Accurate diagnosis is the cornerstone of medical care. To plan a successful treatment for a patient, a doctor must first determine the nature of the illness. In most branches of medicine, physicians can base their diagnoses on objective tests: a doctor can examine x-rays to see if a bone is broken, for example, or extract tissue samples to search for cancer cells. But for some common and serious psychiatric disorders, diagnoses are still based entirely on the patient's own report of symptoms and the doctor's observations of the patient's behavior. The human brain is so enormously complex that medical researchers have not yet been able to devise definitive tests to diagnose illnesses such as schizophrenia, autism, bipolar disorder or major depression.
Because psychiatrists must employ subjective evaluations, they face the challenge of reliability: how to ensure that two different doctors arrive at the same diagnosis for the same patient. To address this concern, the American Psychiatric Association in 1980 published the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (widely known by the acronym "DSM-III"). Unlike earlier editions of the manual, DSM-III and its successor volumes (the latest one is referred to as DSM-IV-TR) describe what symptoms must be present--and for how long--to make a diagnosis of a particular brain disorder. Virtually all these criteria, however, are based on the patient's history and the clinical encounter. Without the ability to apply objective tests, physicians may fail to detect disorders and sometimes mistake the symptoms of one illness for another's. Making the task more difficult is the fact that some psychiatric illnesses, such as schizophrenia, may turn out to be clusters of diseases that have similar symptoms but require different treatments.
This article was originally published with the title Diagnosing Disorders.