A 55-year-old man came to the emergency room complaining of aching chest pain radiating to the back. The pain had started the day before and recurred several times. It seemed to worsen with exertion and resolve with rest. One resting episode was associated with diaphoresis. Exam, EKG, and cardiac enzymes were normal. A portable chest X-ray showed a slightly widened mediastinum. The ER resident ordered a CT scan of the chest, and the preliminary report was negative for aortic dissection but showed a small pericardial effusion. The patient was placed on aspirin, a beta-blocker, and heparin. A cardiology consultation was called, for presumed unstable angina.<\/p>\n
I was on call and saw the patient that Saturday afternoon. After talking with him, I began to question the preliminary CT scan report. I asked an attending radiologist to go over the scan with me, and on careful review, a subtle dissection was noted. The heparin was stopped, and the patient underwent emergency aortic repair. The ER resident was stunned.<\/p>\n
\u201cWhat caused you to doubt the preliminary CT scan report?\u201d he asked. \u201cHow did you know?\u201d<\/p>\n
\u201cThe scan result just didn\u2019t fit,\u201d I said.<\/p>\n
Had I simply made a lucky guess? Perhaps. But after eliciting a history, examining the patient, and going over the other details, I formed a mental picture of the case that made me question the preliminary CT scan report.<\/p>\n
How do experienced doctors \u201csee\u201d a diagnosis and start to solve a diagnostic problem? How do we begin to generate the \u201cearly hypotheses\u201d<\/a> that I discussed in my previous post? The answer, in my view, lies in pattern recognition.<\/p>\n The Way We Detect Patterns<\/strong><\/p>\n During the first two years of medical school, we learn about causal reasoning \u2014 how basic biologic defects manifest in disease. Unfortunately, patients don\u2019t come to us with an orderly textbook description of a condition. They present with signs and symptoms, forcing us to work backward in seeking a diagnosis. The philosopher Charles S. Peirce<\/a> described this abductive reasoning<\/em> as \u201cregressing from a consequent to a hypothetical antecedent.\u201d To begin to work backward, we have to recognize a pattern. The pattern may not be clear initially, or it may lack some key parts \u2014 but eventually one does emerge, and it starts us on the path of diagnostic evaluation.<\/p>\n Pattern recognition reinforces two traditional methods in medical practice: the use of narrative and the differential diagnosis. Kathryn Montgomery discusses the use of narrative in her book How Doctors Think<\/em><\/a>. While in training, we physicians present cases repeatedly, practicing the art of developing stories that have meaning. The narratives are detailed, chronological, and structured by events. As we develop a narrative, we set ourselves up to detect patterns.<\/p>\n