1. Diagnosing – Critical Activity HINF 371 - Medical Methodologies Session 7

2. Objective To review the process of diagnosing and factors undermining effective diangosis To review the process of diagnosing and factors undermining effective diangosis

3. Reading Mar CD, Doust J, Glasziou (2006) Chapter 4: Diagnosis, in Clinical Thinking: Evidence, Communication and Decision- Making, Blackwell Publishing and BMJ Books, USA Mar CD, Doust J, Glasziou (2006) Chapter 4: Diagnosis, in Clinical Thinking: Evidence, Communication and Decision- Making, Blackwell Publishing and BMJ Books, USA Groopman, J (2007) Flesh-and-Blood Decision Making, in How Doctors Think, Hougton and Mifflin, New York, USA Groopman, J (2007) Flesh-and-Blood Decision Making, in How Doctors Think, Hougton and Mifflin, New York, USA

4. Critical Step Being able to diagnose is a critical skill in medicine Being able to diagnose is a critical skill in medicine Further investigation, treatment and prognosis depends on the effectiveness of this step Further investigation, treatment and prognosis depends on the effectiveness of this step

5. Effectiveness of Diagnosing Depends on; Listen patients Listen patients Know which questions to ask depending on the patients Know which questions to ask depending on the patients Determine the presence or absence of the relevant clinical signs Determine the presence or absence of the relevant clinical signs Know how to identify these signs Know how to identify these signs Know which tests, if any, to order Know which tests, if any, to order

6. Diagnosing is Putting the patient in a category that we believe they are similar Putting the patient in a category that we believe they are similar However, However, Categories change Categories change New categories are developed New categories are developed ICD – 10 ICD – 10 These change because These change because Prevalence of diseases in population change Prevalence of diseases in population change Increased ability to identify (test) Increased ability to identify (test)

7. Diagnosis is important because Gives options regarding treatment and management of patients Gives options regarding treatment and management of patients Predict prognosis and response to treatment Predict prognosis and response to treatment Allows patients to categorize themselves Allows patients to categorize themselves Allows patients to manage their role in society and their emotions Allows patients to manage their role in society and their emotions

8. Three types of diagnosing Pattern recognition and feature matching: situation is familiar and diagnostic information available Pattern recognition and feature matching: situation is familiar and diagnostic information available Hypothetico-deductive reasoning: more challenging problem, 3 to 5 diagnosis at a time, collect information to confirm or exclude hypothesis Hypothetico-deductive reasoning: more challenging problem, 3 to 5 diagnosis at a time, collect information to confirm or exclude hypothesis Information gathering: not enough information to generate a hypothesis, unfamiliar or non-specific disease Information gathering: not enough information to generate a hypothesis, unfamiliar or non-specific disease

9. Diagnostic Errors Increased quantity of information (rather than quality) is related to increase rate of inaccurate diagnosis Increased quantity of information (rather than quality) is related to increase rate of inaccurate diagnosis Expert physicians collect less data but more discriminating on what to collect and they are able to generate accurate hypothesis earlier Expert physicians collect less data but more discriminating on what to collect and they are able to generate accurate hypothesis earlier Over estimation of the information gained from laboratory or imaging Over estimation of the information gained from laboratory or imaging Ordering test ‘just to be certain’ – VOMIT syndrome (victims of modern imaging technology) Ordering test ‘just to be certain’ – VOMIT syndrome (victims of modern imaging technology)

10. Diagnostic errors Missed diagnosis (false negative) Missed diagnosis (false negative) Wrong diagnosis (false positive) Wrong diagnosis (false positive) Causes Causes Disease knowledge base: recognize symptoms and link them to diagnosis Disease knowledge base: recognize symptoms and link them to diagnosis Communication skills Communication skills Examination skills Examination skills Diagnostic reasoning skills: assess baseline probability, interpret the findings, use of diagnostic heuristics, ability to recognize new symptoms to revise diagnosis Diagnostic reasoning skills: assess baseline probability, interpret the findings, use of diagnostic heuristics, ability to recognize new symptoms to revise diagnosis Organization skills: follow-up; peer-to-peer communication Organization skills: follow-up; peer-to-peer communication

11. Faults in Diagnostic reasoning 1. Faulty triggering 2. Faulty context information 3. Faulty information gathering and processing 1. Errors in assessment of disease prevalence 2. Errors in interpretation of clinical data: sensitivity and specificity, no weight of symptoms 3. Errors in application of axioms 4. Faulty verification 5. ‘No fault’ errors

12. In conclusion Both doctors and patients must accept that a certain degree of uncertainty will always be present in medical diagnosis Both doctors and patients must accept that a certain degree of uncertainty will always be present in medical diagnosis More effort required for diagnostic reasoning teaching More effort required for diagnostic reasoning teaching Increased use of probabilistic reasoning Increased use of probabilistic reasoning Use of red flag system Use of red flag system Time course of different illnesses – vascular quick development, infection inflammation in days, cancer over weeks to months Time course of different illnesses – vascular quick development, infection inflammation in days, cancer over weeks to months

13. Action thresholds Diagnosis Diagnosis Positive likelihood ratio (sensitivity/(1- specificity) >2 helpful in ruling in, >10 very good for ruling in Positive likelihood ratio (sensitivity/(1- specificity) >2 helpful in ruling in, >10 very good for ruling in Negative likelihood ratio ((1- specificity)/Specificity) <0.5 helpful in ruling out, <0.1 very good for ruling out Negative likelihood ratio ((1- specificity)/Specificity) <0.5 helpful in ruling out, <0.1 very good for ruling out Test ordering Test ordering Probability of disease <0.07 – no treatment Probability of disease <0.07 – no treatment Probability of disease >0.2 – test then treat Probability of disease >0.2 – test then treat Probability of disease >0.65 – treat Probability of disease >0.65 – treat