Safety of care

Improving patient safety and reducing risks

When common symptoms resemble rare and serious conditions

Originally published September 2015

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.

The CMPA has 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.

The College supported the care in this case. The College did not fault the family physician for failing to make the correct diagnosis, recognizing that necrotizing fasciitis is an uncommon and rapidly progressing condition, and that the patient’s symptoms were not specifically indicative of the condition. It also concluded that the diagnosis of cellulitis and the recommended treatment were reasonable based on the patient’s presenting symptoms and signs. The physician’s documentation of her care and instructions to the patient helped enable the College to assess the rationale for her treatment and follow-up plan.


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 or vivid patient diagnosis when assessing the probability of a current diagnosis

Lessons from medical-legal cases

A review of recently closed CMPA medical-legal cases over a five-year period identified 211 cases that were associated with serious, often acute, medical conditions. These included necrotizing fasciitis, brain or spinal epidural abscess, infective endocarditis, tuberculosis, and aortic aneurysm. Nearly two-thirds of the patients in these cases had severe clinical outcomes, including death and catastrophic or major disability. 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.

Risk management considerations

Physicians should remain vigilant to patients who have conditions that do not resolve as expected with treatment, who have symptoms that persist, or who do not look well despite negative investigative findings. Consider the following risk management actions, which are based on expert opinions:

  • Review all key elements of the patient’s medical record, for example, paramedic and nursing notes, emergency department notes, earlier entries, vital signs, test results, and consultation reports before establishing a diagnosis or starting treatment.
  • Provide the opportunity for the patient to fully express his or her current health concerns.
  • Incorporate clinical pathways, clinical practice guidelines, or decision tools as appropriate.
  • Consider whether additional diagnostic tests or consultations are necessary to establish or confirm the diagnosis.
  • Consider whether cognitive biases are influencing your ability to arrive at a final diagnosis.
  • For patients with continued or worsening symptoms or those who repeatedly return with unresolved complaints, re-evaluate the diagnostic assumption, repeat the physical examination, and consider alternative diagnoses, ruling out possibilities that may be life threatening.
  • Review investigative findings to ensure they correspond with the clinical impression and arrange appropriate follow-up to investigate any discrepancy.
  • Ensure protocols are in place to enable the timely receipt, effective review, and appropriate management and follow-up of investigative tests.
  • Fully record relevant information in the patient’s medical record, ensuring it reflects the medical history (including symptoms and co-morbidities), the physical examination, the investigative results, the differential diagnosis, and the rationale for the treatment plan and follow-up. Entries should be contemporaneous and written clearly and legibly.

DISCLAIMER: The information contained in this learning material is for general educational purposes only and is not intended to provide specific professional medical or legal advice, nor to constitute a "standard of care" for Canadian healthcare professionals. The use of CMPA learning resources is subject to the foregoing as well as the CMPA's Terms of Use.