The Poorly Performing Horse

And just to prove he is really doing it…

http://twitter.com/mwhiting81/status/337292298624847872

Some seriously confusing technology going on there (enough issues here coping with just the one screen…)

After the introductions and some discussion of preferred choice of snack we cracked on with the case:

Let’s start brainstorming!

First things first, work out what the problem is:

Food for thought from our fourth year lectures… (although unlikely in a racehorse, definitely a consideration for other situations…)

So our thoroughbred racehorse has started finishing poorly. What’s next?

So these are all really important questions to consider. Let’s get some answers!

Now let’s start thinking about our next steps.

What might we want to start looking at?

So, always ‘hear hooves, think horses’ – MSK issues are a very common cause of poor performance, although it’s easy to get caught up in exciting cardio and respiratory zebra conditions!

We managed to overlook this later, so I think the point is that onset of signs is a good differentiating point for possible diagnoses e.g. dynamic dorso-lateral pharyngeal collapse would pull up suddenly whilst laryngeal hemiplegia or DDSP can continue, just with poorer performance and noise!

This is also probably a good time to think about a differentials list for noise at exercise combined with poor performance:
– Laryngeal hemiplagia
– Dorsal displacement of the soft palate
– Rostral dynamic pharyngeal collapse
– Arytenoid chondritis
– Axial deviation of the aryepiglottic folds

This article is quite old, but has a useful summary and some nice pictures:  http://inpractice.bmj.com/content/22/7/370.full.pdf+html?sid=e638d881-8c96-4784-a639-1ad2bc452fde 

So, let’s make a problem list:

What next?

Getting a bit carried away (spoilt by the Gayle and Mark show)…

(DRS = dynamic respiratory endoscopy)
 http://www.acvs.org/Symposium/Proceedings2010/data/papers/026.pdf 

Ahhh, the slap test…

So the slap test is an option if we use it carefully! The idea is a slap to the withers will cause abduction of the arytenoid cartilages, which you may be able to palpate (same can be done under endoscopy, still looking for movement).

Now, there’s something else we can look at with our larynx:

A surgeon did once tell me that there were only two aspects to veterinary science, surgery and magic…

Something else very important to consider:

So we’ve had a good feel of the larynx, what other areas might we want to look at on our clinical exam?

There are two reasons for doing this:
1. There is a risk of damage to the recurrent laryngeal nerve (on the right side to cause left laryngeal hemiplegia) with jugular injections/problems

2. It could give us information if there is an underlying cardiac condition

So, jugular injections can be an issue

Let’s have a breather from the clinical stuff for a moment and think about our physiology

Another question:

Let’s dredge our brains for some first year information…

Coupling of stride and respiration

Expiration occurs as the leading leg hits the ground at the canter and gallop due to:

– Impaction of the abdominal viscera on the diaphragm

– Flexion of the neck as the forelimbs hit the ground
– Transmission of force to the chest as the forelimbs strike the ground.

All of these factors compress the thorax, aiding expiration

Nobody really wants a hypoxic horse…

There is also another important issue to consider when characterising the noise

– STRIDOR. A shrill, harsh sound, especially the respiratory sound heard during inspiration in the case of a laryngeal obstruction

– STERTOR. Snoring, sonorous respiration, usually due to partial obstruction of the upper airway

Moving on, what do we want to do with this horse?

http://twitter.com/JessfBowen/status/337296080498728961

So, we have a nice juicy laryngeal endoscopy video:

Diagnosis please!

So, we have a diagnosis of recurrent laryngeal hemiplegia. What’s the pathogenesis of this condition?

Justin Perkins found here (if you can access AVMA – afraid I can’t find it anywhere else!!):  http://avmajournals.avma.org/doi/abs/10.2460/ajvr.71.9.1003?journalCode=ajvr 

So what are our treatment options for a horse with laryngeal hemiplegia?

Whilst we’re thinking about surgery:

Let’s have a quick refresher on how we graded our horses laryngeal function:

The 4 point scale for grading laryngeal abduction
Grade 1: Symmetric, synchronous
abduction and adduction of left and right arytenoid cartilages
Grade 2: Asynchronous movement of left arytenoid
at any stage of respiration. Full abduction occurs on swallowing/nasal
occlusion
Grade 3: As for 2. EXCEPT does not
fully abduct on swallowing/nasal occlusion
Grade 4: No movement of left arytenoid cartilage

So, now we know how we are grading the condition, how does this affect how we go about diagnosing the problem?

We can slip in a bit more Justin Perkins here for his third appearance of the night!  http://onlinelibrary.wiley.com/doi/10.2746/042516409X423073/pdf 

Now for my favourite part of the session this evening – how to do a Hobday back in the good old days! Particularly fond of the deep straw bed, some speedy shaving, the tail test for unconsciousness and the ‘support’ in recovery. Definitely worth a watch!

Time for a few last questions:

PHEW.

Here are a few nice links if that still isn’t enough equine URT for you:
– Summary of RLN for owners:  http://www.ed.ac.uk/polopoly_fs/1.21239!/fileManager/rln.pdf 
– Vetstream – much more comprehensive differentials list, and links to diagnostic and surgical techniques:  http://www.vetstream.com/equis/Content/Disease/dis00316.asp 
– Summary of surgical options:  http://veterinaryrecord.bmj.com/content/150/15/481.full.pdf+html 

Thankyou again to Tom Witte (@HorseSurgeon) for another really good #vetfinals session!

See you all next week for some more cows with Wendela (@WenWapenaar), and something a little bit fancy with Mark Bowen (@MarkBowen_uon)!