What exactly is portal systemic shunt (PSS) aka liver shunt?
The portal vein in its normal state carries blood from the intestines to the liver where detoxification takes place and allows the disposal of ammonia from the body. In PSS such waste is passed directly into the main blood stream via an abnormal blood vessel or 'shunt'. You could say that PSS is basically a plumbing problem.
These abnormal blood vessels connect the portal vein to the systemic circulation, thereby bypassing the liver. This occurs because the ductus venosus (foetal vein feeding the pup prior to birth) fails to close naturally. (The usual time of closure is estimated to be at 3-4 days after birth, however interestingly one litter in the UK was tested with ultrasound one pup in the litter had closure at around 12 days, all these puppies were perfectly normal).
Types of shunts
The giant breeds are most likely to be affected with intrahepatic shunts i.e. the vessels are within the liver. The Irish Wolfhound typically gets a single left hand shunt. Being intrahepatic surgery can be difficult as much depends upon where within the liver the shunt is located. An extrahepatic shunt occurs mostly in the smaller breeds and is more easily repaired due to its accessible location. Where there are many abnormal blood vessels, this is a multiple shunt, and so far it has seemed to be inoperative. Multiple shunts are said to be acquired and are secondary to another condition.
The presence of toxins in the blood stream gives rise to the symptoms of PSS. Commonly they range from subtle signs of lack of energy, weight loss, diarrhoea, depression to signs indicative of a cerebral disorder such as episodic disorientation, ataxia, circling, dislike of light, puppy standing in a corner head to the wall, pacing, amaurotic blindness, seizures and coma.
If a puppy has a single right hand shunt, which is very rare in the Wolfhound, other symptoms like tremors, and acholic (pale) faeces have been noted (but are not the rule) and they may show symptoms earlier than puppies with a left hand shunt.
Symptoms can be gradual and are usually exhibited after the pup has eaten a meal. Because the blood supply is not being cleansed by the Liver; ammonia, which is a residue of protein and which would usually be cleansed from the blood by the liver, is pushed back into the system and the build up of ammonia leads to the symptoms.
Symptoms vary depending on the degree of the shunt. It appears that with an intrahepatic shunt it is unlikely that, if left untreated, the puppy will survive; in the case of partial shunts it has been known that the dog lives a longer, albeit, sickly life span, usually being managed with antibiotics and special low protein diet. However, these cases are in the minority and long-term prognosis has been uncertain to say the least. There are cases where the shunt isn't diagnosed until the hound is older and this may be due to partial shunting where symptoms are less obvious.
When do the symptoms show?
Some people say they can spot a shunt puppy in a litter early on, and it is true that badly affected puppies often show signs of weakness, staring coats and a general failure to thrive, as early as six weeks. However, these are in the minority and the more usual pattern is for the pup not to begin showing symptoms until after ten weeks of age.
In the case of partial shunts it has been known for a puppy to be several months old before symptoms show, due to a more gradual build up of symptoms.
Without treatment, observations have been that the dog is unlikely to survive very long, and will be in distress.
To date the most reliable method of testing for PSS is the bile acid test. Ammonia testing has proved to be an unreliable method in Wolfhounds and is not advised. Ammonia levels in Wolfhounds have been found to be naturally higher than the normal dog population and are transient.
Bile acid tests have to date been a reliable method for detecting PSS, it is stated that "Postprandial SBA concentrations are consistently abnormal and are a good screening test for animals suspected to have PSS and concentrations typically exceed 100 :mol/l" ( Ettinger).
The double bile acid test entails fasting the litter for 12 hours (usually overnight), taking a blood sample (preprandial), feeding the puppies their morning meal and then taking the postprandial sample 90 - 120 minutes after feeding.
This method is still used in cases where the result is indicative of an affected puppy or if the test is inconclusive for any reason.
After some seven years of testing in the UK we now take only the postprandial blood test. These tests are done through a dedicated laboratory who has now developed a testing index for Wolfhounds. Other breeds may need their own index as each breed can differ as to what a normal bile acid reading would be.
A puppy affected with PSS would be expected to have a post feeding bile acid reading in excess of 40, in actual fact it is usually considerably higher than the pre feeding result for example a difference from 20/155 or even 22/390 (actual readings). However there is a grey area of lower scores and one test did prove positive at only 18/44. This is in the minority (so far only one), but does highlight the need to be careful when testing, to use facilities where the vets are experienced in testing for that particular breed, and to retest if the result is uncertain.
It is impossible for any test like this to be 100% accurate but on current information it must be said that it is 99%. The main difficulties have been with the samples themselves either because the blood has clotted before reaching the laboratory.
A rarer occurrence is the some of the samples being too fatty to test. A spate of this prompted us to investigate what type of food the litters involved were being given. There was no common factor in the feeding of the litters which ranged from various complete foods to meat and rice.
Very occasionally, and I can number four occasions for this, a puppy may return a high bile acid score, but on re-test the score drops to normal levels. Again, there is no explanation for this but it does reinforce the necessity for a re-test if a positive result is returned. This is ALWAYS recommended by us and by Idexx.
