ALISON WATSON v LANCASHIRE TEACHING HOSPITALS NHS FOUNDATION TRUST

A claimant must prove causation on the balance of probabilities even where breach of duty is admitted. In a medical negligence claim, diagnosis and causation must be assessed from the whole evidential picture, including the onset, progression and resolution of symptoms and the reliability of expert analysis. ABCD2 and Rosier scores are referral filters, not diagnostic tests. Evidence from studies may not be transposed uncritically from an elderly or materially different study population to a young claimant with different risk factors and a different possible mechanism of injury. Where the evidence does not establish that treatment would probably have prevented the injury, the claim fails.

The claimant suffered a serious stroke in May 2015 after attending the defendant’s hospital with visual disturbance, facial droop, speech difficulty, headache, vomiting, photophobia and subsequent left-arm weakness. The defendant admitted that the claimant should have received a differential diagnosis of TIA and referral to its TIA service, but denied that the breach caused the later stroke.

The trial concerned the side and timing of the neurological symptoms, whether the March episode was caused by multiple TIAs precipitating migraine or sporadic hemiplegic migraine, and whether prescribed Aspirin would probably have prevented or materially reduced the May stroke.

1. Outcome. The claim was dismissed and judgment entered for the defendant. The claimant was ordered to pay the defendant’s costs on the standard basis, subject to further submissions on the detailed costs order.
2. The court preferred the evidence of Dr Sare to that of Professor Brown. The pattern of symptoms was important. Visual disturbance, headache, photophobia, nausea and vomiting, followed by motor symptoms after 15–20 minutes and resolving in sequence, were more consistent with migraine with motor aura than with multiple TIAs. The diagnosis was therefore sporadic hemiplegic migraine.
3. ABCD2 and Rosier scores were held to be primary-care or emergency-department filters used to identify risk and trigger referral. They were not diagnostic tests and could not establish that the March symptoms were TIAs.
4. The court rejected the theory that the March symptoms were multiple TIAs followed by migraine. That theory required several clots in different vascular territories or a cardiac source. The evidence did not establish a probable source of multiple emboli, and the subsequent stroke did not itself make a preceding TIA probable.
5. Although Aspirin would have been prescribed if the claimant had suffered a TIA, the claimant had to prove that it would probably have prevented the May stroke. The Rothwell study concerned a substantially older, mainly male population with different vascular characteristics. Its results could not be applied without proof to a 29-year-old woman without atherosclerosis or a proved cardiac condition. The evidence did not establish that Aspirin would have reduced the relevant risk by more than 50% or prevented the stroke on the balance of probabilities.

The judgment describes a preliminary issue on causation ordered by Master Thornett on 10 July 2019. It records adjournments of the trial, including because of the COVID-19 pandemic, but does not describe any appeal or earlier judgment on the merits.