“Of course,” I said, “if this were a boards exam question—thirty-five-year-old with unexplained weight loss and new-onset back pain—the obvious answer would be (C) cancer.”

“I think we should get X-rays first,” she said. MRIs for back pain are expensive, and unnecessary imaging had lately become a major national point of cost-saving emphasis. But the value of a scan also depends on what you are looking for: X-rays are largely useless for cancer. Still, for many docs, ordering an MRI at this early stage is apostasy. She continued: “X-rays aren’t perfectly sensitive, but it makes sense to start there.”

“How about we get flexion-extension X-rays, then— maybe the more realistic diagnosis here is isthmic spondylolisthesis?”

From the reflection in the wall mirror, I could see her googling it.

“It’s a pars fracture affecting up to five percent of people and a frequent cause of back pain in the young.”

“Okay, I’ll order them, then.”
 “Thanks,” I said.
 Why was I so authoritative in a surgeon’s coat but so meek in a patient's gown? The truth was, I knew more about back pain than she did—half of my training as a neurosurgeon had involved disorders of the spine. But maybe a spondy was more likely. It did affect a significant percent of young adults—and cancer in the spine in your thirties? The odds of that couldn’t be more than one in ten thousand.