How a Thoughtful Patient History Helps Build a Differential

One of the ways you will be evaluated on your internal medicine clerkship is by your ability to develop a differential diagnosis. In this post, we will focus on how a thoughtful patient history can help you formulate a differential diagnosis and ultimately guide your diagnostic and treatment plan. 

There is a saying, “A problem well-put is a problem half solved.” People rarely present with just one ailment. This makes our task difficult. Patients often have numerous chronic medical problems, but which one (if any of them) is the reason for their current discomfort? The best way to uncover the pertinent clinical problem is to obtain a thoughtful and accurate history. Let’s begin with an exercise.

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Ask with a Purpose

A 65-year-old male presents to the emergency department with a cough and dyspnea. Before you diagnose him with community acquired pneumonia, take a step back and think of questions you would ask this patient. If you are having trouble thinking of questions that is ok! You are not alone. Whenever possible, try to develop frameworks to help guide your thinking. The framework I use to guide my history taking (in addition to the reliable OLD CARTS) is the problem representation.

A problem representation is a 2-3 sentence summary of a patient’s demographics, past medical history, chief complaint, and the time course of their symptoms. Early in my training, I asked questions from a memorized list. There is nothing wrong with this approach, but it often results in a disorganized history. This makes it difficult to determine which question you are trying to answer. It also makes it challenging for your attending and team to think along with you. Having a problem representation will help you pinpoint the most important problem. It also shows that you thought carefully about the questions you asked. Asking questions in order to build a problem representation means you are obtaining a history with a goal in mind. Now that we have a framework, what questions do you have?

Let Your Curiosity Run Wild

Frameworks, while crucial, can only get you so far in developing a differential diagnosis. To build a rock-solid differential, you must use one of your most important skills: your curiosity. Think back to our example in the previous section and ask yourself, what other diseases present with fever, cough, and difficulty breathing? What if these symptoms had been present for 2 days? 2 months? 2 years? What if the patient is on immunosuppressive therapy for a renal transplant? Use your curiosity to dig deep and tease out the patient’s story. 

In this example, you let your curiosity drive your history taking, and you learned that the patient had a chronic, non-productive cough with intermittent fevers over the past 3-4 months. How does that information change your differential? This time-course would be unusual for typical community acquired pneumonia. It would however fit certain malignancies, chronic obstructive lung disease, interstitial lung diseases, autoimmune diseases, and fungal infections.  After hearing the chronicity of the patient’s complaint, you are compelled to ask more detailed review of systems questions.

“The more accurate your history, the more focused your differential diagnosis.”

Dr. Trey Richardson, Contributor, Med Student Edge

Dig Deeper

It turns out the patient has had a 15-pound unintentional weight loss, arthralgias, myalgias, and a petechial, purpuric rash on his legs. The patient also has a history of coronary artery disease requiring a coronary artery bypass, insulin dependent type 2 diabetes, and hypertension. He smoked 1 pack of cigarettes per day for 20 years. He is retired and lives in the Southeast United States. After learning this information, how does the order of your differential change? What is your problem representation for this patient? Instead of just a 65-year-old male with a cough, he is now a 65-year-old male with CAD, T2DM, HTN, and a history of smoking presenting with a chronic, non-productive cough accompanied by weight loss, fevers, arthralgias, myalgias, and a petechial rash. What is your differential now?

The Bottom Line

Developing a differential diagnosis is not just an academic exercise or an end in itself, it is a means to propose hypotheses that drive your diagnostic work-up. While obtaining a thoughtful history may take more time on the front end, the effort will pay off later. The more accurate your history, the more focused your differential diagnosis. The more focused your differential, the more efficient your diagnostic process will be. All of this ultimately translates into better patient care and more effective learning.

Do you take a thorough enough history to elucidate a well-developed differential diagnosis? What areas could you improve on in your history taking? Comment below.

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