I was taking a few students for their end-of-posting exam recently. Each of these students were assigned a patient in the ward and they were each given an hour to clerk the patient as well as perform the necessary physical examination on the patient. During the exam, the typical flow of a session would be to discuss the history, possible diagnosis and differential diagnoses and a bit on investigations.
One student was assigned a patient who had been admitted for sudden onset of left sided weakness of his body. Here was what happened during the exam:
Me: What is your provisional diagnosis?
Student: The patient had a right fronto-parietal infarct. (not the correct answer but not entirely wrong either)
Me: Do you have any other differential diagnoses?
Student: Seizure disorder.
Me: Hmmm, okay… any other?
Me: Hmm, what made you think of hypokaleimia as a diagnosis?
Student: Well, hypokaleimia is associated with limb weakness.
Me: True, but your patient only had weakness on ONE side of his body? Does that mean the potassium in his body suddenly all decided to shift to the right side, leaving the left side of his body weaker than the right?
Student: I was taught in Medicine to say “Never Say Never”!
Me: Whoever taught you that is wrong. There are certainly conditions in medicine where you cannot give diagnosis such as this. Your diagnosis of hypokaleimia to explain one sided weakness is beyond logic!
I only know of two time-tested dictum in Internal Medicine:
1. Common things are common. (Meaning, if a patient presents with fever and petechiae, I think of Dengue Fever before I think of meningococcemia!)
2. Think of one unifying diagnosis before considering two different diagnoses. Only rarely will be there be more than two diagnoses in a single patient.
As for ‘Never Say Never’, only Justin Bieber says that.