Thin and crumbling skulls

When a claimant alleges psychological injury, pre-existing psychological injury (PEI) evidence is often introduced to challenge or validate the claimant's case. PEI can be any type of mental anguish that pre-dates the defendant's conduct, regardless of whether it has culminated in an official clinical diagnosis. To be admissible in a legal case, PEI evidence and its use must be more probative (i.e. helpful, using the balance of probabilities) than prejudicial (i.e. excessively impacting the court's perception of the claimant's case, both in terms of causation and credibility).

When evaluating legal causation, the court can consider whether PEI provides a plausible alternative for the claimant's alleged injuries. When evaluating the claimant's credibility, the court can consider whether this PEI calls the overall veracity of the claimant's alleged injuries into question. Concealing or minimising PEI may be either unconscious (that is, an honest claimant misattributing symptoms to the defendant's conduct) or intentional untruthfulness.

Despite the prevalence of PEI in personal injury cases both in the UK and North America, the court may avoid this inquiry due to lack of knowledge of the 'eggshell skull' rules, which dictate that claimants with PEI can be fully compensated because you 'take them as you find them' (as discussed by S. Calandrillo and D. Buehler in 'Eggshell economics: A revolutionary approach to the eggshell plaintiff rule', Ohio State Law Journal, Vol. 74, pp. 375-422, 2013).

Under the assumption that PEI can be either relevant or irrelevant to the claimant's current injury claim, there should be guidelines to assist the court when evaluating the probative nature of PEI. This should be placed in the context of increasing knowledge about psychological injury.

'Eggshell claimant' rule

The 'eggshell claimant' rule provides that a defendant who causes damage should be liable for all of the claimant's injuries - in other words, taking the claimant as they finds him or her. This is generally used when:

• There is a dormant or underlying condition, revealed by the index injury;

• There is a previous condition, successfully treated, which re-emerges; or

• There is a pre-existing condition, which the defendant's negligence makes worse.

A comprehensive psychological assessment includes an evaluation of all the available information about the claimant's pre-existing, current, and prognostic/future factors. It is important to differentiate between a claimant's emotional distress resulting from the defendant's negligent actions and distress which may have inevitably developed, regardless of the defendant's role, due to their pre-existing condition.

A review of cases both in the UK and North America indicates that 'skull' rules are not applied consistently (as discussed by T. Iezzi, M.P. Duckworth, and S.R. Schenke in 'To crack or crumble', Psychological Injury and Law, Vol. 6, pp. 156 - 159, 2013), contributing to conflicting determination of cause and damages across the courts. There is need for operational definitions of the 'thin skull' and 'crumbling skull' rules and how they are effectively applied.

The characteristics of a thin skull are:

• The claimant is considered vulnerable (from earlier history); and

• They were not manifesting clinically significant symptoms or impairment.

The characteristics of a crumbling skull are:

• The claimant has experienced deteriorating health and functioning prior to the index injury, which has been accelerated by the index injury.

It is important for case law and expert assessment to:

1. Differentiate between the subtle distinctions of (a) pre-existing symptoms and (b) prior personality traits or vulnerability; and

2. Apply the 'but for' and 'material contribution' rules carefully and logically.

The defendant is responsible for the costs associated with the thin skull, but only the acceleration of the crumbling skull. The 'but for' test assesses what could be reliably predicted to have occurred in the index time frame if the index event had not occurred. The 'material contribution' test is used to apportion the cause when multiple causes are identified as having contributed to the claimant's injuries.

Determinants of cause

Determinants of cause are often complex. The following approach is recommended to determine the relevance of pre-index injury health and function, ensuring the appropriate application of the above 'skull' rules:

1. Early vulnerability which is not symptomatically evidenced immediately prior to the index accident (i.e. in the preceding six months) involves the application of the thin skull rule. This would include previous episodes of treated depression with statistical predictions of future episodes from the National Institute for Health and Care Excellence (NICE) 2009 guidelines on depression in adults.

2. When symptoms exist immediately prior to the index event and are exacerbated by the index event, then the crumbling skull rule applies.

It is important that medico-legal expert assessors demonstrate expertise and experience in evaluating claimant histories and presentation appertaining to pre-, peri- and post-injury factors (Iezzi et al, 2013), assisted by impartiality and concise focus on available information.

It is also important that solicitors, barristers, and judges have available continuing professional development opportunities which address how psychological processes such as PEI, causality, and attribution assessments operate.

For more information, see previous works by the authors, including 'Psychological injuries and legal decision making', Psychological Injury and Law (Vol. 6, 2013) by J.P. Vallano.

Dr Hugh Koch, pictured, is a chartered psychologist and director of Hugh Koch Associates. Dr Louise De Haro is also a chartered psychologist at the firm. Dr Jon Vallano is a professor in psychology at the University of Pittsburgh