By Richard Pidgeon

In AR v Accident Compensation Corporation [2023] NZCA 354 the Court of Appeal has granted leave to appeal by way of case stated, on a question of law as to whether the District and High Courts misdirected themselves on the application of Accident Compensation Corporation v Ambros [2007] NZCA 304; [2008] 1 NZLR 340.

In 2017, the applicant, now a tetraplegic, lodged a claim with ACC for a treatment injury under section 32 of the Accident Compensation Act 2001 (the Act). He suffers from GuillainBarré  syndrome (GBS)[1] which was not diagnosed for seven-and-a-half to eight hours after his mother rang an out-of-hours medical centre helpline and the nurse misdiagnosed it. The claim is based on the delay in treatment under section 33(1)(d) of the Act. 

In 2019, an ACC Review upheld ACC’s refusal to accept the claim.  The matter went on appeal to the District Court where the Reviewer’s decision was upheld[2] but leave to appeal was granted.[3]  The appeal was duly heard and the District Court decision of Judge J H Walker was upheld by Grice J in the High Court[4].

On 8 August 2023 the applicant was granted special leave to appeal to the Court of Appeal after the High Court declined leave on 12 January 2023[5]

The question of law for the appeal in the Court of Appeal is stated as:

Whether the High Court misdirected itself on the application of Ambros

by misapplying the relevant factors or overlooking relevant factors in

assessing whether the claimant had proved on the balance of probabilities

that the delay in treatment caused the claimant personal injury additional

to the injuries he would otherwise have suffered because of his

Guillain-Barré Syndrome.



The factual background is not in dispute.  In January 2017, the applicant was aged 15 years. He was on holiday and collapsed walking his dog.[6]  He made it home and his mother rang an out-of-hours medical centre in Motueka that night.  Due to incorrect medical advice, the applicant remained at home.  Early the next morning, his mother rang the out-of-hours medical centre again which resulted in an ambulance being sent and the applicant’s admission to Nelson Hospital.  Diagnosis and appropriate treatment followed once the applicant was at hospital.

The applicant was later transferred to the Intensive Care Unit at Christchurch Hospital and then the Burwood Hospital in Christchurch and remained on a ventilator for three months.[7]  He is now a tetraplegic and has to have help and support for all tasks in his daily life.  There may be some scope for improvement in the next two to three years, but this is uncertain.

The focus of the appeal in the District Court and in the High Court was therefore whether the treatment failure, being the delay in treatment, was causative of the severity of the applicant’s tetraplegia or of the GBS/ neurological injury he suffered.[8]

Three doctors gave evidence, one for the applicant and two for ACC. ACC’s Complex Claims Panel also completed a report, in which it concluded that there was no evidence that earlier treatment would have improved the outcome. The basis of the unsuccessful decisions in the District Court and the High Court was that there was no evidence to suggest the delay in diagnosis had influence on the outcome of GuillainBarré syndrome.[9] Medical causation was not proved to the required standard.[10] The High Court found that the Judge was entitled to prefer the view of the ACC’s witnesses and to come to the conclusion that legal causation was not established.[11]


Ambros Test

The Ambros test holds that a claimant has to prove on the balance of probabilities that the treatment (which includes a failure to treat) caused personal injury (not merely that it caused a risk of such injury).  Robust inferences can be drawn in individual cases.  In Ambros, the Court of Appeal confirmed that the legal approach to causation is different to the medical or scientific approach, and that the courts can infer causation in circumstances where experts cannot.[12] 

By way of background, in the High Court the applicant argued that the legal approach for considering causation based on Ambros requires the Court:[13]

(a) not be limited to expert (medical) witness evidence;

(b) consider other medical evidence;

(c) consider lay evidence;

(d) consider statistical evidence;

(e) apply a commonsense presumptive inference to the sequence of events (ie proximity);

(f) allow for a robust inference of causation in individual cases where medical science is prepared to say that there is a possible causative connection;

(g) apply a generous and unniggardly approach to drawing of a robust inference.

In granting special leave to appeal, the Court of Appeal recognised an arguable case that the District Court looked for certainty in the medical evidence when that is not the legal test for causation.[14]  Mr Miller for the applicant pointed out that Judge Walker in the District Court had not listed all the factors that were to be looked at as set out under the Ambros framework (above).[15] 

The Court of Appeal summarised the grounds of appeal in that Court as:

(a) a generous and unniggardly approach to the drawing of a robust inference of causation should automatically apply where the opportunity to determine the medical outcome was lost by the actions of the treating medical professionals;

(b) the practical experience of specialists operating in the field should be given increased weight when there is a dearth of medical literature or research on the effects of delayed treatment; and

(c) the decision maker should discuss all relevant causation factors set out in Accident Compensation Corporation v Ambros to ensure affected claimants can understand whether a generous and unniggardly approach to the drawing of a robust inference has been taken.[16]


The Special Leave Test

The test for special leave was not in dispute. In Cullen v Accident Compensation Corporation[17] the Court of Appeal stated that under section 163(2) of the Act the Court will exercise its jurisdiction if:

  • there is a serious question of law capable of bona fide and serious argument;
  • the case involves some interests, public or private, of sufficient importance to outweigh the cost and delay of a further appeal; and
  • other relevant considerations include the desirability of finality of litigation and the overall interests of justice.

The Court of Appeal in AR v Accident Compensation Corporation adopted Cullen and granted special leave to appeal.[18] The appeal is by way of case stated for the opinion of the Court of Appeal on the question of law.[19]



This decision provides a welcome opportunity for appellate guidance on the topic, with few cases reaching the Court of Appeal level.

Whether the District Court approach (upheld in the High Court) misinterpreted the test for causation as outlined in Ambros is of significant interest on the topic of medico-legal opinions and their impact on the test for causation.


[1] GBS is a motor neuron disorder where the immune system attacks the nerves.

[2] [AR] v Accident Compensation Corporation [2020] NZACC 158.

[3] [AR] v Accident Compensation Corporation [2021] NZACC 140.

[4] [AR] v Accident Compensation Corporation [2022] NZHC 1008.

[5] {AR] v Accident Compensation Corporation [2023] NZHC 10.

[6] Above n 2 at [2].

[7] Above n 4 at [5].

[8] Above n 4, at [8].

[9] Above n 2 at [267], [AR] above n 4 at [19].

[10] AR v Accident Compensation Corporation [2023] NZCA 354 at [11].

[11] Above n 10 at [11]; Above n 3 at [103].

[12] Accident Compensation Corporation v Ambros [2007] NZCA 304; [2008] 1 NZLR 340 at [67] and [70].

[13] Ambros above n 12 at [65]-[70]; [AR] above n 4 at [10]. 

[14] AR above n 10 at [12].

[15] [AR] above n 4 at [11].

[16] Ambros above n 12 at [65]-[70]; AR above n 10 at [4].

[17] Cullen v Accident Compensation Corporation [2014] NZCA 94.

[18] AR above n 10 at [3].

[19] Section 163(1) of the Act.

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