Congenital Extrahepatic Portosystemic Shunt in a Yorkshire Terrier

Signalment, History, and Presentation

Autumn, a 5-month-old, 1.36-kg (2.2-lb), intact female Yorkshire terrier, was presented to the clinic for disorientation, lethargy, and anorexia. The owner stated that on the previous evening Autumn appeared confused and not herself. She was restless and circling with jerky movements. However, she was very active and playful, with a good appetite, the day before. The owner mentioned that Autumn would at times have episodes of disorientation after eating. Her diet had been switched to high-protein meals 3 weeks prior to presentation. The owner confirmed that Autumn was not exposed to any toxins, foreign materials, or medications, and no rodent or insect baits were in the home. An imidacloprid and flumethrin flea and tick collar was placed on her 3 weeks prior.

Physical Exam Findings

Upon physical examination, Autumn was quiet, alert, and responsive but disoriented. Rectal temperature was 38.4 °C (101.1 °F), heart rate was 100 beats/min, and respiratory rate was 28 breaths/min with normal effort. No abnormal heart or lung sounds were auscultated, and peripheral pulses were adequate and synchronous. Mucous membranes were pink, capillary refill time was 1 to 2 seconds, and hydration was normal. Autumn had most of her adult dentition, except the maxillary; bilateral deciduous canines were still intact, with adult canines slightly erupting. Her abdomen was soft and nonpainful, and her body condition score was 4/9.

Neurologic examination revealed forebrain ataxia, circling left and right in a jerking motion, intact thoracic and pelvic limb reflexes, adequate range of motion in the neck, and no indication of cervical or back pain. Both pupils were miotic with a positive menace and palpebral responses; pupillary light reflexes were within normal limits. Autumn appeared uncomfortable, very restless, and not eager to interact with people or surroundings. Her pain score was graded 2/4 based on the Colorado State University Canine Acute Pain Scale (bit.ly/46GrIIg).

Diagnostics

During the examination, Autumn urinated on the floor, and a urine sample was collected. A urine cytology performed in house confirmed ammonium biurate crystals. An IV catheter was placed and blood was collected for in-house diagnostics. Autumn’s blood glucose reading was normal at 101 mg/dL (reference range, 73 to 116 mg/dL), packed cell volume was 45% (reference range, 37% to 55%), and total protein was 6.8 g/dL (reference range, 5.2 to 7.8 g/dL).^1,2 An in-house analyzer was used to obtain a complete blood count (CBC), and results were within normal ranges. However, serum biochemical results revealed elevated alkaline phosphatase (ALP) at 303 IU/L (in-house biochemical analyzer reference range, 20 to 150 IU/L), signifying increased liver production, and elevated alanine aminotransferase (ALT) at 486 IU/L (in-house biochemical analyzer reference range, 10 to 188 IU/L), indicative of hepatic cell damage.³

An abdominal ultrasound was performed, revealing a diffusely normal liver, a large gallbladder with normal wall structure and anechoic contents, and an abnormal finding of a dilated vessel with blood flow in the left cranial quadrant between the liver and the stomach; findings were consistent with a portosystemic shunt.

Autumn’s symptoms included lethargy, anorexia, disorientation, ataxia, circling, and tremors. Differential diagnoses included a portosystemic shunt, hepatic encephalopathy, vestibular disease, hypoglycemia, and seizures, with neoplasia less likely.

Treatment Plan

IV fluids were started with lactated Ringer’s solution (LRS) at a rate of 90 mL/kg/day. Maropitant citrate was administered at 1 mg/kg IV q24h, metronidazole at 7.5 mg/kg IV over 30 minutes q12h, and ampicillin at 10 mg/kg IV q8h. A 30-mL enema mixture of 7 parts warm water and 3 parts lactulose was given q12h. Autumn remained hospitalized overnight for continued treatment and stabilization.

The next day, Autumn was bright, alert, and responsive and appeared less disoriented. She was no longer circling but was still making slight jerking motions. She continued to be monitored for worsening signs throughout the day; changes in mentation or any abnormal behavior were noted. A brief neurologic assessment revealed good range of motion in the neck, no cervical or back pain, and conscious proprioception; all limbs were noted to be ambulatory. Autumn’s numerical pain score was graded 0/4; she was comfortable when resting, seemed happy and content, and was interested in people. Injectable medications were continued at the same doses, except lactulose was administered at 2 mL PO q12h.

