August 31, 2011

differential diagnosis - part I

     When encountering a disease like cancer, there are so many possibilities that can be encountered, that it can be mind boggling to the patient.  When the course changes paths, it can leave the patient saying, "what just happened here.  I thought we were doing A.  Now you're telling me we're doing D.  What happened to A, B and C?"
     And perhaps physicians don't do as good a job as they could at educating the patient about all that is going on.  But to be fair, the situation can be so complex, that there isn't any real good way to reduce it to layman's terms without grossly oversimplifying.  It's a tough balancing act but let me try to explain where my dad is at and why he's left in the lurch, so to speak.  It all involves the concept of a 'differential diagnosis'.  So first, I need to explain that conceptually.  I'll go into the specifics with my dad next.
     Whenever any patient presents, the first thing we're trained to do is to begin composing a differential diagnosis.  That's really just a list of all the possibilities specific to the situation.  For example, say little Johnny comes to the pediatrician with chest pain, a nasty cough, and all around just feeling poorly.  At the top of the differential diagnosis would be some type of respiratory infection, maybe pneumonia if it's really severe.  Down the list would be all sorts of other potential problems that are less likely but still possible.  We treat and rule out the most common and obvious causes first.  Tuberculosis is possible but not at the top of the list.  Now let's say that a 60-year old Johnny who's been smoking for 40 years presents with the same symptoms.  Given the patient, our differential diagnosis just changed.  Yes, we'll still include respiratory infections but now our suspicion has to include some potentially cancerous lung mass.  Or, possibly, there's an infection there on top of some other disease that has weakened the patient and made him more susceptible to the infection.
     So how does the doc even begin to communicate possibilities as wide and divergent as cancer and a simple viral infection?  One could lead to death and the other could mean being home sick for a few days.  Kind of a big difference there.  So as physicians, we're trained to keep our poker face on.  We run tests, tests, and more tests and begin to tick things off the differential diagnosis list.  And because some diseases require treatment quicker than others, we don't have the luxury of waiting until we're 100% sure.  The threshold of certainty is much lower in the real world.  Someone with acute appendicitis needs an answer pretty danged quickly.  They don't have weeks to figure it out.  But sometimes those tests can indeed take a lot of time.  And to be honest, when a medical team is chasing a viral infection and then cancer, it can appear as if they have no clue what they're doing.  It'd be a bit like going to an auto mechanic for a flat tire and coming out needing a new transmission.  And sometimes, that probably is the case.  The doc missed something critical and really is clueless.  (I doubt that to be the case with my dad.)  I won't pretend that doesn't happen.  I've seen it first hand.  But even when the team is incredibly competent, it can leave the patient feeling frustrated, confused and filled with uncertainty as to what is going on.  You kinda throw your hands up in the air and frustratedly ask, "is anyone in charge here?"  In the second part, I'll do my level best to read the tea leaves and guess at what my dad's doc had on his differential diagnosis list and what all that means.

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