Patient Safety Tip of the Week

January 14, 2014

Diagnostic Error:

Salient Distracting Features



Salient distracting features (SDF’s) are one mechanism by which cognitive biases may enter our diagnostic reasoning and potentially lead to diagnostic errors. These are features in a patient’s history that may be strongly associated with a disease or condition and thus catch the attention of the clinician. Particularly when reasoning in a pattern recognition mode, the clinician may be so distracted by the feature that a cognitive bias is introduced. When that SDF is not actually relevant to the patient’s case, a diagnostic error may ensue.


In our May 15, 2012 Patient Safety Tip of the Week “Diagnostic Error Chapter 3” we discussed a study from the Netherlands (Mamede 2012) looked at diagnostic reasoning in medical students and internal medicine residents. They had previously noted that salient distracting features are a major contributor to diagnostic errors, particularly when in the non-analytic reasoning mode. They showed that reflective reasoning led to significantly more correct diagnoses. Interestingly, students did not benefit from reflective reasoning. The implication is that certain salient features may attract a physician’s attention and misdirect the diagnostic reasoning process. Reflective reasoning may help overcome the influence of these distracting features.


Now the same group (Mamede 2013) has further studied the role of salient distracting features in internal medicine residents analyzing simulated cases based upon actual patients. They asked the residents to diagnose 12 clinical cases (6 simple, 6 complex) in three different formats. Some had an SDF inserted near the beginning of the case, some near the end of the case, and some with no SDF. When an SDF was presented early in a complex case there were 58% fewer accurate diagnoses than when no SDF was present. And the accuracy of diagnoses was about 50% fewer when an SDF was presented at the beginning rather than end of a case. The presence of an SDF also increased the amount of times spent making a diagnosis.


An example of a salient distracting feature in the above studies was noting early in the case that the patient had a positive PPD and family history of remote treatment for TB.


But I can provide a great personal example where salient distracting features led me astray in diagnosing myself! Several years ago I began to limp, primarily due to weakness in my left leg. It was pretty much painless except for some low-level aching in the mid-thigh region. The thigh was visibly smaller on the left than the right (measuring 2 cm. smaller in circumference). My father had died from ALS (amyotrophic lateral sclerosis). Being a neurologist, my first thoughts were, of course, that I had ALS (as many as 10% of ALS cases may have a familial component). So I went to one of my trusted colleagues for an EMG. I even informed him which muscle groups he’d likely see fasciculations, since by now I was looking for any other signs that would support a diagnosis of ALS (and almost everyone gets fasciculations from time to time that are benign in nature). How relieved I was when the EMG was normal. But that still left the limp unexplained. So we scheduled some hip X-rays. Because what little pain I had was in mid-thigh and because something in mid-thigh seemed to suddenly “catch” sometimes while walking, I insisted we also get X-rays of the thigh as well. The X-rays did show fairly significant hip arthritis on both sides. The thigh X-ray showed about a 6-inch ossification of a muscle and tendon in mid-thigh. I suspected that was likely due to a very old lacrosse injury. But it was also right where my main symptoms were located. I did at that time get my left hip injected (with both a local anesthetic and a steroid) as a diagnostic test. It produced no significant improvement. Six weeks of physical therapy led to only slight improvement. I was convinced my problem was fully related to the myositis ossificans. My limp got progressively worse. I used to walk/jog almost 8 miles a day. Now I could only walk about 2 miles a day with difficulty and could no longer jog at all. If I stood with all my weight on just the left leg, I would hear a “sproing” sound, further increasing my concern that the symptoms were related to the myositis ossificans. The literature paints a very pessimistic picture for treatment of myositis ossificans. Surgery is not likely to be helpful. There are a few case reports of symptom improvement after extracorporal shock wave therapy. Local injections with iontophoresis have also been reported to improve symptoms in some cases. I finally tracked down an orthopedic surgeon who had some experience with extracorporeal shock wave therapy. But when I saw him he took one look and said “this is all coming from that hip”. Even though I obviously understand the concept of referred pain, I still remained skeptical since I lacked the more typical hip or groin pain seen with hip arthritis. I could still kayak and I slogged through a trip-of-a-lifetime to Alaska where I was able to go on most hikes because I could use hiking poles. But I finally acquiesced to have a left total hip replacement.


My surgeon was great. The surgery went smoothly and I was out of the hospital in less than 24 hours! My thigh pain disappeared almost immediately. My rehab consisted of daily exercises at home. (I recall the “old days” when a total hip replacement patient stayed in the hospital for a couple weeks!). My limp is gone. By six weeks post-op I was cross-country skiing and by eight weeks I was downhill skiing!


My self-misdiagnosis obviously shows multiple types of cognitive bias that we commonly see in diagnostic error. Anchoring, framing, early closure and confirmation bias were all clearly operative. But very significant were the two salient distracting features (the family history of ALS and the muscle ossification on X-ray). Fortunately, my diagnostic error was not on one of my patients. And, fortunately, it didn’t lead to any significant harm. But it did have a significant impact on my lifestyle that could have been avoided if I had gone ahead with the hip replacement a couple years earlier!


In the diagnostic process we often need to step back. Most often when we do that we ask ourselves “what might I be missing?”. But just as important is to ask “what might I be giving too much weight to?” or “would I be thinking differently if {blank} was not present?”.



Some of our prior columns on diagnostic error:







Mamede S, Splinter TAW, van Gog T, et al. Exploring the role of salient distracting clinical features in the emergence of diagnostic errors and the mechanisms through which reflection counteracts mistakes. BMJ Qual Saf 2012; 21:295-300 doi:10.1136/bmjqs-2011-000518



Mamede S, van Gog T, van den Berge K, et al. Why Do Doctors Make Mistakes? A Study of the Role of Salient Distracting Clinical Features. Academic Medicine., POST AUTHOR CORRECTIONS, 25 November 2013







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