In most cases involving a delay in diagnosis, a major problem is that or proving causation. In all medical malpractice cases, the burden is on the claimant to prove (1) negligence and (2) what injury was caused by the negligence (this is the causation issue).

A classic example is a case in which a diagnosis of cancer is not initially made, even when there are signs and symptoms to suggest the diagnosis. The mistake leading to the delay may be that of a physician who doesn’t misses the significance of the signs and symptoms, a radiologist who misses a key finding, a pathologist who misreads the pathology slides, etc. In some cases a defendant may retrospectively acknowledge negligence, but still contend that the delay did not cause provable injury.

In cancer cases, depending on the type of cancer, causation may be provable by experts who can explain the growth or pattern of the cancer cells in order to work backward from the point of diagnosis to the point when the diagnosis should have been made. That is an easier burden to meet when it is a more common cancer where there are numerous published studies about the cancer, such as breast cancer. But for many less common cancers, there is a dearth of published studies or data that would allow that kind of analysis.

Washington recognizes “loss of a chance of a better outcome” as a cause of action. So even if it is not possible to prove that a particular bad outcome is more likely than not caused by the delay, it may be possible to prove that the chance of a better outcome was reduced.

An example is where a delay means a cancer patient went from a 45% chance of five-year recovery to a 15% chance. The problem is that the law requires that the “loss of a chance” be quantifiable, and usually that evidence can only be provided by medical experts. Many of them are loathe to speculate about “what if” questions, unless there is (as in the breast cancer example) a lot of published data on which to base an opinion.

A variation on the issue of causation arises in cases where the evidence needed to prove causation isn’t available because the defendant was negligent. A classic example is where the patient has a bad outcome from a fractured leg that wasn’t x-rayed in an emergency department. The consulting expert may not be able to say how much worse the fracture became when the patient was weight-bearing over time, because the expert can’t compare the diagnosed fracture with how it would have appeared in the missed x-ray.

That same problem occurs in cases where a diagnostic or screening test, like a mammogram or colonoscopy, was not done when it should have been, thus depriving the expert of the date needed to express an opinion on causation when the cancer is not diagnosed on a timely basis.

It is often difficult to explain this to a potential client who has had a poor outcome and thinks the negligence is clear. To be successful in a malpractice case, one has to establish the link between that bad outcome and the negligent care, i.e., that the poor outcome was caused by the negligence.

Interestingly, physicians also are confused by this issue. When physicians evaluate whether there was bad care, such as peer review of a physician’s practice, they focus on whether the bad care had the potential to cause injury to a patient, whether or not such injury actually occurred.