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A Simpler Answer – After All This Time

Magnetic resonance cholangiopancreatography demonstrating small filling defects in the distal common bile duct.

There is an allure associated with a rare diagnosis. Diagnosis momentum refers to the “stickiness” of a diagnosis once it is attached to the patient,1 and is one example of a cognitive bias that can lead to diagnostic errors. This can lead to misattribution of symptoms to a patient’s existing (even incorrect) diagnosis if clinicians do not keep their initial approach adequately broad. We present a case in which a patient with long-term misdiagnosis of a rare problem was found to have a common condition that explained her symptoms.

Case Report

A 55-year-old woman with a history of rheumatoid arthritis and a longstanding diagnosis of acute intermittent porphyria presented to the Emergency Department (ED) with acute recurrence of abdominal pain. Her history of abdominal pain dated back over 20 years, when she underwent extensive work-up and was diagnosed with acute intermittent porphyria due to an elevated erythrocyte fraction protoporphyrin and 24-hour urine coproporphyrin. She continued to have intermittent episodes of abdominal pain, at times severe enough to cause her to “black out.” She had hemin requested multiple times. She never experienced any neurological symptoms and was never re-hospitalized for this pain.

She presented to the ED in 2018 with recurrent abdominal pain attributed to her porphyria. She sought a hematologist for her worsening porphyria. Over the next 2 weeks, she was seen 3 times with abdominal pain and was given intravenous fluids, analgesia, and antiemetics, with symptom resolution. Finally, at the last ED visit, she was found to have elevated transaminases and bilirubin, as well as more focal right upper-quadrant pain that prompted an abdominal ultrasound, which revealed cholelithiasis and common bile duct dilation.

She was admitted to the hospital where endoscopic retrograde cholangiopancreatography demonstrated choledocholithiasis (Figure) and also a duodenal diverticulum possibly compressing the common bile duct. Urine porphobilinogen collected during an episode of pain was normal, effectively eliminating the possibility that acute intermittent porphyria was the cause of her abdominal pain. She underwent cholecystectomy while hospitalized, with resolution of transaminitis and hyperbilirubinemia; the diverticulum was of uncertain significance. At follow-up visits, her ultrasounds showed no ongoing inflammation and liver enzymes were normal.

Discussion

This case was challenging, not because the correct diagnosis was a complex one, but because it played out over time and involved refuting a rare diagnosis. Why did this occur? Certainly, providers who saw the patient over years had adequate knowledge about cholelithiasis, but yet “didn’t see it.” This likely had much to do with diagnosis momentum. In particular, when a disease is rare there is a tendency to attribute all symptoms to that disease and to therefore not look for alternative explanations. Gaps in knowledge due to inexperience with rare conditions can also contribute, and it is hard to identify when a symptom does not fit with the condition. The most reliable mitigation strategy for this sort of error is seeing as many cases as possible—if you’ve never seen the disease, you will never see it. Clinicians frequently use shortcuts when making clinical decisions, and usually these shortcuts serve them well.2 However, it is important that the clinician is aware of the shortcuts that impact decisions and have practical means of correcting errors that may arise due to their use. Further, it is important to have robust illness scripts even for rare conditions, so that it is possible to recognize when something does not fit.

In one of the landmark studies on the etiologies in diagnostic error, Graber et al3 identified the single most common cognitive error to be premature closure, or the failure to consider additional possibilities once a conclusion has been reached. This case highlights the importance of a physician being aware of the potential for cognitive errors and actively seeking methods to avoid them resulting in misdiagnoses. It also serves as a reminder to return to the basics when seeing a new patient.

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– Donna J. Coetzee, MPH, Gregory Vercellotti, MDa,b, Andrew P.J. Olson, MDa,b,c

This article originally appeared in the February issue of The American Journal of Medicine.

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