Cognitive Bias and Medical Errors:

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THINK OF HORSES, AND NOT ZEBRAS, whenever you hear hoof beats. Physicians know that this saying can be a helpful reminder when formulating a diagnosis of common medical conditions.

But problems may arise in arriving at a diagnosis for some serious, but rare, medical conditions when the patient’s initial symptoms resemble those of more common and less serious conditions.

It has been found that missed or delayed diagnosis of serious medical conditions is often related to one or more of the following factors: • inadequate history and physical examination, especially in situations of multiple patient visits; • cognitive biases; and • deficiencies in the system of care. These are sources of significant risk for both patient and healthcare provider.

CASE EXAMPLE: Symptoms not indicative of serious medical condition A middle-aged man presents to a walk-in-clinic complaining of a sore throat and vomiting that started the previous day. He informs the family physician that he has been taking nonsteroidal anti-inflammatories for several months since undergoing hip surgery. The physician examines the patient and notes inflammation and slight swelling of his left ear and the left side of his neck below the ear. There is no evidence of cuts, punctures, or bruises. She confirms normal vital signs and believes the patient is in no acute distress. The physician diagnoses cellulitis and prescribes an oral antibiotic. She instructs him to return to the emergency department if there is no improvement within 24–48 hours or if his condition deteriorates.

The patient returns home, takes one dose of antibiotic and goes to bed. He dies during the night. The cause of death is acute necrotizing myofasciitis of the soft tissues of the neck. The patient’s family initiates a medical regulatory authority (College) complaint alleging the family physician failed to recognize the signs of a possibly serious infection.

Cognitive biases can impact arriving at a diagnosis Cognitive biases are distortions and short-cuts in thinking and may interfere with reaching a correct diagnosis. Types of cognitive biases include the following:

ANCHORING — focusing on one particular symptom, sign, piece of information, or a particular diagnosis, and failing to consider other possibilities

PREMATURE CLOSURE — uncritically accepting an initial diagnosis and failing to search for information to challenge the provisional diagnosis or to consider other diagnoses

ZEBRA RETREAT — backing away from a rare or uncommon diagnosis

DIAGNOSTIC MOMENTUM — sticking to a diagnostic label of a patient without adequate evidence

ATTRIBUTION ERROR — explaining the condition of patients on the basis of their disposition or character rather than seeking a valid explanation

AUTHORITY BIAS — agreeing with the “expert”

AVAILABILITY HEURISTIC — overemphasizing a recent patient diagnosis when assessing the probability of a current diagnosis

The physicians involved included emergency physicians, family physicians, and internists, as well as general surgeons and vascular, orthopaedic and neurosurgeons.

Forty-four per cent of the cases resulted in unfavourable medical-legal outcomes, usually related to a missed or delayed diagnosis. In the remainder of the cases, experts were generally supportive because they recognized the condition as difficult to diagnose.

They were also supportive when documentation reflected the rationale for the working diagnosis and the treatment plan. In the cases with a diagnostic issue, the great majority were associated with inadequate assessment and investigation.

This was attributed to the physician’s failure to: • recognize that symptoms and signs were related to a potentially serious condition • consider the condition in the differential diagnosis • appreciate the significance, severity, or worsening of the patient’s condition • review the medical record, thereby missing pertinent information • refer to a specialist or transfer to a tertiary centre • attend to the patient in a timely manner despite being notified of changes in his or her condition • reconsider the diagnostic assumption when the patient returned for multiple visits with unresolved concerns

System factors also contributed to diagnostic delay in some cases: deficient communication between physicians or with other healthcare team members (mostly about changes in the patient’s condition), and inadequate follow-up of test results. Inadequate documentation was identified in some of the cases: missing details of the physical examination, including positive or pertinent negative findings; absence of a differential diagnosis; or failing to document the advice given to the patient.

Source: CMPA Perspective September 2015 page 9.