Broadening the Differential

Feb 10 2020 (late entry)

I started the first day of my CEEP selective in the GIM Rapid Referral clinic today. After being away from medicine for the past month due to the all-consuming CaRMS process, I was both excited and nervous to restart clinical duties. Although the basics came back to me quickly, I definitely felt quite rusty.

The first case I saw was a young man who had been referred from the emergency department after an episode of hemoptysis. In reviewing the history with the patient, he had actually been experiencing a few month history of mild hemoptysis in the form of coughing up streaks of blood. However recently he had a more alarming event where he coughed up a more significant amount of blood.

I preceded to ask him questions to help build my differential and rule out the causes that commonly come to mind for hemoptysis, such as pulmonary embolism, bleeding from another source (such as the GI tract or from epistaxis), infectious causes, and malignancy. Although the patient did have some recent weight loss, which appeared to be related to improving his eating habits, there were no other associated symptoms. It did appear there was some temporal relation to his cigarette smoking and hemoptysis, although smoking alone would be unlikely to be the sole contributor to his more significant hemoptysis episode. The patient did also endorse significant marijuana use.

I presented the case to my preceptor and outlined my differential. Although I felt that certain causes of his hemoptysis such as pulmonary embolism, bleeding from another source, and tuberculosis were quite unlikely, I still did not have a clear explanation for the events other than irritation related to his cigarette smoking. My preceptor encouraged me to think more broadly about the differential and  to try and organize my list into categories.

After some teaching and discussion with my preceptor, we came up with a more comprehensive differential. We categorized this into the following:

• Thromboembolic causes, such as pulmonary embolism.
• Infectious causes, such as tuberculosis and fungal infectious. Namely due to his marijuana use, I learned he was at increased risk for aspergillosis.
• Inflammatory/Immune causes, such as sarcoidosis (given his ethnic background), Goodpasture's syndrome, granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis, systemic lupus erythematous.
• Malignant causes, such as bronchogenic cancer or carcinoid tumour.
• Genetic causes, namely hereditary hemorrhagic telangiectasia (HHT).
• And other causes, including GI bleeding, epistaxis, trauma.

After building this more thorough list, we were able to determine the best next steps for the patient, including ordering a CT chest to help investigate some of these potential causes. We also counselled the patient to maintain his smoking cessation and arranged a follow-up visit after his imaging.

As I reflected about the case, I realized I had thought of the common and/or life-threatening causes for the patient's presentation, but had forgotten to broaden my thinking to consider some of the other more rare but relevant causes. This case reminded me of the importance of constructing my differential in an organized and systematic manner in order to capture a broad yet reasonable differential. I also think that being used to the older patient population in Internal Medicine, I forgot to take into consideration the other patient characteristics in considering the differential. In this case, the patient's age, ethnic background, social history and family history also provided some clues to help build the differential. This was an extremely valuable learning case for me, not only in serving as a reminder to keep my differentials broad, but also as an opportunity to learn about new diseases. For example, I learned about the findings of aspergillosis on imaging, reviewed the physical exam findings for HHT, and discussed the classic features of GPA. I look forward to the rest of my weeks on this selective and to much more learning to come!

-MB-