Sunday, October 20, 2013

Understanding the veterinary diagnostic process

I used to be an avid reader of mystery novels, such as Agatha Christie, and I used to love reading all about Holmes, and his elementary sidekick Watson. Trying to solve the mystery, to piece all of the clues together, like pieces of a jigsaw,  to come up with the solution to the whodunnit was lots of fun.

This gave me great training in what I do every day as a vet, except the whodunnit is often a "what disease process caused this" type of  mystery.  And like the crime solvers of modern times, vets, like me, do a series of tests to get more information, so we can reach the right conclusion, not just "any conclusion".  We all  know of stories when the wrong person is convicted of the crimes just so a conclusion can be reached, and we all know this is wrong, even though modern forensics acquits them eventually.

In veterinary medicine, shortcutting the diagnostic process to reach any answer, can lead to a misdiagnosis (the wrong conclusion) , which makes no one happy in the long run.

Recently, a loving pet owner, whom I met for the first time, said to me "I do not want to do any tests that are  unnnecessary".  This was said to me after examining her very sick elderly dog Terri, and explaining the tests that I would like to do to identify more what could be going on.  She was, however, very concerned about her beloved friend, and wanted to know what was wrong with her. 

Of course, as a new time visitor to Russell Vale Animal Clinic, she didn't know that I never ever

Our Lab!
recommend any tests that are not needed.  I do, however, be as thorough as possible and let owners know of all the tests or procedures that may be suitable to help me reach a diagnosis, but I would let them know which test was the best to start of with.

Once I explained the steps we take in diagnosing a pet, she understood, and we were able to work together to identify Terri's problem.  Unfortunately, the tests confirmed my initial suspicion, which was that Terri had cancer, but it also gave it a specific name too, and with that, we had good options of treatment.  

Let us be clear on what a "diagnosis" actually is - A diagnosis is the final conclusion of what the pet is afflicted with... no ifs, buts or maybes. It is 100% accurate, to the point that if the pet went to another veterinarian with similar signs and tests results, they would come up with the same diagnosis.

A "presumptive diagnosis" or "differential diagnosis" allows for the ifs, buts or maybes - it could be this, it could be that, but it is more likely than not it is "abc" disease.  A "diagnosis" and a "presumptive diagnosis" may be the same thing, or they may not be.  And this is where the danger lies - calling the presumptive diagnosis or "initial assessment" a diagnosis.... this can lead to a mis-diagnosis.  And we all know what happens when a pet (or a human) is misdiagnosed.  

So how do vets get to a diagnosis? 

There are several ways to get to the answer, with the specific steps changing depending on the situation, but it mostly falls into two main ways, which also inter-relate too.
- pattern recognition of disease
- diagnostic problem solving 

What both techniques have in common is that they always start with information about the pet, such as age and breed.  Questions are asked of the owner about what they have noticed different.  Knowing the pet's previous medical history is so important. 

With that information, we can then go and do a  full and complete hands on examination to try to find little clues as to the changes in the pet's body. We review things  such as temperature, heart rate, breathing rate and pattern, swellings in the abdomen or changes in the eyes.... we are looking for any abnormal finding to go onto our list of clinical signs.

Vets are experts in this, as they know what is normal, and thus, what is abnormal. 

Once we have our list of clinical signs and abnormalities, then we go into the next phase, and this is where it splits into the two ways of figuring out what the problem is - the "diagnosis"  the path may be  either "pattern recognition" or "diagnostic problem solving", or a even a combination of the two.

Getting back to Terri, her problem list would be
1. Not eating well for 4 days
2. Lost 1 kg in 2 weeks (about 8% of her body weight)
3. Not drinking much
4. High temperature
5. Lethargic
6. Dental disease 
7. Caudal abdominal pain with possible mass.
Pattern recognition medicine means
matching the pattern signs of disease
to a single disease.

"Pattern recognition" is used daily by all vets to diagnose common diseases which have consistent presenting signs.  All owners are guilty of using this also, when they search google for the "diagnosis" of their pet's ailments, or for when they seek or follow advice of friends or relatives on how to treat their pet's condition. For example, in our area - vets would use this way to diagnose "paralysis tick poisoning", or some acute skin conditions, such as hot spots.    

