# Presentation: 002441

## Spotlight Case May 2005

**Diagnosing Diagnostic Mistakes**

## 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](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

## 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

## “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.*

## 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

## 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.  *

## 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.

## 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.*

## 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.*

## 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.  *

## 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”

## Calcium Sign Magnified in Radiograph

## 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.*

## 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

## 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

## 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. *

## 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.*

**Notes:**
7. Lilford RJ, Mohammed MA, Braunholz D, Hofer TP. The measurement of active errors: methodological issues. Qual Saf Health Care. 2003;12(suppl 2):ii8-12.

## 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.*

## 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?