The familiar eggshell skull principle requires the defendant to take the claimant as they are. The same reasoning can apply where the vulnerability is psychological rather than physical. A greater psychiatric reaction does not become irrelevant simply because another person might have reacted differently. However, the principle does not make every later symptom attributable to the accident.
Previous Mental Health Does Not Decide the Claim.
A psychiatric history can be highly relevant without providing the answer by itself. Earlier records may show anxiety, antidepressant use, counselling, workplace stress, bereavement, or a previous depressive episode. Those entries may help explain the claimant’s baseline before the accident.
What matters is how the person was functioning before the index event. They may have been working normally, managing family responsibilities, and living independently despite an older diagnosis. In that situation, a substantial deterioration after the accident may still represent an important change. The earlier vulnerability forms part of the background rather than cancelling the later injury.
A different picture is presented when active symptoms were already affecting daily life. Ongoing treatment, medication, work absence, or recent relapse may all alter the causation analysis. The expert must then distinguish what was already present from what was added by the accident.
The Baseline Needs More Than a Diagnosis.
A reliable baseline is not created by listing old diagnoses. Function before the accident needs to be understood in practical terms. The expert may consider work, relationships, independence, treatment, medication, and recent psychological stability.
Two claimants with the same diagnosis may therefore have very different starting points. One may have been stable for years without treatment or functional difficulty. Another may have been receiving active psychiatric care immediately before the accident.
Those differences matter because causation depends on the change from the pre-accident position. Without that comparison, later symptoms can easily be over-attributed or under-attributed to the incident. A historical diagnosis should therefore be interpreted rather than simply recorded.
Vulnerability Is Not the Same as Inevitability.
A claimant may have been more susceptible to psychological injury without being destined to deteriorate. That distinction is central when causation and prognosis are considered.
Previous depression may increase vulnerability to another episode, but it does not establish when that episode would have occurred. A history of trauma may also increase susceptibility without making future psychiatric injury inevitable. The expert should therefore consider what would have happened without the accident.
Sometimes the evidence suggests that similar deterioration was already likely within a comparable period. In other cases, the person’s mental health had remained stable until the accident changed that course. The opinion should reflect the evidence rather than assumptions about psychological fragility.
The Accident May Aggravate an Existing Condition.
Not every case involves a completely new psychiatric diagnosis. An accident may aggravate an existing condition or accelerate symptoms that might otherwise have developed later.
That distinction can affect both prognosis and the extent of accident-related harm. A temporary worsening may justify a different opinion from a permanent increase in symptoms. Acceleration may also require consideration of when deterioration would have occurred without the incident.
The expert should explain these differences rather than rely on vague terms such as exacerbation. The report should identify what changed, how long the additional impact lasted, and how function was affected. This gives the opinion practical meaning and avoids treating every post-accident symptom as one undivided condition.
Medical Records Need Context.
Psychological history is often spread across primary care records, counselling notes, occupational health material, and medication histories. Those records can be valuable, but isolated entries can also be misleading.
A single antidepressant prescription may reflect a short episode rather than continuing illness. Repeated consultations may suggest a more persistent problem, while a treatment gap may have several explanations. Reduced attendance can indicate recovery, but it may also reflect reluctance to seek further help.
Contemporaneous records should therefore be considered alongside the claimant’s account and functional history. Significant differences should be addressed, but they should not automatically be interpreted as dishonesty. The report should explain whether the records support, weaken, or only partly support the claimed deterioration.
Psychological Vulnerability Should Not Become Suspicion.
Physical vulnerability is often accepted as part of ordinary medical complexity. Psychological vulnerability can sometimes attract a different and less helpful response.
A previous anxiety disorder does not make a claimant unreliable. Earlier trauma does not make later symptoms imaginary or inevitable. These histories make the assessment more complicated, but they do not answer it.
The expert should remain focused on diagnosis, causation, prognosis, and functional impact. Alternative causes should be considered without treating vulnerability as a reason for disbelief. The same discipline should be applied whether the pre-existing condition is psychiatric or physical.
The Opinion Should Explain What Changed.
The strongest reports usually compare the position before and after the accident. They identify whether symptoms were active, historic, stable, or worsening before the event. They then explain the nature and extent of any deterioration afterwards.
The accident may have caused a new condition, worsened an existing one, or accelerated an expected future decline. It may also have made little material difference where substantial symptoms were already progressing naturally.
The answer is rarely all or nothing. Psychological vulnerability does not provide a discount, but it does not remove the need for causation analysis. The claimant should be assessed according to the actual change caused by the accident.
The eggshell mind principle matters because people do not enter personal injury claims with identical psychological histories. Some will already carry anxiety, trauma, depression, or other vulnerabilities when an accident occurs. Those vulnerabilities should be understood as part of the baseline, not treated as a defect in the claim.
The task remains to identify what the accident changed and what would have happened anyway. That distinction keeps the opinion fair to both sides and grounded in the evidence.