The owner was informed of Autumn’s improvement from treatment, and the veterinarian was comfortable discharging her. It was discussed that Autumn would need to be stable for at least 2 weeks before an exploratory surgery could be performed to repair the shunt. The owner was instructed on the importance of diet changes specific to hepatic support that would be beneficial over the long term. Autumn was to be fed a low-protein therapeutic diet or offered home-cooked meals with vegetables and dairy protein, such as butternut squash and low-fat cottage cheese, with no red meat. Her daily energy requirement (DER) was calculated to be 221.6 kcal/day, based on a resting energy requirement (RER) for puppies. Lactulose would be given indefinitely, and she was sent home with metronidazole to be given at 7.5 mg/kg PO q12h and S-adenosyl-L-methionine (SAMe) at 90 mg PO q24h 1 hour before eating. A recheck examination was scheduled in 1 week to follow up on her progress and obtain blood analysis for fasting and postprandial bile acids, CBC, serum biochemical profile, and coagulation profile to evaluate prothrombin time (PT) and partial thromboplastin time (PTT) prior to surgery.

Outcome

Autumn returned for her recheck appointment the following week. The owner stated Autumn was doing well at home and taking the medications as prescribed; however, bowel movements were producing soft stool, and Autumn preferred home-cooked meals and butternut squash baby food. Blood was collected and submitted to an external laboratory for further diagnostics. The owner was instructed to continue the metronidazole, lactulose, and SAMe supplement as prescribed. Pending lab results, surgery was scheduled in 3 weeks at a referring hospital to perform an abdominal exploration, liver biopsy, hepatic shunt repair, and ovariohysterectomy.

Both fasting and postprandial bile acids concentrations were elevated, indicating hepatobiliary disease. Fasting concentration was measured at 70.9 µmol/L, with postprandial measuring at 130 µmol/L. Liver enzymes were also elevated on serum biochemical profile; ALT was measured at 530 IU/L and ALP at 405 IU/L. CBC and PT/PTT were within normal ranges (TABLE 1).

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The surgery was performed as scheduled. The abdominal exploration revealed the location of the hepatic shunt and an ameroid constrictor was placed on the shunt; the constrictor would gradually reduce the flow of blood and eventually close the vessel entirely. Several tissue samples of the liver were submitted to an external laboratory for evaluation. An ovariohysterectomy was also performed. Autumn remained overnight at the referral hospital for monitoring and was discharged the following day. She was sent home with oral medications: amoxicillin trihydrate/clavulanate potassium to be given at 62.5 mg/kg q12h for 14 days, zonisamide at 60 mg/mL q12h, gabapentin at 75 mg/mL q8h, and the metronidazole and lactulose to be continued as prescribed. It was recommended that a repeat bile acids test be completed within 2 to 3 months for evaluation of the liver and gallbladder values to consider a diet change and possibly discontinue medications.

Discussion

Results of the liver biopsy revealed severe arteriolar reduplication that confirmed the diagnosis of a portosystemic shunt (BOX 1). Autumn’s final diagnosis was hepatic encephalopathy secondary to an extrahepatic congenital portosystemic shunt (CPSS).

A CPSS can occur through 1 or more connections at a microvascular or macrovascular level between the portal and systemic circulation.⁴ It is the most common congenital hepatobiliary disorder in dogs and can manifest as either intrahepatic or extrahepatic, depending on breed. Intrahepatic shunts can be seen in medium- to large-breed dogs, with Irish wolfhounds and Labrador and golden retrievers predisposed, while extrahepatic is more common in terriers and smaller-breed dogs.⁴ Clinical signs can be seen in dogs less than 1 year of age.⁵ Extrahepatic shunts occur less frequently in cats; however, CPSSs have been described in mixed-breed cats, with increased prevalence in purebred Himalayans and Persians.⁵

Dogs with CPSSs have shunting of portal blood into systemic circulation, causing hepatic atrophy, and are often smaller than their littermates, with a failure to thrive. Common clinical signs may include anorexia, vomiting, diarrhea, constipation, ptyalism (more common in cats), polyuria/polydipsia, stranguria, and hematuria. Portosystemic shunting of blood increases circulating levels of toxins, such as ammonia originating from the intestinal tract, sensitizing neuronal tissues and leading to hepatic encephalopathy. Signs of abnormal neurologic function include ataxia, seizures, blindness, and head pressing, which can be triggered after ingesting protein-rich meals.⁶ The clinical signs Autumn was exhibiting were a result of toxin buildup because the liver was malfunctioning and not filtering waste material.

