Actor Christina Applegate was diagnosed with multiple sclerosis (MS) over five years ago — but this week, she announced that a recent reevaluation found that she doesn't have the condition after all. In the wake of that revelation, she's been left without a diagnosis, and she said on a podcast that she felt she was "back at square one, where I don't know what's going on with me."Applegate's case is not totally unique, although MS diagnosis has improved over the years. Studies offer different estimates of how frequently MS is misdiagnosed, with rates ranging from 5% to over 40%, depending on the patient population and clinical setting. There is also some degree of underdiagnosis — cases in wh...