ABSTRACT OF THE WEEK

The Veterinary record
Volume 190 | Issue 10 (May 2022)

Diagnostic value of liver function tests and ultrasonography in dogs with suspected congenital portosystemic shunts.

Vet Rec. May 2022;190(10):e1381.

Nausikaa Devriendt¹, Goncalo Serrano², Emmelie Stock³, Dominique Paepe⁴, Hilde de Rooster⁵

¹ Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.; ² Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.; ³ Department of Medical Imaging of Domestic Animals and Small Animal Orthopaedics, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.; ⁴ Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.; ⁵ Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.

Abstract

BACKGROUND:Diagnosing a congenital portosystemic shunt (cPSS) in dogs can be challenging. The current study aims to report diagnostic performance of fasting ammonia (FA), preprandial, postprandial and paired serum bile acids (SBA) and abdominal ultrasound (aUS) in dogs suspected of having a cPSS.

METHODS:Medical records of dogs suspected of having a cPSS at initial presentation were retrospectively reviewed.

RESULTS:In total, 192 dogs suspected of cPSS were included: a cPSS was confirmed in 147 dogs and excluded in 45 dogs. FA had the best combined sensitivity and specificity (77.4 and 93.3%, respectively) to diagnose cPSS. The sensitivity and negative predictive value were 100.0% for paired SBA, making paired SBA the best test to exclude cPSS in this population. Sensitivity and specificity of aUS were 80.8 and 90.0%, respectively.

CONCLUSIONS:In dogs with clinical signs compatible with cPSS, elevated FA is suggestive of cPSS, whereas normal paired SBA makes the presence of a cPSS unlikely. Although aUS is a useful tool to diagnose cPSS, additional imaging is required to visualize cPSS in almost 20% of cases. Furthermore, the localisation of cPSS can be misdiagnosed, especially in case of extrahepatic cPSS that do not insert into the prehepatic vena cava.

Companion Notes

Retrospective report on the diagnostic value of liver function tests and ultrasonography in 192 dogs with suspected congenital portosystemic shunts

Introduction on congenital portosystemic shunts (cPSS)

- congenital aberrant vessels connecting the portal system directly to systemic circulation

- resulting in portal blood to bypass the liver parenchyma

- liver remains small

- can’t produce normal amounts of important metabolites

- glucose

- albumin

- urea

- can’t adequately detoxify blood from GI tract and systemic circulation

- these aberrant vessels are typically single vessels

- localized intrahepatically (cIHPSS) or extrahepatically (cEHPSS)

- reported prevalence in dogs in the general population” 0.18–0.76%

- clinical signs are often vague and typically consist of the following:

(typically seen at a very young age)

- growth retardation

- gastrointestinal signs such as hyporexia, weight loss and vomiting

- polydipsia and polyuria

- urinary tract signs secondary to ammonium urate urolithiasis

- neurological signs related to hepatic encephalopathy

- diagnosis can be challenging

- main differential diagnosis is portal vein hypoplasia, also a congenital disease

- involves microscopic intrahepatic portovenous shunting

- most commonly used liver function tests in dogs suspected of cPSS

- fasting ammonia (FA)

- reported sensitivities to diagnose portosystemic shunting: 85-98%

- reported specificities to diagnose portosystemic shunting: 86-90%

- ammonia tolerance test

- serum bile acids (SBA)

- reported sensitivities and specificities

- sensitivities of preprandial SBA: 89-98%

- specificities of preprandial SBA: 58-68%

- sensitivity of postprandial SBA: 100%

- specificity of postprandial SBA: 100%

- studies cited above had little to no uniformity in the following:

- composition of the diseased group and/or of the control group

- results, therefore, are difficult to compare and interpret

- diagnostic imaging plays an important role

- abdominal ultrasound (aUS) is the most commonly used technique

- can rule out other differential diagnoses

- results are very much operator dependent

- alternative imaging techniques

- computed tomography angiography (CTA)

- magnetic resonance angiography (MRA)

- portal scintigraphy

- evaluates the distribution of radioactive pertechnetate

- injected into the spleen (transsplenic portal scintigraphy, TSPS)

- administered intrarectally (per-rectal portal scintigraphy)

- considered to have a high sensitivity for detection of cPSS

- less expensive than CTA and MRA

- anatomical detail is poor

- special veterinary facilities required

Study design

- study population: dogs seen at Ghent University

- 192 dogs suspected of having a cPSS

- procedure: records between 01/10 until end of 03/20 retrospectively reviewed

- dogs were placed into 1 of 2 groups

- group 1: cPSS identified on CTA or TSPS or confirmed on surgery

- history and signalment of the 147 dogs

- breeds represented by 4 or more cases

- Yorkshire terrier, 24

- Maltese, 13

- cross-breed, 12

- dachshund, 10

- chihuahua, 9

- pug, 7

- Jack Russell terrier, 7

- Bichon Frisé, 6

- golden retriever, 5

- shih tzu, 4

- miniature pinscher, 4

- median age: 10 months with a range of 2-128

- median weight: 4.6 kg with a range of 0.9-29.3 kg

- sex:M, 79 cases (20 were neutered)

- extrahepatic PSS, 122 dogs

- 83 could be further sub-divided

- portocaval, 60

- portoazygos, 13

- portophrenic, 10

- intrahepatic PSS, 22 dogs

- group 2: dogs suspected of cPSS

- cPSS subsequently ruled out by either CTA, TSPS or during surgery

- clinical signs included the following:

- lethargy

- growth retardation

- GI signs

- polydipsia and polyuria

- abnormal behavior

- tremors

- seizures

- exclusion criteria:

- dogs with acquired PSS

- dogs in which a cPSS could not be confirmed or ruled out

- diagnostic performance of the following assessed

- fasting ammonia (FA)

- measured in-house on 1 of the following:

- hand-held device (Pocket Chem BA, A. Menarini Diagnostics)

- non-portable chemistry analyzer (Catalyst Dx, IDEXX Laboratories)

- preprandial, postprandial and paired serum bile acids (SBA)

- for paired SBA, test considered positive if either of the following present

- preprandial or postprandial SBA were elevated

- both pre and postprandial SBA were elevated

- abdominal ultrasound (aUS)

Results

- cPSS confirmed in 147 dogs and excluded in 45 dogs

- diagnostic utility of the 3 tests in diagnosing cPSS assessed

- FA

- best combined sensitivity and specificity

- sensitivity: 77.4%

- specificity: 93.3%

- results in the 147 dogs with cPSS

- increased, 89 cases

- normal, 26

- not determined, 32

- results in the 45 dogs with cPSS excluded

- increased, 2 cases

- normal, 27

- not determined, 16

- paired SBA

- sensitivity and negative predictive value: 100.0%

- best test to exclude cPSS

- specificity:

- 66.7% using optimal cutoff

- using ROC curve using index of union method

(ROC = receiver operating characteristics)

- 16.7% using current cutoff based on currently available values

- aUS

- sensitivity: 80.8%

- specificity: 90.0%

- central divisional cIHPSS wrongly identified as cEHPSS, 2 dogs

- insertion of cPSS incorrectly identified, 2 dogs

“Pre and postprandial SBA, when evaluated in isolation, had similar sensitivities (94.1 and 94.4%, respectively) but the NPV [negative predicting value] was higher for preprandial compared to postprandial SBA (70.0 and 62.5%, respectively).”

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