Diagnosis, diagnosis, diagnosis

Patient safety initiatives tend to focus on a rather narrow repertoire of hazards, such as falls, pressure damage and medication error. Don’t get me wrong, these are all bad things. However, there is an elephant in the room: diagnostic error. Falls very seldom lead to real harm and medication error is responsible for only a tiny proportion of cases that come to litigation.1

Diagnostic error is much more important – for example, it accounts for 63 per cent of claims against GPs in the UK.2

Litigation is only one measure of harm, but case note review confirms that diagnostic error is a major cause of preventable mortality.3

Moreover, studies of post-mortem examinations find that diagnostic error is still rife, despite all the tests that are now available to clinicians in resource-rich countries. A colleague told me recently that post-mortems are no longer necessary in an ITU setting because ITU consultants can almost always get to the bottom of a patient’s problem. Yet only a week later, a paper in BMJ Quality Safety4 showed that important diagnoses had been overlooked in 28 per cent of ITU deaths. I am not saying that all, or even the majority, of these were preventable; merely that diagnostic error is a big problem with important consequences. Certainly, diagnostic error is a plausible explanation for the weekend blip in mortality associated with empty consultant car parks.

An enormous amount of time and effort is spent on designing and monitoring the ‘patient pathway’ – doing the right things in the right order. That is all very well but what if you are on the wrong pathway? If you think a patient with a clot on the lung has pleurisy then you are going to give them anti-inflammatory instead of blood-thinning drugs. Misdiagnosis = wrong pathway = poor outcome. Guidelines and targets have a very useful purpose but they are no substitute for good, old-fashioned medical skills.

I am not the first to point out the importance of diagnostic error – Peter Pronovost is one of many who have done so.5 In the UK, Dr Caldwell referred to diagnostic errors as the most important safety problem in hospitals.6

Many causes underlie misdiagnosis. These include pressure of work and various heuristic (mental) biases, such as the famous anchoring bias that gives too much weight to the first diagnosis that comes to mind.7 However, Albert Wu found that the biggest cause of diagnostic error was simply not knowing enough medicine and therefore not thinking of the correct diagnosis – the unknown unknowns again.

Misdiagnoses are likely to arise when a common condition presents in an unusual way or where the disease is rare. Philippa Lilford and I thought it would be fun to start a collection in the latter category to which we invite you to contribute. This list is designed to identify classical ‘bear traps’ for the unwary. Here is our starter for 10, with conditions where failure to make a diagnosis can easily be fatal.

So make a suggestion or leave a comment and I will add it to the table with attribution.

Presentation ‘Bear-trap’ diagnosis Attribution
Sudden onset severe headache / backache which has improved over a few hours Leaking sub-arachnoid / abdominal aneurism Philippa and Richard Lilford
Pyrexia of unknown origin in a main-line drug user Right-sided bacterial endocartitis Philippa and Richard Lilford
Recurrent severe hypotensive sycope with virtually no other signs and symptoms Mastocytosis (but do not be like Jack Kennedy’s doctors and overlook subtle signs of Addison’s disease) Philippa and Richard Lilford
‘Flu’ followed by persistent fever, loose stools and truncal rash in a child Kawasaki’s disease Philippa and Richard Lilford
Severe headache and fever after sojourn in wild places in temperate regions of the Northern Hemisphere Lyme disease (easily treated, albeit rarely fatal) Philippa and Richard Lilford
Pyrexia of unknown origin and generalised rash, including soles of feet and palms Secondary syphilis Vicky Lilford
Fever and ‘hepatocellular’ jaundice If not hepatitis A, think leptospirosis (rats) and toxoplasmosis (cats) Philippa and Richard Lilford
Bilateral drooping eyelids when tired Myasthenia gravis BMJ “easily missed” series
Constipation starting at birth and swollen abdomen Hirschsprung’s disease BMJ “easily missed” series



1. Phillips RL, Bartholomew LA, Dovey SM, Fryer Jr GE, Miyoshi TJ, Green LA. Learning from malpractice claims about negligent, adverse events in primary care in the United States. Qual Saf Health Care. 2004; 13: 121-126

2. Silk N, What went wrong in 1,000 negligence claims. Health Care Risk Report 2000; 7: 13-15

3. Hogan H, Healey F, Neale G, Thomson R, Vincent C, Black N. Preventable deaths due to problems in care in English acute hospitals: a retrospective case record review study. BMJ Qual Saf. 2012; 22(2): 182

4. Newman-Toker D, Pronovost P. Diagnostic Errors – The Next Frontier for Patient Safety. JAMA. 2009; 301 (10): 1060-1062

5. Winters B, Custer J, Galvagno SM, Colantuoni E, Kapoor DG, Lee H, Goode V, Robinson K, Nakhasi A, Pronovost P, Newman-Toker D. Diagnostic error in the intensive care unit: a systematic review of autopsy studies. BMJ Qual Saf. 2012; 21 (11): 894-902.

6. Caldwell What is the main cause of avoidable harm to patients?  BMJ 2010;341:c4593

7. Berkeley D, Humphreys P. Structuring decision problems and the ‘bias heuristic.’ Acta Psychologica. 1982; 50 (3): 201-252


2 thoughts on “Diagnosis, diagnosis, diagnosis

  1. Pingback: Biological mechanisms of generalised brain disease such as Alzheimer’s disease and schizophrenia | Richard Lilford's Friday Blog

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