Diagnosis is a key role of a doctor. To quote a paper on the incidence of diagnostic error in medicine, 'Arthur Elstein, a cognitive psychologist interested in 'how doctors think' studied clinical decision making for his entire career and concluded the diagnosis is wrong 10-15% of the time. A diverse range of research approaches that have focussed on this issue over the past several decades suggest that this estimate is very much on target.'
In my specialty, acute internal medicine, the error rate in diagnosis may be even higher. We can teach doctors how to think about diagnosis, but surprisingly it is not a formal part of most undergraduate or postgraduate curricula.
Making a diagnosis is firstly about listening to a person's story (and in many cases, listening to what the eye-witness has to say as well). Studies over the last 30 or so years show that even with the explosion of medical technology and diagnostic tests, history accounts for the diagnosis at least 80% of the time. After the story, you need to understand the nature of diagnostic tests - because there is no such thing as a perfect test. You can have a normal test and have a problem, or an abnormal test and have no problem at all! You need to understand probabilities, and you need to have a bit of wisdom (and that takes experience and inclination).
Let me tell you about something that happened to a good friend of mine recently - I call stories like these 'Event Runaway' and I have seen these in hospitals a lot! My friend (let's call her 'K') had just returned from a 3 week holiday in New Zealand where she had been very well, and in fact had just completed one of the 'Great Walks' - a 3 day trek through a national park. On her return to the UK, she experienced a sudden loss of vision in one eye late at night. She thought it might be a migraine, but as K has a microprolactinoma (a small benign tumour in the hormone-producing pituitary gland), had never had this symptom before, and had been told to seek medical attention if she ever had a problem with her vision, she made a phone call. She was advised to go to the Emergency Department for a check up. Now remember K has a microprolactinoma (ie small - not enough to compress the optic nerves and cause vision problems) and suffers from migraines. The diligent junior doctor in ED listened to her story and decided to do some pituitary blood tests (why I am not sure, because K was perfectly well, and blood tests would not show whether the pituitary was enlarged and compressing the optic nerves). K's results showed a low cortisol.
Cortisol. That's a hormone that is low at night and high during the day, part of our circadian rhythm. And K had just returned from the opposite side of the world. It takes around 5 days to get the right way round physiologically after crossing 12 time zones. So despite being perfectly well, having no symptoms whatsoever of low cortisol (e.g. weakness and fatigue), and having just completed a 3 day trek across a mountain range, K was told she needed steroid replacement therapy immediately or she could die! An urgent endocrinology outpatient appointment was organised.
K questioned this at the time and asked whether the results could be explained by jet lag, but the doctors were confident. She managed to contact the endocrine team later that week. The specialist doctor did not listen to her story, but told her she should not stop taking the steroids or she could die! Around a week later, K told me this story. My eyeballs grew larger and larger in the telling, until eventually I reassured my friend she'd had a migraine and jet lag and she should stop taking the steroids - which she did, without any problem at all. Subsequent outpatient pituitary tests were (as expected) completely normal.
This comical and alarming story illustrates several principles that I'll be teaching over the next academic year, ranging from the importance of history, principles of diagnostic tests, and cognitive errors in diagnosis. I hope you enjoy learning with us!