Strategies used by Doctors for Diagnosis

[This blog is part of the series which I had been writing about various aspects of Doctor - Patient Relationship. and how the function of diagnosis and treatment are at its core. In my previous blog, I had talked about why disease name identification was a very important step of the diagnosis process. This particular blog talks about what are the strategies which doctors use to diagnose.]

In my previous set of blogs in this series I had started talking about what diagnosis means from medical perspective. DiagnosisOne important realization I had was that Diagnosis is about finding the name of the disease (and the dictionary definition of Diagnosis – “process of determining the identity of (a disease, illness, etc.) by a medical examination” – also conveys the same thing) and not really about treating a patient. As commonsensical as this may sound – I have seen many do tend to miss out on this. According to me though – understanding this subtle difference is important considering that it can have a direct impact on how doctors and patients understand each other.

Now that I think I figured out what the real goal of Diagnosis process was i.e. the ‘why’ part; my next goal was to understand the ‘how’ part. Curiosity in my mind was how do doctor’s diagnose and arrive at a conclusion. Was it through a logic or some magic or by simply looking through a crystal mirror? The blog post from my brother – “What is in the Name?” gave me some insights as to what goes in the doctor’s mind during the diagnosis. My next step was to read and understand if there were any particular strategies using which doctors typically came to a conclusion.

Towards this, I thought the four-strategy model suggested by D. L. Sackett et. all. was a good starting point to start understanding how the typical clinical diagnosis happens (src – “The diagnostic process in general practice: has it a two-phase structure?” by Anders Baerheim). This blog is a summary of what those four strategies are.

Before I summarize them, I think it is important to keep in mind that these strategies are categorized based on the characteristics of the approach used in it. I do not think doctors pre-plan about the type of strategy they are going to use when they see a patient. Most of the times it is a sub-conscious decision and also there is a good chance that hybrids of these approaches are also used in real life practices. So beware – if you were to pop a question to your doc about which technique he was going to use to diagnose you – don’t be surprised if he gives you a blank stare!

So the four techniques described by Sackett et. all. are -

Pattern Recognition strategy -

Subconscious Recognition

Subconscious Recognition

While many can think about medical diagnosis as synonymous to any problem-solving technique where some kind of scientific method is applied to come to a solution, this technique of diagnosis is more instinctive especially when certain configuration of symptoms/clues appears very classical. This results in a instant/unconscious generation of a hypothesis. For example, diagnosing down syndrome after one look at the patient.

This technique of diagnosis for diseases/ailments is possibly the most common strategy/technique used by the doctors – especially the ones who are the most seasoned. More the experience of the doctor (probably clinical and not in terms of years) – better the doctor gets at this. Majority of the time this technique is reflexive and possibly not reflective. Interestingly this is not the technique which doctors are taught in their classrooms; but is learnt on patients. This technique also forms the basis for ‘first’ diagnosis majority of the time.

While Pattern Recognition strategy is the most popular strategy and majority of correct diagnosis happen around using this technique – this technique of medical diagnosis also has some inherent risks associated with it. First and foremost of course, the doctor need to be very good at the skill of looking and sensing patterns. Second, there is always a good possibility that the doctors could fail to look beyond the obvious patterns and hence there is a increased risk of doctor’s tendency to close the diagnosis prematurely. Doctors are also human beings. And like any human beings there is also the risk of introduction of self-biases possibly for self-satisfaction. Unfortunately, this technique also seems to be quite prevalent in over-stressed doctors.

Hypothetico-deductive strategy -

Probabilistic Diagnosis

Probabilistic Diagnosis

Hypothetico-deductive strategy is a type of clinical reasoning model based on a combination of both cognitive science and probabilistic theory. In this strategy, for diagnosing doctors first do a restricted rule-outs i.e. possibilities or causes which they believe the patient is not suffering from. Then they start with a short list of potential hypothesis based on the available clues. This generation of hypotheses is followed by ongoing analysis of patient information in which further data/tests are collected and interpreted (typically in a cyclical manner). Continued hypothesis creation and evaluation take place as various hypotheses are confirmed or negated.

So in some sense in this technique the diagnosis moves from a generalization (multiple hypotheses) to a specific conclusion. This technique is typically used in diagnosing uncommon or rare diseases or where the doctor may not be experienced in a particular disease.

Pitfalls associated with this technique are that doctors require a very good understanding of probability theory. They should have a good knack to work out the horses vs. zebra confusion just based on hearing the hoof-beats. This technique can also turn out to be time and cost consuming.

Algorithm strategy -

Diagnosis Algorithm for Asthama in Older People

Sample Algorithm

This type of diagnosis process is based on Clinical Guidelines/Decision Rules which are typically previously very well defined. When this approach is used, doctors typically refer to the “step-by-step IF-THEN” logic or cause-effect logic well supplemented with bundles of additional supporting information to arrive at a diagnosis. Click on the thumbnail on the right to see a sample algorithm for diagnosis of asthma in older patients. Similar algorithms are available for many such diseases where plenty of historical data is available. Today tools and software are also available to assist doctors in such strategies.

While this method is typically suggested to reduce the diagnosis errors, unfortunately in reality it is estimated that this approach is used in less than 10% of the diagnosis which takes place out there.

Complete History strategy -

Permutations and Combinations

While the Hypothetico-deductive strategy described above can be categorized as ‘diagnosis by probability’, Complete History strategy is typically exhaustion-based and can be categorized as ‘diagnosis by possibility’. This is the approach where all the possibilities are assumed. Then medical facts of the patients are collected and the assumed possibilities are eliminated one by one till the time the diagnosis is reached.

This approach is typically used for diagnosing possibilities of a rare disease or possibly when usage of any of the above listed strategy has not brought in the success of correct diagnosis. In Doctor’s community – this approach is typically considered as the method of novice, impractical, and inefficient.

I would love to hear your thoughts and/or comments!

[Src - Snapshot of the sample algorithm for diagnosis of asthma in older patients is from the article - "An algorithmic approach to diagnosing asthma in older patients in general practice" by Richard E Ruffin, David H Wilson, Sarah L Appleton and Robert J Adams; published by the Medical Journal of Australia.]

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