‘Acceleration’ is condoned by the courts as an unsophisticated and not unduly analytical approach to a common situation in personal injury claims. That does not mean that the term should be used without any analysis by the expert as to what the situation on which she reports and expresses an opinion really is. 

In addressing causation of damage, the expert must provide a comparison of the likely situation as it would have been had said accident not occurred, and the situation as it now is and is likely to be in the future. This is done by applying her expertise to the evidence to provide an opinion as to the likely difference(s) of onset – both temporal and qualitative – of the symptoms as the result of the accident, and the differences in consequences for the claimant as the result of the accident.

There should be some evidential basis for this assessment of difference, whether from learned papers or from the expert’s own experience, supported by facts relevant to the claimant herself – such as age, past medical history, imaging, circumstances and severity of the accident. Most such cases will involve recognition of there being ‘a range of opinion’ and the requirements in the Practice Direction and Guidance in such cases must therefore be complied with[1]

Importance of as much precision as possible

A small difference in view as to the years of acceleration, or the manner of development of symptoms, may result in very different levels of damages being awarded, depending, for example, on the claimant’s work history and work nature. Therefore, making the assessment should be approached as scientifically as possible and in as much of an evidence-based manner as possible, despite the recognition that the use of ‘acceleration’ is an imperfect method for establishing loss.


The simple use of the term ‘exacerbation’ would suggest that the injuries, symptoms and effects that the claimant suffered as a result of their personal injury are of exactly the same type as those that the claimant would have suffered in the absence of the personal injury, but are now more severe as a result of said injury. Where more injuries have been suffered, or the symptoms are of a different nature or effect than would otherwise have been the case, this is not simply an ‘exacerbation case’ but requires a full and proper description of the difference, both in terms of symptoms and in terms of consequences.

If an expert chooses to use the shorthand term of exacerbation, then it is essential also to explain what is meant in the specific case in terms of the injuries, symptoms, effects and consequences for the claimant. Otherwise, there is the considerable danger that the expert will not communicate to the lawyer with any accuracy what she in fact means. The use of the term exacerbation alone (as with acceleration) is not sufficient or precise enough to communicate clearly the situation to the lawyers or the court, or to permit a fair assessment of damages.

To use or not to use?

There is a good argument for the medico legal expert avoiding the terms ‘acceleration’ or ‘exacerbation’ altogether, or at least using them only as the starting point for a clear description of the situation. If it is indicated that there has been an acceleration of the onset, or exacerbation in the level, of symptoms, it is then necessary to describe (and if appropriate to contrast) the difference in the onsets or nature of symptoms, the actual contrasted with the hypothetical but for the accident. 

The following is an example as to how clarity can be given to an opinion dealing with ‘acceleration’ in such a way as to allow the claim to be valued properly by the lawyers. This is not – and should never be used as – a pro-forma to be copied!

The back and neck symptoms and pain that Mr X suffered following the accident were initially severe and incapacitating. These began to diminish gradually in the weeks following the accident, so that six weeks on from the accident, Mr X was able to spend short periods out of bed and to move short distances around the ward. He returned home after 10 weeks in hospital. His neck pain and stiffness gradually resolved within 12 months of the accident, leaving him with residual back symptoms and pain that continued to settle over the next six months (i.e. 18 months post-accident). At that time, he was able to begin part time work in office-based employment, though he continues to suffer pain and stiffness that require analgesics and occasional days off work.

In the absence of the accident, Mr X would probably have suffered a gradual increase in back symptoms and pain as a result of the natural progression of the pre-existing deterioration in his lumbar spine. It is my opinion that, in the absence of the accident, the pain and restriction that he would have experienced within a period of three – six years in any event would have been commensurate with the level of residual symptoms that remains 18 months after the accident.

However, there is a both a qualitative and quantitative difference between a sudden onset of symptoms and pain as a result of trauma and the gradual onset of symptoms and pain as a result of the deterioration of a pre-existing condition. First, a sudden onset of symptoms as the result of a trauma removes any possibility that the injured person can make adjustments to ameliorate the effects resulting from the symptoms and pain. Second, the injured person, once recovered (to the fullest extent possible) usually feels more vulnerable to further injury and tends to be more risk averse in his day-to-day activities. This leads to a greater level of restriction than would be the case with similar symptoms from a pre-existing condition.

In the case of Mr X, it is probable that in the absence of the accident, with appropriate treatment and reasonable adjustments, he would have been able to continue in his full-time manual employment until about… [etc.]

[1] See Section 4.2.13 Writing Medico-legal Reports in Civil Claims – an Essential Guide

Giles Eyre is a retired barrister and an Associate Member of Chambers at 9 Gough Square, London, having practised for many years in the field of injury claims and at the interface of law and medicine. He continues to provide training and workshops for experts on providing effective expert reports and evidence, and on medico-legal issues. He is co-author of Writing Medico-Legal Reports in Civil Claims – an essential guide, and author of Clinical Practice and the Law – a legal primer, both published and sold by Professional Solutions Publishing. Giles blogs on issues relevant to court experts in civil claims at Medico-legal Minder.

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