Where does diet fit in when managing the PSS case? - Veterinary Practice
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Where does diet fit in when managing the PSS case?

LEE DANKS in this tenth in a series from Royal Canin meets a young hypoglycaemic Yorkshire Terrier who exhibits peculiar behaviour and isn’t growing as fast as she should be – diagnosis PSS

CAZ is a lovely three-monthold Miniature Yorkshire Terrier. On greeting her, you hear your receptionist exclaim about her “teacup” size. Not wanting to get involved in the semantics of such a title, you welcome Caz and her owners into the consult room.

You note her current weight is just short of 800g, a decent increase from the miniscule 380g at her eight-week puppy-check so you’re happy that some growth has occurred, but you’re not completely au fait with exactly what rate of growth is normal.

Caz presents to you exhibiting some “peculiar behaviour” which her firsttime owners don’t quite know how to interpret. She is “yappy” as you might expect from a young terrier but quite often she’s seen walking a little aimlessly and is unsteady on her feet.

She naturally gravitates to a box in a quiet corner of the living room where she is often found shivering and where occasionally a vomit has been found. “But is that normal?” your clients ask. Is it simply a matter of a young pup adapting to its new home?

Putting your hands on her you can feel that Caz has a Body Condition Score of 4/9. It transpires that her owners selected her from the litter in sympathy of her “runt” status and while they have been monitoring her weight gain, they (like you) have little knowledge of what gains would be classed as “normal”.

Her appetite has been variable on what you’d describe as a good-quality commercial food to which the owners have responded by mixing in a wet food of “mousse” consistency.

Finding little more on physical examination you note only that Caz is a little quiet in the consultation room – not what you’d expect of a young terrier. Dealing with the concerned owners, you also opt for a blood test and in-house urine analysis.

Typically ambiguous

You may already have some suspicions of what’s going on with Caz, but this is the typically ambiguous presentation for a porto-systemic-shunt (PSS) case. The hallmark signalment is all there: a small-breed terrier with questionable growth, showing signs of hepatic encephalopathy (HE).

Congenital shunts, most often diagnosed before one year of age, can come to us with more overt neurological, gastrointestinal and urinary signs 2 , testament to how many systems that the liver interacts with and how many metabolic processes rely on this organ.

Discussing paediatric reference ranges with your lab, you confirm that Caz is hypoglycaemic (puppies have lower glycogen stores and are therefore more vulnerable to the reductions in gluconeogenesis which comes with reduced hepatic function) with a microcytic anaemia, and has increased liver enzymes and high ammonia levels.

The latter are thought most responsible for HE signs; however, short-chain fatty acids, mercaptans, skatoles and indoles have also been implicated in this pathogenesis.3

Definitive diagnosis comes when your referral service identifies a portal vein-to-vena cava shunt seen outside the hepatic parenchyma on a colour flow Doppler ultrasound.

Question is, taking current status and future plans for surgical correction into account, how should we proceed with nutritional management?

The text books mention the use of antibiotics given the risk of bacteriaemia with Gram negatives from the GI tract (proceedings ref) and the role of lactulose as a fermentable fibre (moderating pH, speeding transit and trapping ammonia)7 , but what do we put in Caz’s bowl in the immediate future?

The abnormal vessels we’ve seen on ultrasound are shunting the nutrient-rich venous blood from the gastrointestinal tract (the portal circulation) directly to the systemic circulation, bypassing the liver.

Greater than 90% of the portal blood flow is redirected in most cases of congenital shunts.5 This means of course that the liver’s role in dealing with hormones, toxins and other components of metabolism aren’t realised and together, the complex of metabolic derangements (involving a number of neuro-active compounds) lead to the primary presentation: encephalopathy.

Protein-calorie nutrition

As the condition continues and the patient becomes less and less able to regulate and supply its own energy needs, protein-calorie malnutrition can set in.

Thereafter, the metabolites which come from endogenous bodily protein breakdown have been suggested to be equal (if not greater) contributors to the state of HE as are the by-products of intestinal bacterial metabolism in the colon.6

Dietary strategies in managing HE signs centre on regulating intestinal microflora and then minimising ammonia production and absorption, as this is the metabolite which is most often implicated in the neurological reaction.

In the case of Caz (and other congenital shunts) the unique nutritional requirements of the growing animal should be factored in also. Here we not only need to avoid the hypoglycaemia which will worsen the outcome 6 but provide protein and calories in excess of normal adult levels.

Many theories reflecting on dietary tolerance in humans with HE and our knowledge of which proteins (namely soy and milk) are low in heme, RNA and other nitrogenous wastes 3 have re-aligned what might be described as a “knee-jerk” reaction to avoid animal proteins in these cases.

However, it is known that dogs with congenital PSS have normal to increased dietary protein requirements6 and that serum albumin levels should be monitored as an indicator of the long-term success of dietary management. All in all we should restrict protein only to the level needed to prevent hepatic encephalopathy.

One of two diets

Transferring these theories to practice, we recommend that Caz be fed one of two diets. Hepatic formulas were developed with the PSS patient in mind and would be a good option in the short-term prior to surgery, for a couple of weeks until signs of encephalopathy are completely absent. They aim to correct malnutrition (with relatively high calories), support liver cell function and regeneration and help minimise HE complications.1

Calories come largely from a digestible carbohydrate source (rice) and a low residue soy protein source leads to fewer HE signs.4 Feeding frequent small meals has been suggested to help avoid negative energy balance and so as not to overwhelm the young dog’s digestive capacity, reducing the potential for undigested food reaching the colon.

Another option, particularly where HE signs are less overt, hypoalbuminaemia is recognised and if Caz wasn’t a good candidate for surgery, is a hypoallergenic diet.

This diet not only delivers the benefits of a vegetable protein source but includes more of it, ameliorating the concern for negative protein balance. A hypoallergenic diet is balanced for growth so as a long-term option for Caz will fit the bill nicely.

There’s no doubting that PSS cases are interesting and highlight to us the essential role of the liver in the digestive process and well beyond. When blessed with early recognition and a relatively “uncomplicated” case we’re in quite a good place for moving between medical and surgical management. Caz’s future as a yappy Yorkshire is relatively secure.

  • references and further reading list available on request.

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