What tools do
you use to problem solve tricky cases? One of my favourite resources is a book
called Differential Diagnosis in SmallAnimal Medicine. The second edition has just come out and I gave it to
myself as an early Christmas present. In my teaching role I find that many
students struggle with the concept of problem-based medicine (PBL) or
problem-oriented medical management (POMM). Why compile a huge list of differential
diagnoses when surely there’s one right answer? I discussed this with the
authors of the second edition, Drs Alex Gough and Kate Murphy.
Putting
together this book was a huge task. For the first edition, Dr Gough compiled a
huge list of clinical signs (e.g. heart murmur), historical signs (e.g.
seizures), radiograph signs (e.g. pleural effusion), laboratory findings (e.g.
non-regenerative anaemia) and then for each of these signs scoured textbooks,
conference proceedings and papers to complete the list. For the second edition,
Kate revised, fact-checked and edited out some extraneous material. The end
product is a brilliant resource.
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Dr Kate Murphy at work. |
What is your day job?
AG: Head
of Medicine Referrals in a Multidisciplinary Referral hospital. [Ed - Alex sees referrals in medicine, cardiology and neurology; holds the Royal College of Veterinary Surgeons Certificate of Small Animal Medicine and Veterinary Cardiology and a postgraduate certificate in neuroimaging for research. He also wrote Breed Predispositions to Disease in Dogs and Cats].
KM: My day job
is balancing work and home life! At work I am the Clinical Lead for our
Referral Hospital. I work in a busy Referral Hospital, which is also the main
hospital for our First Opinion Practice. We have 13 branches sending in patients
for elective investigation and surgery and then any acute cases, which need
more care than the branches, can provide. As a result, there is never a “quiet”
day. I am a Small Animal Internal Medicine Specialist and so as well as leading
the referral team I am also actively seeing referred medical cases every day.
Some of these are straightforward (e.g. gastrointestinal investigation) and
then there are the others which is where POMM comes in!
Dr Alex Gough. |
What is POMM?
KM: POMM or
“problem-oriented medical management” is a system which makes us concentrate on
all the problems a patient has and forces us to avoid the problems of pattern
recognition which not only can lead us to misdiagnosis but can also stop us from
discovering new diseases or new presentations of old diseases.
There are so many differential diagnoses for some
signs like polydipsia and polyuria, or forelimb lameness, yet we are taught
common things occur commonly. Why bother thinking about all the potential
differentials?
AG: If you fail to consider all
the possibilities that may cause a particular sign, then you will not consider
performing the range of testing that may be required to rule in or out all the
differentials. Most of the time, if you only focus on the common diseases, you
will get away with it, but there are a lot of uncommon and rare diseases out
there, and uncommon presentations of common diseases are often seen. Taking
into account all the possible differential diagnoses makes errors in diagnosis,
sometimes catastrophic ones, less likely. For example, failing to consider that
a dog with ascites may have a pericardial effusion has led to many dogs having
unnecessary and dangerous exploratory laparotomies. That isn't to say you
should blindly test for every condition on a differential diagnosis list - this
is often suboptimal because of the invasiveness of some of the tests, as well as
financial constraints. Rather, tests should be prioritised to give the highest
diagnostic yield for the least cost (whether that is to the animal or owner),
and be prepared to revise a diagnosis if test results don't support your
diagnosis, or if an expected response to treatment is not achieved.
KM: POMM does
not stop us thinking about “common things occurring commonly” but it helps us
when we are not seeing a common case to think logically and keep our options
open. It can help us to problem solve
and then bring the most likely differentials together to aid the construction
of a sound diagnostic plan based on information we have gathered and the
finances of the client. Sometimes making assumptions leads us to select the diagnostics
most likely to give us the answer we think we will find and we might be heading
down the wrong (sometimes expensive track) because we were not prepared to
“think outside the box”.
Why are students so attracted to a "pattern
recognition" approach?
AG: The pattern recognition approach is quicker, and once it is learned, it requires less intellectual effort. It may also have some advantages, especially in simple cases, in reducing the number of tests a patient requires. For example, a limping cat with a swollen leg, pyrexia and a bite wound could be reasonably treated for a cat bite celullitis, and only if a good response to treatment is not achieved, starting testing for other problems.
KM: Pattern
recognition is easier than POMM and it is more innate. For example, a young dog
with haematemesis, haemorrhagic diarrhoea and low white blood cells is assumed
to have parvovirus infection. Such diagnosis reveals decent pattern recognition
skills but in our clinic last year we saw patients who were not infected with parvovirus
but with leptospira. Leptospirosis, would not be on many differential lists for
haematemesis and haemorrhagic diarrhoea.
Is POMM still relevant for experienced practitioners,
and why?
AG: Experienced practitioners
will often use pattern recognition, and in short consultations, this may be the
most efficient way of achieving a diagnosis. However, those cases that don't go
according to plan, or have unusual signs, can be greatly helped by going
through a logical thought process to get to the bottom of them.
KM: POMM is
used by specialist clinicians as well as experienced practitioners. You will
probably find that they do not use it for every case in its written format, but
in their heads they are running through the differentials for the presenting
problems and then rationalizing into the most likely causes, which will then be
investigated. When I see cases where I have no strong evidence for the cause, I
return to the basic POMM approach to help me logically consider all the
options.
Compiling differentials for every historical,
physical, radiographic, sonographic, laboratory and electrodiagnostic sign or
finding seems like a mammoth task - how do you do it?
The reality is that
you do have to be a little discriminatory and this is where experience helps.
So I do not write vast differential lists for non-specific signs such as
inappetance and lethargy for example. I do keep those problems on my list so
that if they do not appear to be secondary problems I push them back up my
problem solving list. When interpreting clinicopathological data one has to get
experience to decide which are significant results, which require problem
solving and which do not. Sometimes it is the fact that whilst a result is not
outside of the reference interval, it is an inappropriate finding in a
“sick/collapsed patient”. For example: a collapsed dog with low normal glucose
is an unusual finding; normally the glucose is at the top or slightly above
normal and thus this could be an indication to consider an insulinoma a likely
diagnosis. In a collapsed dog that does not have a stress leukogram, we should
consider Addison’s disease as a differential.
Do we worry
about a total white blood cell count that is 0.5x109/l above normal
– not really?
This skill is
one of the most difficult to teach and when I was teaching undergraduate
students we spent time discussing this aspect – however it is only by forcing
oneself to look at the clinicopathological data and interpret it yourself
before reading the clinical pathologist comments from the lab that will make
the clinician a better problem solver in the future. The same for
histopathology reports – read the description not just the final diagnosis. Why?….because
we are the ones who have seen the client, examined the animal and now need to
put it all together.
What is the best way to use a list of differentials?
KM: I use
differential lists to guide me rather than to dictate me. Veterinary medicine
is a science with some art thrown in. You can be an amazing POMM clinician but
the art comes in to your conversation with the client, making sure they
understand the jargon you are throwing at them, that they feel informed and
involved in the decision making for their pet and that they feel their concerns
have been listened to, respected and addressed. It is no good making the most
amazing diagnosis if the client has lost trust because you have done loads of
tests but explained nothing that they can understand or if by the time you make
the diagnosis you have spent all their money and they can not afford the
treatment. Honest, open discussion with a logical problem-orientated approach
are the keys to my clinical practice.
Thank you, Drs Gough and Murphy, for your time. Their book, Differential Diagnosis in Small Animal Medicine, is available via Wiley Blackwell here.