Zebra?

 To quote from Wikipedia: 

Ockham's razor (also written as Occam's razor and in Latin lex parsimoniae) is a principle of parsimony, economy, or succinctness used in problem-solving devised by William of Ockham (c. 1287 - 1347). It states that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.

While a medical zebra is:

Zebra is the medical slang for arriving at an exotic medical diagnosis when a more commonplace explanation is more likely. It is shorthand for the aphorism coined in the late 1940s by Dr. Theodore Woodward, professor at the University of Maryland School of Medicine, who instructed his medical interns: "When you hear hoofbeats, think of horses not zebras". Since horses are common in Maryland while zebras are relatively rare, logically one could confidently guess that an animal making hoofbeats is probably a horse. By 1960, the aphorism was widely known in medical circles.

Ultimately a zebra is medical condition that is an exception to Ockham's razor. 

As someone who has been diagnosed with a rare medical condition that was misdiagnosed for almost 25 years by countless doctors I consider myself to be a 'zebra'. The 'limping' aspect should be self explanatory.