A pre-existing condition injury claim Arizona case turns on one question: did the accident make an existing problem worse? Arizona law doesn’t punish you for having a prior injury. Instead, it protects you through what courts call the eggshell plaintiff rule, and understanding that rule changes how you should approach the whole claim.
The eggshell plaintiff rule in Arizona
Arizona courts follow the eggshell plaintiff doctrine: a negligent driver takes the victim as they find them. If your prior back condition made you more vulnerable to injury than an average person, the at-fault driver remains fully liable for the harm that vulnerability produced. The Arizona Court of Appeals confirmed this approach in Gasiorowski v. Hose, 182 Ariz. 376 (Ct. App. 1994), which held that a jury instruction on this exact point should have been given.
In practice, this means a defendant can’t argue your damages should shrink just because a healthier person would have walked away with less injury. The law asks what actually happened to you, not what would have happened to someone else.
What the rule doesn’t cover
Not X — Y: the eggshell rule doesn’t make the at-fault driver responsible for your underlying condition itself. It only covers the aggravation, the worsening, that the accident actually caused. If your back pain was already progressing before the crash, you can recover for how much worse it got, not for the condition’s natural, pre-accident trajectory.
That distinction matters because it shapes what your case needs to prove. You’re not proving the accident caused your condition. You’re proving it made an existing condition measurably worse.
How to actually prove aggravation
Comparison is everything here. Your case needs medical records from before the accident, showing your baseline condition, alongside records from after, showing the change. A treating doctor who can speak to that comparison directly carries real weight.
Disclose your full medical history early and completely. Hiding a prior injury almost never works, since insurers routinely obtain records going back years, and a hidden condition discovered later damages your credibility far more than an honestly disclosed one ever would.
An independent medical exam often plays a role here too, since the insurer’s own doctor will likely focus specifically on separating your pre-existing baseline from the accident’s actual effect.
The bottom line
A pre-existing condition doesn’t weaken your Arizona injury claim the way most people assume. It shifts the question from whether you were hurt to how much worse the accident made things. Full disclosure and clear before-and-after medical documentation turn that shift into your strongest evidence, not your biggest liability.
Frequently asked questions
Yes. Arizona's eggshell plaintiff rule holds the at-fault driver responsible for the full extent of harm, including the aggravation of a pre-existing condition.
No. It only covers the worsening the accident actually caused, not the condition's natural progression before the crash.
Yes. Full, early disclosure protects your credibility, since insurers routinely obtain years of medical history anyway.
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This article is for general informational purposes only and doesn’t constitute legal advice. How a pre-existing condition affects any specific claim depends heavily on individual medical facts.