Common diagnostic tests include a CBC, serum biochemical profile specifically testing liver enzymes, urinalysis to detect ammonium biurate crystals, coagulation profile, and serum bile acid activity. Additional comprehensive testing can include an abdominal ultrasound, computed tomography, portography, magnetic resonance imaging, and exploratory surgery.

Medical management is required before undergoing surgery to reduce anesthetic and surgical complications. The goal is to reduce the amount of toxins produced in the gastrointestinal tract and the degree to which they are absorbed. Medical therapy consists of a low-protein diet and oral administration of antibiotics and lactulose to decrease ammonia-producing colonic flora.⁵ Although undocumented, the use of a supplement, such as SAMe, acts as a potent antioxidant and hepatoprotective agent.⁷ The decision to use LRS for fluid therapy in Autumn’s case was based on the veterinarian’s discretion. A study conducted has shown that LRS or acetated Ringer’s solution may be used in liver disease, as LRS contains both D- and L-lactate and is unlikely to increase blood lactate levels.⁸ To prevent muscle catabolism, dogs with a CPSS should receive enough protein in their diet either through a therapeutic diet or by replacing a meat-based diet with highly digestible vegetable and/or dairy proteins.⁹ If a dog responds well to an initial protein restriction, tofu or, if necessary, white-meat chicken can be added to their diet to achieve canine maintenance energy requirements.¹⁰ Autumn’s RER was calculated using the formula 30 × (body weight in kg) + 70. DER was based on a calculation for growing puppies 4 to 12 months of RER multiplied by a factor of 2.

Surgery provides the best chance for a long, healthy life in most dogs with extrahepatic shunts. Dogs have a longer median survival time of 152 months if an attenuation device, such as an ameroid constrictor, is placed, with less than 5% mortality rate.⁴ Up to 80% of patients can be expected to return to normal liver function.⁴ However, attenuation has been associated with causing complications such as hemorrhage, hypoglycemia, portal hypertension, and postattenuation neurologic signs that can occur up to 72 hours after surgery.⁷ Approximately 10% of patients will never return to normal liver function and will likely require lifetime management but are less severely clinically affected.⁴ The liver grows very quickly following successful surgery, regenerating in 2 to 3 weeks and receiving progressively more portal blood flow, resulting in complete closure of the shunt and resolving clinical signs.⁶ Significant improvements in bile acid results are associated with a good clinical response; however, in some animals there remains a mild to moderate increase in bile acids, possibly due to subclinical shunting or concurrent portal vein hypoplasia.⁷

Summary

Three days after surgery, Autumn’s owner brought her back in for vomiting and retching, with a decreased appetite. A brief physical exam was performed. She was bright, alert, and responsive, with a rectal temperature of 38 °C (100.4 °F); mucous membranes were pink and moist, with a capillary refill time of 1 to 2 seconds, and weight was 1.45 kg (3.2 lb). The incision was clean and dry, staples remained intact, and no redness or discharge was present. The vomiting was occurring after administration of the amoxicillin trihydrate/clavulanate potassium. The veterinarian recommended discontinuing the antibiotic only, and a maropitant citrate injection was given at 1 mg/kg SC.

Autumn returned in 2 weeks for staple removal and recovered well with no further complications. A repeat bile acids test was performed 2 months later, with postprandial results remaining elevated (TABLE 2). An internist was consulted at a referral hospital, and an ultrasound was recommended but was not scheduled. The owner was directed to continue feeding Autumn a protein-restricted diet with egg whites, tofu, and white-meat chicken mixed in with her current food, and to keep her on zonisamide, lactulose, and metronidazole as prescribed. No further updates were documented in Autumn’s record.