Young v AIG Europe Ltd

In a causation dispute involving several possible medical mechanisms, a claimant may establish causation on the balance of probabilities without identifying which particular mechanism operated. The court must assess the evidence as a whole, including epidemiological evidence, medical evidence, timing and the relevant pathophysiology. A material increase in risk need not be the claimant’s only route where the evidence establishes that the injury probably would not have occurred without the defendant’s negligence. Causation remains a practical question of fact, to be determined through ordinary commonsense applied to the evidence.

The claimant suffered a myocardial infarction and spinal haematoma following a road traffic accident caused by the defendant’s insured. The defendant accepted responsibility for those injuries but disputed that the accident caused a subsequent non-haemorrhagic stroke. Four possible mechanisms were identified, including embolism associated with the myocardial infarction, arterial thrombosis and other embolic processes. The medical experts could not identify the precise mechanism. The preliminary issue was whether the accident, or post-accident treatment, caused or materially contributed to the stroke.

1. Preliminary issue. The road traffic accident caused the claimant’s stroke on the clear balance of probabilities.
2. The claimant was not required to prove which of the possible pathways caused the stroke. It was sufficient to establish that the accident probably caused the stroke, provided that conclusion was supported by the evidence as a whole.
3. The court assessed the competing medical evidence, the claimant’s background risk, the close temporal relationship between the myocardial infarction and stroke, the epidemiological evidence concerning stroke after myocardial infarction, and the additional physiological stress caused by the accident, spinal injury and surgery.
4. The epidemiological evidence could not be transferred mechanically to the claimant as an individual. It nevertheless provided important support when considered alongside the pathophysiological evidence and the opinions of the neurologists and cardiologist.
5. The evidence demonstrated more than a mere increase in risk. Although the claimant had a significant background risk of stroke, the accident and its consequences probably triggered the process leading to the stroke.
6. Causation was a practical question of fact, appropriately addressed through ordinary commonsense applied to the evidence, consistently with Alphacell v Woodward [1972] AC 824.