Lost cause

In the latest edition of the JSB guidelines, the introductory note to the section on chronic pain stresses that 'questions of causation inevitably arise in such cases'. The law of causation in tort is a complex patchwork quilt of varying tests and judicial policies, and recent cases involving chronic pain have demonstrated that causation is a particularly fraught issue. As a result, expert medical witnesses play a very important role in cases where a claim for chronic pain is made. Solicitors instructing experts need to have a solid understanding of the law of causation and the difficulties it may present in this difficult area of personal injury practise.

What is chronic pain?

Pain is the body's way of telling us that we have a problem. When an injury is suffered, neurons that can sense damage (nociceptors) send a signal through the nervous system, up the spinal chord and into the brain, where we experience the signal as an unpleasant sensation. As the injury heals some pain continues, but when the healing process is over the pain subsides.

Chronic pain syndrome is the exception to this natural cycle. The people who suffer it experience pain long after their injuries have healed. When they seek a medical explanation, the doctors are unable to find an organic cause for the pain, or find that the pain is out of all proportion to its organic cause. In 1986, the International Association for the Study of Pain defined chronic pain as 'pain without apparent biological value that has persisted beyond normal tissue healing time'. Yet there is limited scientific understanding of why this condition occurs, and in individual cases the pathological events which caused the nociceptors to misfunction cannot be identified. There also appears to be a relationship '“ not yet understood '“ between psychological conditions such as depression and propensity to suffer chronic pain.

The but-for test

The law requires a causal connection between a tort and any injury in order for the tortfeasor to be liable to compensate the injured party. How a causal connection must be proven is something which may not be the same in all types of case. Nevertheless, the starting position is usually the well-known 'but-for' test. This test gives a claimant the burden of proving that their chronic pain would not have materialised if the defendant's tort had not occurred. The scientific uncertainty regarding how chronic pain develops clearly makes this a very difficult hurdle for claimants. It is also important to recognise that the but-for test is not always sufficient to establish liability. A defendant may be able to argue that there was some event subsequent to their tort (a 'novus actus interveniens') which was the effective cause of the chronic pain.

The recent case of Thorp v Sharp [2007] EWCA Civ 1433 illustrates the difficulties claimants face in surmounting the but-for test for chronic pain. The claimant had hurt her hip by tripping over some post bags in her office. X-rays showed no damage, but the claimant alleged that she had developed chronic pain as a result, amounting to a permanent disability. Although the employer had admitted liability for the accident, a judge in the Norwich County Court rejected her claim for damages in respect of chronic pain. Although he accepted that the pain's origin coincided with the accident, he would not infer causation because he could not discount that 'some unknown cause for which the defendant may not be responsible' was the effective cause. The claimant appealed, submitting that the judge had misapplied the orthopaedic evidence that there was 'no physical cause' for the continuing pain. The Court of Appeal, dismissing the appeal, acknowledged that the judge would have been wrong if he had reasoned that because there was no physical cause for the pain now, the accident could not have been a cause of the claimant's condition. However, the appellate court was satisfied that the first judge had made a legitimate finding that the causal link was simply not proven on the balance of probabilities.

Ms Thorp's case is not fatal for all chronic pain claimants: Lord Justice May's speech makes it plain that an inference in favour of a causal link to the chronic pain was available to the judge, but that circumstances pointed away from it; in particular the 'low velocity' of the accident which can only have damaged the soft tissue, and the suggestions that there were pre-existing injuries and periods where Ms Thorp was not experiencing pain subsequent to her accident.

In cases where claimants were plainly healthy and the pain followed immediately and continually from an injury, the courts will be more likely to make an inferential leap towards finding a causal link to chronic pain. For instance, in Mubarak v NSK Bearings Ltd (2007) (unreported) a judge in the Manchester County Court preferred the evidence of the claimant's pain management consultant that a forklift truck accident had caused the defendant chronic back pain, rather than the degenerative changes that the defendant's expert identified as the probable cause.

