For 20 years, Frances Muller’s rheumatoid arthritis (RA) was misdiagnosed.

A neurologist told her that the pain in her hands was carpal tunnel syndrome. An internist told her that the all-over aches that struck about four times a year were the flu. An orthopaedic surgeon told her she had bursitis in both shoulders.

“None of my symptoms made any sense,” and none of the treatments helped, says Muller, who lives in Scottsdale, Ariz.

An orthopaedic surgeon who ordered an X-ray of her pelvis finally figured it out – after 13 previous doctors did not. He said there was no way she could have so much damage to her hips and not have RA.

Misdiagnosis is one of the most common medical errors, occurring about 15 percent of the time, according to autopsy studies. And it can have dire consequences, leading to unnecessary or delayed treatments and physical and emotional suffering.

In rheumatology, where symptoms and diseases frequently overlap, experts stress that even scrupulous, experienced and well-intentioned physicians can miss important clues, and they encourage patients to be vigilant, savvy partners in their own care.

“For many rheumatic diseases, there’s no gold standard [for diagnosis],” says Don L. Goldenberg, MD, chief of rheumatology at Newton-Wellesley Hospital in Massachusetts. “You don’t biopsy it. There aren’t a lot of laboratory tests. That’s where the art of medicine comes in, more than the science.

“If patients are concerned, they have the right [to], and certainly should, get a second opinion,” Dr. Goldenberg adds.

To help you decide when it’s time to push for more answers or to seek a second opinion, here are seven red flags that your doctor may have arrived at the wrong conclusion about your condition.