Dr. André Mansoor (@AndreMansoor), associate professor of medicine in Portland, Oregon, author of the excellent Frameworks for Internal Medicine, and contributor to Physical Diagnosis PDX, talks us through a complex case of encephalopathy and respiratory failure to illustrate some principles of diagnostic reasoning.
- The hardest part of treating most diseases is making the diagnosis. Countless resources are available to assist with treatment pathways, but you won’t know which one to use if you don’t know what you’re treating. Empiric treatment is sometimes necessary in the critically ill, but it tends to obfuscate, not support diagnosis.
- Even diagnostic support tools (such as burgeoning field of artificial intelligence) will require clinicians to collect the contributory data points, such as history and physical exam findings; this still requires enough diagnostic acumen to guide the data-gathering process.
- The H&P is not “over” after the initial survey; an iterative back-and-forth process ensues between discovering diagnostic abnormalities and using them to formulate new hypotheses that direct additional, more focused questions and examination.
- Most hypoxemia is best approached by first calculating, or at least approximating, the A-a gradient. This routes you into completely different diagnostic pathways depending on the results.
- Guillain-Barré is best confirmed by lumbar puncture showing an elevated protein without pleocytosis. However, start with a physical exam suggestive of lower motor neuron disease.
- Start with a general history and exam, but after that, broad or “shotgun” testing, consultation, or empiric therapy is high in cost and complications, and just doesn’t tend to work. Formulate specific hypotheses and use your studies or consultations to test them.
- 90% of diagnoses are made from the history and physical alone. Lean on these as the cornerstone of your diagnostic process, not on high-tech tests.
- It’s reasonable to treat a patient who easily matches a standard disease script as if they have the common disease. But when they have features that appear a little different, that’s a good time to step back and work your diagnostic process methodically.