What it is
Pre-existing conditions include any prior injury, illness, surgery, or chronic medical condition documented in the claimant's medical records before the accident date. Common examples that appear in personal injury cases: prior auto accidents with similar injuries, degenerative disc disease (nearly universal in adults over 30), prior back/neck pain treated by chiropractor or physical therapist, prior depression or anxiety, prior chronic pain conditions, and prior surgeries. Defense attorneys subpoena medical records typically going back 5-10 years (sometimes longer for serious cases) specifically to identify pre-existing conditions they can use to attack causation. The eggshell plaintiff rule (sometimes called "eggshell skull doctrine") holds that the tortfeasor takes the victim as they find them — a defendant is liable for the full extent of actual injury caused, even when the claimant's pre-existing vulnerability made them more susceptible to injury. The doctrine has two related applications: direct causation (the accident caused the injury, regardless of pre-existing vulnerability) and aggravation (the accident worsened a previously stable condition).
How it works in practice
In practice, defense attorneys use a predictable sequence in pre-existing-condition attacks. First, they subpoena ALL prior medical records — primary care, specialists, chiropractors, emergency department visits, mental health records. Second, they identify any prior complaints similar to the current injury (prior back pain, prior headaches, prior depression). Third, they retain an IME doctor who will opine that the claimant's current symptoms are caused by pre-existing degeneration or prior trauma rather than the accident. Fourth, they argue at trial that the jury should attribute most or all of the claimant's symptoms to the pre-existing condition. The claimant's response strategy: (1) full disclosure to your attorney of ALL prior medical history (concealment is fatal); (2) get the treating physician to explicitly document whether the accident caused new symptoms or aggravated previously stable ones; (3) use the eggshell plaintiff rule to argue that the defendant is liable for the FULL aggravation even when the underlying condition pre-existed; (4) demonstrate "asymptomatic baseline" — that the pre-existing condition was not causing daily-life impairment immediately before the accident.
How Pre-Existing Condition affects your settlement
Pre-existing conditions are present in almost every personal injury case — degenerative changes are nearly universal in adults — and how they're handled is the single biggest factor in settlement value for any case involving prior medical history. A claimant with a herniated disc visible on MRI who has prior chiropractic visits for "occasional back stiffness" can have her case characterized two completely different ways. Defense framing: "claimant has chronic back problems, MRI shows pre-existing degeneration, accident was minor and aggravation if any was minimal" — settlement target $10,000-$20,000. Claimant framing with proper development: "claimant had asymptomatic degenerative changes (universal in adults), accident caused acute symptomatic herniation, eggshell plaintiff rule applies, defendant liable for full aggravation including ongoing pain and need for surgical consult" — settlement target $50,000-$120,000. The 4-6x swing turns entirely on medical-causation expert testimony and documentation. Three concrete moves: (1) tell your attorney about EVERY prior medical visit, even ones you think are minor — surprises in deposition destroy credibility; (2) get the treating physician to write a "causation letter" specifically addressing whether the accident caused new symptoms, aggravated previously stable ones, or both — this letter is the cornerstone of the eggshell argument; (3) in cases with significant pre-existing history, consider retaining a medical-causation expert (often the treating physician with supplemental testimony, or a retained expert) — the additional cost typically returns 5-10x in settlement value. Pre-existing mental health conditions deserve special attention; defense attorneys frequently attribute post-accident depression or anxiety to "prior history" when the accident materially worsened the condition.
Related SetCalc guides
Related glossary terms
Informational only and not legal advice. Settlement-dollar implications described here reflect typical patterns and may differ in any specific case. Confirm the analysis for your situation with a licensed attorney.