|OBJECTIVE 1: PATIENT CARE: Evaluate and manage ED patients using a prioritized differential diagnosis (for the complaints of chest pain, shortness of breath, abdominal pain, altered mental status and headache).
Differential Diagnosis and Illness Scripts
In this video we review the two processes of top-down and bottom-up thinking. So far in your medical school career, you’ve focused on bottom-up thinking. This is where you start by collecting details (via your H&P) and try to match it to a diagnosis (or diagnoses).
With top-down thinking, we do the opposite. We start with the differential and then search for corroborating details to either prove of disprove each diagnosis. This is what we use in the Emergency Department.
So once you have assembled your differential diagnosis of threats to life and limb, next you need to create the list of details for which you will search. These are the illness scripts for each diagnosis. Now you are properly armed to perform your history and physical.
Over the course of your career, You will build your illness scripts in number and level of detail. This takes years to refine, so go ahead and use a book or other resources during your rotation to make your differentials and illness scripts. Your presentations will be so much better for it.
Pre-Test Probabilities, Post-Test Probability and Test Interpretation
In this second video on EM Clinical Thinking, we look at Bayesian reasoning. Don’t worry, this name is not important but the process is. Matching your illness scripts to your history and physical, you come up with pre-test probabilities for each diagnosis. The better the match, the greater your suspicion. I like to think of four categories of matching:
- HIGH: very good match, disease is ruled-in. Start treatment, no testing needed.
- MED: pretty good match but not sure enough to start treatment, get some testing
- LOW: not so good a match, but not enough that you’re willing to rule it out. Need some testing first.
- NO: very poor match, disease is ruled out. No testing needed.
Where you set these cut-offs depends on your testing and treatment thresholds for each of the diseases on your differential.From the results, you can make your post-test probabilities. But it is important to remember, that the way you interpret a test is COMPLETELY dependent on your initial suspicion (pre-test probability). No test is perfect and your clinical thinking is better than you give it credit for.
Answer the following questions.
- Compare and contrast top-down thinking with bottom-up thinking. With which of these methods do you currently predominantly approach patients?
- Make a differential of life and limb threats for shortness of breath.
- Create an illness scripts for each of those diagnoses.
- How would you adjust your testing and treatment thresholds for each of these diagnoses?
A 62 year-old woman comes in with shortness of breath. She reports that this started suddenly approximately 1 hour prior to presentation and has progressively been getting worse. She has no chest pain. The SOB worsens with exertion and recumbency. She has no history of cancer, recent travel or immobilization, or prior DVT or PE. She has CHF, but reports she’s been compliant with her medications and diet. She also suffers for with COPD and has had no relief with nebulized albuterol. No fever or cough. She’s allergic to PCN and sunflower seeds.
Vitals: BP = 160/80; HR = 147; RR = 32; T = 100.2F; O2 sat = 82% on 100% by non-rebreather mask
On exam, she is is moderate respiratory distress speaking in broken 3-word sentences. She has mild JVD with a midline trachea. Her lungs have poor air movement with intermittent wheezing. She has 2+ pedal edema.
- Given this presentation, assign pre-test probabilities to your differential diagnoses using the categories of NO, LOW, MED AND HI.
- What tests would you like to order for each diagnosis?