Equine Medicine : Case 2

After a successful RFM session, we moved onto the second case:

The answers started coming thick and fast:

Having developed a good set of questions, we moved on to physical exam.

The pony has digital pulses – this was picked up on and explored further to create an initial differential list for DPs:

Summary note: differentials for digital pulses
– Pedal bone (P3) fracture
– Foot abscess/area of infection
– Solar bruising
– Foot penetration injury
– Synovial sepsis to any structure within the foot (coffin, DDFT sheath, navicular bursa)
– Laminitis

However, most of these are usually only in one foot – the most common differential for pulses in multiple feet is likely to be laminitis

On a slight tangent, here is a really nice website that gives a summary of management of foot abscesses – bit of a basic guide but nice revision with videos of using hoof testers and digging out pus and a ‘recipe’ for poulticing.
 http://www.horsetrust.org.uk/advice-centre/f/foot-abscesses/ 

We also got further details on the ponies history:

This description opened up a whole new can of worms…

And some other relevant questions, firstly about coat changes:

Then on to fat deposits:

So, onto grading laminitis:

Apparently we are all a bit hazy on our Obel scale (save for Hannah!) so I will add it in here for reference (afraid I’ve been caught out by the ‘don’t worry about the detail’ quote a few too many times now [ahem…VPH…] so it’s going in!!)

Grade 0: No lameness at walk nor at a straight trot on a hard surface.

Grade 1: No lameness observable at walk, the animal moves freely. Shows lameness at trot in a straight line on a hard surface. Turns carefully.

Grade 2: The animal does not move freely at walk but moves with a “stiff” gait. Animal may show overt lameness on one leg at walk. It is reluctant to trot on a hard surface and turns with great difficulty.

Grade 3: The animal is reluctant to move at walk on any surface. It is very difficult to lift a limb. The animal may be virtually non-weight bearing on one limb.

Grade 4: The animal will not move without coercion, and is particularly reluctant to move from a soft to hard surface. It is impossible to lift a limb.

Grade 5: The animal spends most of the time recumbent, and cannot stand for more than a few minutes.

Taken from:  http://www.laminitis.org/proglaminitis.html 

We also want to decide upon the next steps to take with this case

At this point, Mark also makes a really good point about something we’ve overlooked up to this point but is very important!

Cushing’s, insulin resistance and EMS have all been mentioned, with questions on her coat and where she is depositing fat (in this case she has a cresty neck and fat pads behind the saddle area). This is really important to consider when dealing with laminitics, so here we go! How are we going to go about testing for these conditions?

Let’s start with insulin resistance:

Summary note: testing for EMS and insulin resistance

Resting serum insulin
concentration

Indicated as a screening test to detect moderate-severe IR as hyperinsulinaemia develops
Blood sample taken after 6-8h starvation (longer than this can cause a false positive due to stress)
Fasting insulinemia if >20uU/ml
False negatives with pain and stress (e.g. laminitis)

Fed insulin concentration

Fasting insulin
concentration <20uU/ml but higher post-prandial insulin responses

Three approaches:

1. Collect blood after feeding
hay
2. Perform an oral glucose
tolerance test (OGTT) with dextrose powder (1g/kg) and chaff (chaff is low
sugar)

3. Perform an oral sugar test
(OST) using a known amount of corn syrup (treacle)

Laminitis risk panel

Insulin, glucose,
triglycerol, RISQI, MIRG

RISQI – reciprocal
of inverse square root of insulin (proxy for insulin sensitivity)

MIRG – modified
insulin ratio to glucose (proxy for pancreatic output)



Combined glucose-insulin test (CGIT)

Used to detect
mild/early IR when serum insulin is
<20uU/ml

Used to quantify
insulin sensitivity and assess response to management

Challenge the animal
with exogenous glucose, then assess tissue response to exogenous insulin – both given IV, one
after the other then looking for how
rapidly the system reduces to normal

Glycaemic:
– IR if >45
minutes for glucose to fall below the baseline

Insulinaemic:
– Hyperinsulinaemia
at baseline (>20uU/ml)

– Excessive response
at 45 minutes (>100uU/ml)

And swiftly on to Cushing’s:

The use of the dexamethasone suppression test caused some controversy:

At this point we had a reminder of some important PPS skills (with the aim of avoiding the VDS…)

Summary note: dexamethasone suppression test (DST)
Take a blood cortisol pre-dex
Inject dex IV or IM
Measure cortisol at 19 or 24h

 

Normal: Suppression below
10ng/ml

HAC: Suppress and
escape

There is a very minimal risk of steroid induced laminitis, but the DST only uses a low dose so acceptable to use in the laminitic pony.




Controversy also abounded with basal ACTH:

Summary note: Basal ACTH
Positive if result
is >7.5pmol/l
However, this is affected by other factors such as seasonality (reference range only applicable outside of Autumn – normal horses can be higher than this during the Autumn!)
and pain
It is also possible to miss early disease with basal ACTH only

A quick break for a reminder of everyone’s research project favourites, sensitivity and specificity. And here is a nice little way of remembering it from one of our extended #vetfinals family!

So, back to the basal ACTH…

It turns out that this pony was started on pergolide in addition to the rest of her lami treatments.

We also need to discuss management of this case in the short term. Suggestions please!

Right, we have now radiographed this pony’s feet, and here are the images!

What are we thinking?

So these images have also raised another question:

Our interpretations are approved and a new question is posed:

And here are the suggestions!

Now, it’s getting late, on to BIG DECISION time.

All of the above summed up nicely by Fay and a classic Bowen-ism

Having decided to give her a chance, we need to consider management of the chronic laminitic

Another controversial procedure was suggested:

There was time for one last quick discussion on the use of pergolide in this case (and in general)

http://twitter.com/Helen_Wing/status/323891989215080448

Annnnnd (drumroll please) the pony survives!

The morals of the story: curly ponies have Cushing’s!

One last bit of bedtime reading for anyone who has stuck with me thus far (have a big pat on the back and some kind of celebratory snack – you deserve it!)
I am a big fan of In Practice articles in general and here are two pretty nice summaries of acute and chronic laminitis
Acute:  http://inpractice.bmj.com/content/28/8/434.full.pdf+html?sid=3577c753-4386-4abc-ada3-301c2f0268ca 
Chronic:  http://inpractice.bmj.com/content/28/9/526.full.pdf+html?sid=3577c753-4386-4abc-ada3-301c2f0268ca 

Big thanks go to Dr Mark Bowen for hosting another fab #vetfinals session – see you all next week for some cow time!