Spotlight Case May 2005

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Spotlight Case May 2005

• Diagnosing Diagnostic Mistakes

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Source and Credits

• This presentation is based on the May 2005 AHRQ
  WebMM 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 WebMM Robert Wachter, MD
• Spotlight Editor Tracy Minichiello, MD
• Managing Editor Erin Hartman, MS

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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

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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.
20021023-28.
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Sources of Overcalling Error

• Evaluation of a case with knowledge of the
  patients outcome (hindsight bias)
• Lack of a gold standard
• Failure to consider the spectrum of clinical
  presentations
• Failure to consider the consequences of competing
  diagnoses

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Case Doctor Dont 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.

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WebMM 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.

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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. 200312(suppl
2)ii13-16.Lilford RJ, et al. Qual Saf Health
Care. 200312(suppl 2)ii8-12.
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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. 19938383-392.
Badgett, et al. JAMA. 19972771712-1719. Albaum,
et al. Chest. 1996110343-350.
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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.

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WebMM 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

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Calcium Sign Magnified in Radiograph
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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. 20022872262-2272.Moore AG, et
al. Am J Cardiol. 2002891235-1238.
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Failure to Consider Consequences of Competing
Diagnoses

• Several serious diseases may explain the
  patients 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

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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

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Threshold Model of Decision Making

• Ratio of AD to ACS is 1250
• 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. 20001171271-1278.
Husted, et al. J Intern Med. 1989226303-310.
Pauker, Kassirer. N Engl J Med.
19803021109-1117.
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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.
200312(suppl 2)ii8-12.
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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.
19803021109-1117.
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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?