Hidden truths

A PATIENT visits his doctor to complain of a paralysed leg. The doctor performs a battery of tests but finds nothing physically wrong with him. He considers the possibility that the cause is psychological—a so-called conversion disorder or “hysterical paralysis” that has its roots in mental or emotional trauma, and refers the patient to a psychiatrist. But there is another possibility: that the patient is faking it. With only his patient's word to go on, a doctor's chances of distinguishing a malingerer from somebody with a real psychological illness are slim. A new brain-imaging test may, however, change that.