Spotlight Case May 2005

1. Spotlight Case May 2005 Diagnosing Diagnostic Mistakes

2. Source and Credits • This presentation is based on the May 2005 AHRQ WebM&M Spotlight Case • See the full article at http://webmm.ahrq.gov • CME credit is available through the Web site • Commentary by: Robert McNutt, MD; Richard Abrams, MD; Scott Hasler, MD • Editor, AHRQ WebM&M: Robert Wachter, MD • Spotlight Editor: Tracy Minichiello, MD • Managing Editor: Erin Hartman, MS

3. Objectives At the conclusion of this educational activity, participants should be able to: • Understand the biases that may contribute to overcalling medical errors • Describe the impact of considering the clinical spectrum of disease presentations or alternative diagnoses on assessment of error • Appreciate the challenges inherent in assigning the label of “missed diagnosis” to a clinical scenario

4. “Overdiagnosis” of Diagnostic Mistakes • Knowledge base in safety research cannot provide definitive correlations between decisions, systems of delivery, and adverse events • Error identification schemes find error due to simple chains of events • Given complexities, redundancy and codependency are more likely • True cause and effect difficult to demonstrate McNutt RA, Abrams RI. Qual Manag Health Care. 2002;10:23-28.

5. Sources of Overcalling Error • Evaluation of a case with knowledge of the patient’s outcome (hindsight bias) • Lack of a gold standard • Failure to consider the spectrum of clinical presentations • Failure to consider the consequences of competing diagnoses

6. Case: “Doctor Don’t Treat Thyself” • A 50-year-old radiologist presented with shortness of breath and interpreted his own chest x-ray as being “consistent” with the diagnosis of pneumonia. Later the patient dies of a myocardial infarction and pulmonary edema. Several radiologists reviewed the chest x-ray (after the outcome) and reported it “consistent” with pulmonary edema.

7. WebM&M Case Analysis • The case is considered to “dramatically and tragically” illustrate a diagnostic mistake based on the assessment of radiologists who interpreted the studies after the outcome of the case was known.

8. Failure to Consider Hindsight Bias • Patient classified as low risk for adverse outcomes (0.1%-0.4% mortality) • No definitive guidelines for screening CXR in patients with a low risk score • Performance characteristics of CXR not known • Outcome of patient should not be known prior to defining diagnostic error Carthey J. Qual Saf Health Care. 2003;12(suppl 2):ii13-16.Lilford RJ, et al. Qual Saf Health Care. 2003;12(suppl 2):ii8-12.

9. Lack of a Gold Standard • Diagnostic errors difficult to call when there is no gold standard for diagnosis • Without gold standard, all diagnoses probabilistic and certainty impossible • Variation in clinical evaluation of dyspnea well established • Only “fair to good” correlation between radiographic interpretation of CXR findings of pneumonia Mulrow, et al. J Gen Intern Med. 1993;8:383-392. Badgett, et al. JAMA. 1997;277:1712-1719. Albaum, et al. Chest. 1996;110:343-350.

10. Case: “Crushing Chest Pain” • A 62-year-old woman is admitted with crushing chest pain and treated for possible myocardial infarction. She later dies of an aortic dissection and the case is presented as a diagnostic error.

11. WebM&M Case Analysis • Initial diagnosis of acute coronary syndrome reasonable due to lower base rates of competing diagnoses • “Most critical error in the case” was misinterpretation of the CXR, which revealed the tell-tale “calcium sign”

12. Calcium Sign Magnified in Radiograph

13. Failure to Consider Spectrum of Clinical Presentations • Clinical presentations of disease vary • Some noted by casual observations of widened mediastinum, while others can be missed even after utmost scrutiny • CXR findings not reliable • Diagnostic “calcium sign” very subtle in this case and required magnification • Quality of literature assessing performance of diagnostic tests for aortic dissection is poor Klompas M. JAMA. 2002;287:2262-2272.Moore AG, et al. Am J Cardiol. 2002;89:1235-1238.

14. Failure to Consider Consequences of Competing Diagnoses • Several serious diseases may explain the patient’s complaint • Empiric treatment of one increases the chance of death in another • Value of diagnostic tests to differentiate one disease from another is unknown or poorly studied

15. Failure to Consider Consequences of Competing Diagnoses • Differential diagnosis in this case includes myocardial infarction, acute coronary syndrome (ACS), pulmonary embolus, and aortic dissection (AD) • Work up for AD may delay life saving anticoagulant therapy for ACS • ACS is more likely, more harm than good may come from an overzealous attempt to not miss AD

16. Threshold Model of Decision Making • Ratio of AD to ACS is 1:250 • If AD diagnosed without delay, save a life; while delay in ACS diagnosis increases death or MI by 1% • A delay in treating ACS would kill or harm 2.5 patients with ACS while saving 1 with AD • This sort of trade-off for certainty of diagnosis is not warranted Meszaros, et al. Chest. 2000;117:1271-1278. Husted, et al. J Intern Med. 1989;226:303-310. Pauker, Kassirer. N Engl J Med. 1980;302:1109-1117.

17. Improving Diagnosis of Errors • Case evaluation should occur without knowledge of case outcome • Evaluation should be done by an independent review panel following structured format using evidence based guidelines • Classification systems for diagnosis error must incorporate methods to evaluate spectrum of illness issues Lilford RJ, et al. Qual Saf Health Care. 2003;12(suppl 2):ii8-12.

18. Improving Diagnosis of Errors • Use the threshold model of decision making • Consider explicit tradeoffs before asserting error has occurred Pauker SG, Kassirer JP. N Engl J Med. 1980;302:1109-1117.

19. Take-Home Points • When determining whether an adverse outcome represents a preventable “missed diagnosis,” ask the following questions: • Are the diagnosticians seeking a reasonable differential diagnosis? • Do diagnostic plans incorporate the risk/benefit of finding one diagnosis rather than another? • Were the appropriate tests ordered for the differential diagnosis list?