By Heather Murray, MD, and Eve Purdy, MD Candidate, 2015
For many medical students, the process involved in turning a presenting complaint into an appropriate and focused differential diagnosis seems like a big black box. For clinicians who do this many times every day, the process is unconscious, and it is hard to explain to medical student learners how to break it down. Both students and teachers sometimes struggle with how to transition early medical learners to competent diagnosticians.
So, when a clinician (Heather Murray) and a second year medical student (Eve Purdy) independently stumbled across the link to a Massive Open Online Course (MOOC) on Clinical Problem Solving offered through Coursera both of us jumped at the opportunity to learn more about diagnostic reasoning. Eve registered with the hope of shedding light on the type of problem solving that she might be faced with in clerkship, while Dr. Murray registered with the intention of improving her teaching around diagnostic reasoning for students.
Though it is difficult to summarize the six-week course in one blog post there were a few takeaways from the course that we will outline. These key points might help medical students improve clinical reasoning and the same tips might help teachers in clarifying the process for learners. Much of this approach to clinical reasoning comes from the NEJM article “Educational Strategies to Promote Clinical Reasoning” by Judith Bowen (2006).
1. Organize the way you learn about diseases using Disease Illness Scripts
If you have a structured approach to the way you learn about diseases, then you will be more efficient at recalling that information and comparing diseases effectively. One way to organize information is into “Disease Illness Scripts”. This requires organizing information about the conditions into four broad categories.
|-who gets the disease?-what are the risk factors?
-making a mental picture of who you would expect to see with the disease can help
|-over what time period does the condition present?
acute on chronic
-a good way to think about this is where you would expect to see the patient (ER, vs walk-in vs family doctor)
|-what are the symptoms?
*key features are signs and symptoms that are essential to the diagnosis
*differentiating signs and symptoms are those that make this disease different then diagnoses that present similarly
*excluding signs and symptoms are those that, if present, exclude the disease
|-describe and understand the underlying disease mechanism|
2. Organize the way you think about patients using Patient Illness Scripts
When thinking about patients try to frame their presentation using the same structure as the disease illness scripts.
|What important risk factors does the patient have-age
-relevant medical history
-presentation specific risk factors i.e. recent transcontinental air travel in a patient with shortness of breath
|How long has the patient had the symptoms, have they changed?||What symptoms and clinical signs does the patient have?
-try to group as many as possible to shorten the list (e.g. group febrile, tachycardic and hypotensive as septic)
3. Compare disease illness scripts and patient illness scripts to generate a tiered differential diagnosis
Generate a differential diagnosis based on the chief complaint. You can compare your understanding about each disease on your differential with your patient using the illness scripts easily. Pay close attention to key features, differentiating features and excluding features. The closer a disease illness script is to the patient illness script the higher it should end up on your differential. Your final differential has three tiers:
Tier 1: Diseases that are those most likely belong here. The epidemiology, time course and clinical presentation are concordant with the patient illness script.
- Tier 1e: Diseases on tier 1e are diagnoses that may be less likely than tier 1 but if missed will cause immediate and serious harm. These are dangerous diagnoses! The “e” in this tier stands for “emergency” and diseases on this list must be ruled out, even if they are less likely.
Tier 2: Diseases that have some similarities to the patient illness script but aren’t a perfect fit belong here. They are still possible but less likely than tier 1 diagnoses.
Tier 3: Diseases on your original list that do not fit the illness script. They may have excluding features or lack key features.
4. Use your tiered differential to determine what tests to order
The tier that a possible diagnosis falls into will help you decide what tests to order to determine the final diagnosis. Think of each tier as a pretest probability.
Tier 1 diagnoses have a “high” pretest probability
- No tests or few tests may be needed to convince you that a diagnosis in tier 1 is responsible for the patient’s presentation and similarly you would need very convincing information to take it off your list completely.
- These and Tier 1e diagnoses should drive your initial investigations
Tier 1e diagnoses may have varying pretest probability
- These diseases may or may not be likely but regardless tests with high sensitivity are needed to rule them out (remember “SnOUT”)
Tier 2 diagnoses have a “medium” pretest probability
- Diseases on this tier are tricky. You really have to evaluate the sensitivity, specificity and information given from each test. You may need a few good tests get from a “medium” pretest probability to final diagnosis.
Tier 3 diagnoses have a “low” pretest probability
- Even relatively good tests may not move diagnoses from Tier 3 up to tier 1. The positive result that you get might be due to chance. Investigating these diagnoses should be a last resort.
These four tips won’t magically turn a medical student into an expert at clinical reasoning but they might serve to expose the way that experts think. They offer concrete ways for medical students to approach clinical reasoning and a common language for experts to discuss their approach with their learners.
For more information about MOOCs and why explicit discussion of clinical reasoning is important, see these links.
- Many MOOCs are available at Coursera on everything from jazz improvisation, to biostatistics, to the principles of cardiopulmonary resuscitation and everything in between.
- “Teaching Clinical Reasoning” by Michelle Lin (@M_Lin) at Academic Life In Emergency Medicine
- “Teaching Clinical Reasoning” by Nadim Lalani (@ERMentor)
- “Thinking about teaching thinking” by Robert Centor (@medrants)
- Lauren Westafer’s (@LWestafer) great medical student thoughts on “Thinking About Thinking” and “Metacognition for the Pragmatist”
- For a review of the Course and thoughts about how it might be applied to Facilitated Group Learning at Queen’s see Eve’s blog posts here and here.
- MOOC’s as they relate to Free Open Access Medical Education, “What is a MOOC” by Chris Nickson (@precordialthump)