Borderline cases—chronic fatigue syndrome, major depression, restless-legs syndrome—are vexing precisely because they lack those indicators. Doctors often leave conditions like these outside the pantheon of diseases, at least until they can demonstrate their biochemical cred. Which is why you shouldn’t be surprised to read sometime in the near future about a doctor who has inserted binge eaters into M.R.I. machines and proved that the disorder is a real disease.

The lack of this kind of proof that alcoholism is a disease is what led Jellinek to wrestle with the concept. It is also why the A.P.A. has to begin its Diagnostic and Statistical Manual of Mental Disorders with a loose and baggy four-paragraph definition of mental disorder that is no more satisfying than Jellinek’s was. Without biochemistry on their side, the authors of the manual have struggled to prove that the conditions they treat belong in the realm of physicians, and their efforts have done little to reduce suspicions that the profession is too eager to turn all our troubles into their disorders.

But psychiatrists are beginning to rethink this strategy. They are going on the offensive, claiming that psychiatry’s diagnostic uncertainty (and lack of biochemical findings) is pervasive in all of medicine. They point to the many physical illnesses—Alzheimer’s disease, peripheral neuropathy, even poison ivy rashes—diagnosed without resort to biological lab tests, and to the numerous diagnostic thresholds—such as glucose levels in diabetes and blood pressure in hypertension—that have been reworked over the years. So, they argue, it isn’t just psychiatry that fails to measure up to modern medicine. It’s also much of modern medicine.

via Do disease definitions come from science or say-so? : The New Yorker.