Hepatic Encephalopathy Secondary to Non-cirrhotic Portosystemic Shunt

Abstract

Hepatic encephalopathy is uncommon in the absence of cirrhosis. We report a 71-year-old woman who presented with altered mental status in the setting of hyperammonemia for the second time in 6 months. Magnetic resonance imaging of the abdomen revealed an uncommon portosystemic shunt involving an enlarged posterior branch of the right portal vein and an accessory right hepatic vein, with no features of cirrhosis. Appropriate management of these patients with ammonia-lowering therapy can reduce repeat episodes and improve quality of life. This case demonstrates the importance of diagnosing non-cirrhotic hepatic encephalopathy in patients with altered mental status.

Introduction

Non-cirrhotic portosystemic shunt formation is a rare condition that may go undetected due to its resemblance to hyperammonemia-associated hepatic encephalopathy (HE) due to cirrhosis, particularly in patients who lack the typical symptoms and physical signs of cirrhosis. The formation of portosystemic shunts leads to hyperammonemia with associated recurrent episodes of encephalopathy marked by dysarthria, ataxia, altered mental status, and personality changes. These patients are frequently misdiagnosed with psychiatric disorders or dementia, resulting in suboptimal treatment and a negative impact on their quality of life. ¹

The diagnosis can be established by identifying the evidence of portosystemic shunting on abdominal imaging such as computed tomography (CT) or magnetic resonance imaging (MRI), regardless of the presence of liver disease. ² Early diagnosis is crucial because interventional radiology procedures can offer a potential cure. ³ Herein, we present a patient diagnosed with HE in the absence of cirrhosis. The HE was due to a portosystemic shunt involving an enlarged posterior branch of the right portal vein and an accessory right hepatic vein.

Case Presentation

A 71-year-old Hispanic woman with a history of hypothyroidism and hypertension presented to the emergency department with recurrent episodes of confusion, weakness, and difficulty with ambulation. She was suspected to have cirrhosis during her previous hospital admission, but she did not follow up as an outpatient to confirm the diagnosis, determine etiology, or manage her symptoms. Physical examination revealed an alert female who was ataxic and oriented only to herself. Total bilirubin was 0.7 mg/dL, alkaline phosphatase 97 IU/L, aspartate aminotransferase 35 IU/L, alanine aminotransferase 29 IU/L, albumin 4.1 g/dL, platelets 207 × 10³/µL, and International Normalized Ratio (INR) 1.1. An ammonia level of 86.7 µmol/L was the only significant laboratory result. Laboratory work was also done to evaluate possible causes of cirrhosis. The patient’s ceruloplasmin was normal and hepatitis panel, antimitochondrial antibody, alpha-1 antitrypsin, and HIV testing were negative. Anti-smooth muscle antibody (ASMA) was positive at 33 U. A CT angiography of the head revealed diffuse cerebral volume loss with associated intracranial atherosclerosis and chronic microangiopathic white matter changes.

An ultrasound of the abdomen revealed no definitive sonographic features of cirrhosis. A chart review of the prior admission was done to clarify the reported history of cirrhosis, revealing a portosystemic shunt seen on a CT scan. (Figure 1) A new MRI of the abdomen with contrast confirmed the stable portosystemic shunt. The patient’s symptoms improved quickly with lactulose and rifaximin treatment, and she was discharged with plans for interventional radiology embolization of the shunt. However, the patient was lost to follow-up.

Figure 1.

Intrahepatic portal venous shunt.

Discussion

Our patient presented with an overt episode of HE per West Haven criteria secondary to a portosystemic shunt. ⁴ Hepatic encephalopathy can be caused by chronic liver disease with portosystemic shunting or by shunting without cirrhosis. However, the latter is a rare cause of HE, and its diagnosis can be challenging. In this case, our patient experienced several episodes of HE, but no definitive clinical, radiographic, or laboratory evidence for chronic liver disease was found. Interestingly, she was positive for ASMA, but serum positivity for autoimmune markers, without other significant clinical evidence for chronic liver disease, is nonspecific. ⁵ Thus, it was concluded that the portosystemic shunt was the cause of the recurrent episodes of HE.

Portosystemic shunting can be classified into several categories based on the anatomic location of the shunt. ² Our patient had a type 1 shunt, which was intrahepatic, between the right portal vein and an accessory right hepatic vein. Other subtypes include type 2, which is an intrahepatic and extrahepatic shunt; type 3, which is an extrahepatic bridge involving the left gastric vein, splenic vein, or superior mesenteric vein, and terminating at the left renal vein or inferior vena cava; type 4, which is similar to type 3 but with the added feature of idiopathic portal hypertension; and type 5, which is defined by the congenital absence of the portal vein. ²

The causes of these shunts are not well understood, but they range from being congenital to being iatrogenic/trauma-induced or related to cirrhosis or idiopathic portal hypertension. ² As our patient had no history of trauma or cirrhosis, it was suspected that she had a congenital malformation that became apparent later in life. Shunts can increase in size over a patient’s lifespan and become symptomatic, explaining why the incidents of shunts are greatest in the elderly.^2,6

Clinical complications of congenital shunts vary depending on the type and size of the shunt and can affect multiple organ systems. The most common complications are neurologic, as in our patient’s case, with symptoms that include lethargy, confusion, behavioral changes, disordered sleep, or even coma. ⁷ Hepatic laboratory abnormalities associated with portosystemic shunts include hyperammonemia, hyperbilirubinemia, and elevated liver enzymes, while cardiopulmonary manifestations include portopulmonary hypertension, hepatopulmonary syndrome, and even heart failure secondary to cardiomyopathy. ⁷

Our patient was treated with lactulose to reduce ammonia production levels through acidification of the colon, which is standard for HE. ⁴ Rifaximin was added as it has shown to be efficacious in conjunction with lactulose therapy. ⁸ For definitive management, our patient was referred to interventional radiology for embolization of the shunt. Embolization of the portosystemic shunt is a safe and effective management strategy for patients who have medically refractory HE. ⁹

In conclusion, this case is a rare example of a presumed congenital anomaly causing HE through the shunting of portal blood to the systemic circulation. A thorough history, laboratory testing, and radiographic workup for patients who demonstrate HE are recommended to reach a definitive diagnosis and proper management.