Further diagnostic methods
Aside from the more accessible testing methods as mentioned above also available are rectal portal scintigraphy, ultrasonography or contrast radiography. Ultrasonography has been used in the UK to identify the location of a shunt prior to surgery, but is very dependent upon the skill of the operator. It is non invasive and does not require anaesthesia, referral by the veterinary surgeon is required. Rectal portal scintigraphy again does not require anaesthesia; it uses a radioactive substance which is rapidly absorbed from the colon into the blood stream. Radioactivity is first detected in the liver then the heart, in PSS the radioactivity reaches the heart before or at the same time as it reaches the liver. The expense and availability of equipment means that this method is only available by referral to a specialised institution. In the UK, it has recently been used in post operative care to ascertain the status of the shunt.
Surgery has to be the preferred means of repairing a shunt and has been very successful. Dietary management can help in dogs who have a partial shunt and is beneficial in reducing symptoms in dogs awaiting surgery.
Success with managing liver shunt by diet will depend on the severity of the shunt itself. Managing the condition medically includes a low protein prescription diet, usually Hills Science KD or UD. Potatoes, rice can also be included. Periodic treatment with antibiotics, and a laxative i.e. Lactulose.
Dramatic improvement can often be seen in the dog after treatment as above, but as the toxins build up again, the symptoms return and further ongoing treatment is required, it is possible that if the shunt is partial, the dog can continue a reasonably normal life with periodic treatments.
Management in this way is so far uncommon (because of the low success rate), and expensive. The highly expensive prescriptive diet is only available from veterinary surgeries and the ongoing need for antibiotics and Lactulose is also costly.
Recorded so far have been one survivor to 18 months, but died of the condition, one to 2 ½ years - died of cancer. Still surviving one bitch at 3 ½ years, only one on record made it to over 7 years, but it was stated that she was in a poor physical condition.
See below for further information on dietary management.
Surgery for the repair of a single intrahepatic shunt is now extremely successful when undertaken by an expert surgeon. Great benefit is derived from ultrasound to identify beforehand the type and location of the shunt before surgery is considered an option. The earlier the surgery is performed after diagnosis the better as this minimises damage to the liver, but a delay of two or three weeks in a young puppy i.e. eight weeks or so, will not usually be detrimental.
Total surgical ligation (i.e. the tying off of the vessel), is preferred but due to the liver being unable to cope with the volume of portal blood diverted back, causing portal hypertension, partial ligation of 60 - 80% is often opted for. The immediate post operative 24 hours is important and the dog us usually hospitalised for a few days after the operation.
Post operative care usually consists of antibiotics and diet management and lactulose. Depending on the progress of the pup, normal food can gradually be introduced after a few days, it can be expected that a normal diet can be fed on recovery. Bile acid tests can be carried out at a later date, but do not usually return to normal even when the dog becomes clinically normal.
You may read elsewhere that surgery is not that successful. This may be true in some countries or if the practitioner hasn't had a great depth of experience - this is very intricate surgery. We are very fortunate in the UK to have access to exceptional surgeons who have many years' experience now of operating successfully on many breeds - particularly Irish Wolfhounds, and this means that we have a particularly good success rate.
Contact us for details of experienced surgeons in the UK.
After successful surgery the outlook is usually excellent, there is no reason why the dog should not live a normal life, and indeed they are doing so. Surgery is extremely expensive >£2,000, it is very important that the puppy is diagnosed early for the best results from the surgery option.
Dietary Management of Liver shunt
While surgery is more often the best way of dealing with a shunt it is possible to manage the condition by diet in certain cases.
The diet follows the principle of low protein, but in the case of a growing Wolfhound puppy, gentle restriction of protein is required as long as the puppy is not showing neurological signs of the condition, otherwise growth may be hampered. Some suggested complete foods would be:
- Waltham Selected Protein
- Hills Intestinal Diet
- Eukanuba Intestinal Diet
- Wafcol Fish and Corn
- Cottage Cheese is the best source of additional protein and this can be used to supplement the diet. Avoid normal puppy foods as the protein is generally too high, you should be aiming at a level of around 20 - 24% maximum.
The protein source should be high quality for maximum digestibility. Meals should be given four times per day. The first six months are critical for growth and it is suggested that every three months protein levels are checked. This is done by taking a blood sample.
Lactulose, prescribed by the veterinary surgeon, is usually required for life. This binds ammonia and assists its elimination from the body.
Ampicillin can also be given continuously, so far no negative side effects have been observed from this.
If the puppy starts to show neurological signs, feeding Hills K/D diet can reduce the protein further. This can be supplemented with pasta/rice and cottage cheese. The Hills UD diet has insufficient protein to sustain normal growth.
Information provided by Penny Watson MRCVS - Cambridge University
If a puppy has a high score on bile acid testing Vetlab will request a retest. A second bile acid test should always be done as it is not unheard of for a high score to subsequently fall.
Please ensure that you do a DOUBLE BILE ACID TEST as this is the most effective way of confirming a positive test.
In 2007 Idexx Laboratories bought Vetlab but have agreed to continue the relationship with our breed and offer us a discounted rate on bile acid testing. This works out at £8.70 + VAT per puppy. If a puppy requires re-testing and this is usually a double test i.e. before and after feeding, this will cost £21.80 + VAT.
- Starve the puppy overnight.
- Arrange for a blood sample to be taken by the vet in the morning.
- Feed the puppy in the presence of the vet.
- Wait for 90 - 120 minutes.
- The vet should take a second blood sample.
- Clearly label the two samples as pre-feeding and post-feeding, then submit to Idexx.