The stretching of causation

As if the complexity of the picture using the standard but-for test was not enough, it is important to recognise that the exceptions to this rule may be applied in chronic pain cases. Bonnington Castings v Wardlaw [1956] AC 613 relaxed the but-for test to the degree that it is no longer necessary to prove that without the defendant's tort the injury would not have occurred, because liability can be established if the defendant's tort merely contributed (in a more than minimal fashion) to the extent of the injury. This 'material contribution' test can be applied when there are multiple types of injury, and it is surprising that there is no reference to this test in the Court of Appeal's deliberations in Thorp.

The other test, the 'material increase in risk' test, which was established by the House of Lords in McGhee v National Coal Board [1973] 1 WLR 1 and confirmed for mesothelioma cases in Fairchild v Glenhaven [2002] UKHL 22, may assist claimants even further as it only requires them to prove that the tort increased the risk of them developing chronic pain.

Clearly, either test would assist a claimant if they were applied. The lack of scientific understanding of chronic pain's aetiology may make such assistance more likely: the current authorities suggest that the material increase in risk test applies where the state of scientific understanding is such that expert evidence cannot positively say whether the tort did, or did not, cause the injury.

On the other hand, however, defendants are assisted by the authority of Wilsher v Essex Area Health Authority [1988] AC 1074 where the House of Lords held that the material increase in risk test only applies in scenarios where there is only one type of candidate for the role of causative agent. Exactly how widely the categories of agent are construed is not altogether clear, but plainly many chronic pain cases like Thorp involve different types of potential causal agent.

There will, however, be some exceptional cases where the material increase in risk test would apply. In Pearce v Lindfield [2003] EWCA Civ 647, the extremely unfortunate claimant was the innocent victim of three near-identical car accidents, each time suffering whiplash injuries after a car drove into her vehicle while she was stationary and indicating a right turn. The trial judge held that each of the defendants was liable for the chronic pain condition that resulted, but the first and second defendants submitted, on appeal, that only the third driver could be shown, on the balance of probabilities, to have caused the chronic pain. In dismissing the appeal, Lord Justice Clarke referred to the material increase in risk test in McGhee as applying to these facts.

Case management strategies

Because there is no objective way to measure a person's pain, chronic pain syndrome is commonly diagnosed on the basis of a claimant's self-report alone. This raises problems for both parties. A genuine claimant may have difficulty in being believed by sceptical doctors. Solicitors and medical professionals should act with a great deal of sensitivity in these cases, because claimants suffering this debilitating condition are likely to be distressed by the allegation that their pain is not real.

Defendants may be concerned about the scale of damages that may be contemplated: the JSB guidelines indicate a top award of £40,700 in 'severe' cases, and awards can go much higher if the court accepts that there is a causal link between chronic pain and loss of earnings. In higher claims, defendants should consider instructing a separate expert to consider the issue of causation. The most appropriate medical professionals for this purpose are those with expertise in the aetiology of pain, such as some neurologists. The complexity of the causation issues involved in chronic pain cases should be a factor in a court exercising its discretion to admit a separate expert report at trial, should that be necessary (see CPR part 36, practice direction, paragraph 7).

Solicitors acting for defendants should identify at an early stage whether an action includes a claim for chronic pain. If it does, a full investigation of the circumstances should take place, with particular attention to whether any facts raise doubts over causation. Normally, these investigations should encompass the claimant's employment history, Department of Social Security reports and medical records. Any evidence that the claimant was complaining of a pre-existing condition or suffered subsequent accidents should be noted. Also important are statements regarding the nature, extent or causation of the pain, and evidence that the claimant did or did not cooperate with medical professionals during diagnosis and by undergoing recommended treatments. All of this evidence should be sent to the expert, if one is instructed, for consideration.

Finally, defendants should be fully informed by their solicitors that costs can be brought down significantly both by well-timed offers of settlement, and by offers '“ where appropriate '“ to pay for treatment (such as a pain management programme or psychotherapy) during the course of litigation. Because of the inherent uncertainties over causation in chronic pain cases, both parties should have a strong incentive to reach a mutually agreeable settlement.