The limitations in pattern recognition is that it quickly excludes a whole raft of other possibilities for that pet's clinical signs, and thus, can easily lead to a mis-diagnosis, and thus inappropriate therapy.  In Terri's case, she came in for nausea and dramatic weight loss.   The nature of the weight loss, and where she had lost weight from,  made cancer likely, but how would you feel if, as a vet, I said to you "your pet has cancer" just based on how they look?  I know exactly what you would say, as I have said that line to clients.  "How do you know?" you would ask, quite legitimately.  Terri also could've been diabetic, or had a bowel obstruction or any other million of conditions causing the same signs.

In the situations where I have come out with the cancer assessment  upfront (although it is rare for me to do that), is based on physical examination findings that support it. But in Terri's case, whilst I might have suspected it, I didn't know for sure, and certainly, not sure enough to come out and give her the horrid "C" word diagnosis.  And I certainly would not have come up with which specific cancer she did have without further tests.  Without the specific cancer, I wouldn't know what treatment options that would've been available for her.

So that brings me to the next way - which is "diagnostic problem solving".  This can be easy or complex, depending on the particular situation.  Using this pathway, all things are considered, a logical pathway is taken until, at the end of it, a diagnosis is made (or as close to it as possible). 

We look at the problem list, and we go through each item individually, making mental notes on which organ system is involved.  We then make a determination on the most independantly signficant sign we want to "work up".  We then make a list of the potential body systems that are involved, then the possible conditions/ diseases that could affect those organs, and then systematically go through to see if they fit in with the other signs the pet may be showing. After all, everything has to fit, somehow.

Now, in some cases, this is enough to come to a diagnosis, but in most we need to gather more information, whether it be through tests or more questions of the owner or physical examination.  

In Terri's case, the most specific sign was abdominal pain with a possible mass in the caudal (near her hind legs) abdomen.  Radiographs and/or ultrasound would help define what is going on. 

The next most specific was her overall signs of general "unwellness".  Blood tests give us a insight to the internal going-ons and the Comprehensive Health Profile is a good place to start.  At 12 years of age, Terri had never had any blood tests at all (this would be like an 80 year old human, never having blood tests - unheard off in our society).  

From the loving Terri's owner's perspective, she did not want to do any tests that were not needed, but she desperately wanted to know why Terri was unwell, and what can be done to help her. 

 Unfortunately, she wanted (and hoped for)  a "pattern recognition" path of diagnosing, when Terri needed the "diagnostic problem solving" technique.  Obviously, there is a cost difference in the two aswell, and I don't doubt this factored into the owner's mind. 

As a vet, every test I do or order is never unnecessary, as it gives me information about the pet that I didn't know before, AND, that I need to know to better help understand what may be going on internally.   Even if the tests do not show up anything specific,  and haven't given us a concrete diagnosis, they still have given us information on what the pet does not have.  And like any mystery novel, that is half the battle - you go through the alibis of the suspects, and cross them out as you go along, added to the information you have, to eventually be left with the guilty one.

When owners ask me "what is the right test to diagnose my pet's condition", I usually say "it is the last test we do"... by that I mean, we may need to do a series of tests to determine what is going on, and it is usually the last test that confirms the diagnosis, ends up as the right test to do. 

As a pet and human parent myself, I do understand the frustration and worry of an unwell child or pet, and the uncertainty that comes with it.  I do understand the desire and  urgency for an immediate answer and solution.  As a vet, when many of the diagnostic steps I take are second nature to me, I may sometimes forget what it can be like from the pet parents perspective.  When I babble on about this test and that test, and the other whatsamajoobie thing that goes into something else to grab a sample, I can get so caught up in trying to get the answer to solve the mystery, I forget that you don't know how hard my brain is working to come up with a short list of possible conditions, and if needed, tests to confirm or refute these possibilities.

If at any time you, as a loving pet owner feel that I am forgetting you in this process when I am looking after your pet, you have my permission to remind me.  After all, your pet needs all of us to work together to help make them better.
Diagnosing illnesses in pets (and in people) is not always easy, no matter how it looks so on TV.  Dr Google does an awfully poor job of it too.  What I didn't talk about is my belief that helping pets is not all science and knowledge but also experience, care and empathy.

I am Dr Liz from Russell Vale Animal Clinic. Has this helped you understand a little  bit more about what we do?  I hope so.  Let me know what you think.