WASHINGTON, Oct. 18 (Reuters) — Many veterans of combat in Iraq and Afghanistan are clearly suffering from post-traumatic stress disorder, but it is not at all clear which treatments work to help them, an expert panel from the Institute of Medicine reported Thursday. The only treatment that has been shown to work, the panel said, is exposure therapy, a gradual, step-by-step process in which patients are asked to confront memories of a trauma by recounting it in detail. Veterans Affairs hospitals now use that treatment. “At this time, we can make no judgment about the effectiveness of most psychotherapies or...