A preexisting condition can affect several different trial questions, and an instruction about unusual susceptibility or aggravation does not decide negligence, medical causation, or the amount of damages by itself.

The record should identify the exact condition, the person’s pre-event baseline, the alleged injury mechanism, what changed, the duration of the change, alternative explanations, and which issue a requested instruction is meant to address.

Keep four questions separate

  • Liability: whether a defendant breached a duty and caused the event
  • General causation: whether the event was capable of producing the claimed type of harm
  • Specific causation: whether and to what extent this event caused this person’s claimed change
  • Damages: which losses were caused by the event and how they can be measured without assigning unrelated loss to the defendant

An unusually susceptible person is not required to have the same medical response as an average person. At the same time, the existence of a diagnosis before the event does not establish that every later symptom, treatment, restriction, or expense was caused by the event.

Hughes v. Webster illustrates why the evidence and instruction must match

In Hughes v. Webster, the North Carolina Court of Appeals examined jury instructions concerning peculiar susceptibility and aggravation in a personal-injury action. The decision illustrates that activation of a dormant condition, unusually extensive harm, and aggravation of an existing condition are related concepts but should not be treated as interchangeable labels.

A requested instruction should identify the evidentiary theory it addresses and the evidence supporting it. The court must consider the full charge and record; the presence of a preexisting condition alone does not require every possible instruction or establish a result.

Build the medical foundation for the disputed change

North Carolina Rule of Evidence 702 requires expert testimony to rest on sufficient facts or data and reliable methods applied reliably to the facts. When medical causation is outside ordinary knowledge, an opinion should identify the records reviewed, baseline assumed, event facts, reasoning, alternative causes, limits, and uncertainty.

  • Pre-event diagnoses, symptoms, treatment, imaging, medications, restrictions, function, work, and planned care
  • Event mechanism, acute complaints, examination, testing, treatment, instructions, and first documented functional change
  • Post-event chronology, response to treatment, gaps, recurrence, later incidents, intervening conditions, and differing medical assessments
  • Provider opinions separated by the question addressed: diagnosis, cause, aggravation, duration, restriction, future care, or allocation
  • Lay observations, work records, calendars, messages, photographs, and activity evidence tied to dates and specific functions

Allocation may be possible, uncertain, or unsupported

A record may support a new injury, activation of a dormant condition, worsening of an active condition, unusually extensive harm, natural progression, an unrelated later cause, or several contributors affecting different periods. Do not force one label across every symptom or time period. If a qualified witness can allocate part of a condition, preserve the basis and limits of that allocation; if not, state the uncertainty rather than inventing a percentage.

Past medical expenses have a separate evidentiary rule

North Carolina Rule of Evidence 414 addresses proof of past medical expenses. Expense proof does not by itself establish that the event caused the treatment. Separate pre-event care, post-event services, amounts paid or required to be paid, and the medical-causation evidence for the claimed services.

Use the related guide for record preparation

The related guide to documenting a preexisting condition before and after a North Carolina collision covers baseline records, chronology, functional change, authorizations, and insurer requests. This article owns the narrower task of matching evidence to a damages-instruction issue.

Rosensteel Fleishman Car Accident & Injury Lawyers provides general information about discussing a North Carolina personal-injury claim involving a preexisting condition. Liability, instruction requests, expert evidence, causation, damages, defenses, and deadlines depend on the claim and current law.

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