One of the pathologies that can affect the biliary system of dogs is cholestasis. This alteration consists of the abnormal accumulation of bile in the liver, bile ducts or gallbladder that occurs as a result of a blockage or suppression of bile flow. Determining the specific cause of cholestasis will allow it to be classified and the most appropriate treatment to be established in each case.
What is cholestasis in dogs?
Cholestasis is defined as the abnormal accumulation of bile in the liver, bile ducts, or gallbladder This accumulation of Bile is produced by the existence of a blockage or suppression of the bile flow, which totally or partially prevents the arrival of bile to the intestine.
To better understand how cholestasis occurs, we will briefly explain its pathogenesis. The hepatocytes are the parenchymal cells of the liver that carry out most of the functions of this organAmong other things, hepatocytes are responsible for producing the components of bile and secreting them into the bile canaliculus (the space between two adjacent hepatocytes). Once in the canaliculus, the bile passes into the intrahepatic bile ducts (that is, those within the liver itself), then into the extrahepatic bile ducts, and finally into the gallbladder where it is stored. When the dog eats a meal with protein and fat, the contraction of the gallbladder occurs and bile flows into the small intestine, which allows proper digestion and absorption of fat. When, due to an intra or extrahepatic cause, bile does not flow correctly through the bile ducts, cholestasis occurs.
When cholestasis is maintained over time, hepatocytes end up being injured, since the bile acids present in the bile have a detergent action on the cell wall of hepatocytes.
Types of cholestasis in dogs
Depending on the cause of the abnormal accumulation of bile in the liver, cholestasis is classified into two types:
- Intrahepatic cholestasis: when the cause of cholestasis is found in the liver itself and affects the intrahepatic bile ducts.
- Extrahepatic cholestasis: when the cause of cholestasis is outside the liver, affecting the extrahepatic bile ducts.
In the following section, we explain the different causes that can cause intrahepatic and extrahepatic cholestasis in dogs.
Causes of cholestasis in dogs
As we have explained, the causes of cholestasis vary depending on whether it is intrahepatic or extrahepatic cholestasis.
Intrahepatic cholestasis
The main causes of intrahepatic cholestasis in dogs are:
- Intrahepatic bile duct obstruction: due to parasites, thick bile syndrome, inflammation of the bile ducts (cholangitis) or tumors of the bile ducts (cholangiocarcinoma).
- Inflammation or fibrosis at the level of the portal space: the portal spaces are tubular structures that cross the liver. Through them pass blood vessels, lymphatic vessels and bile ducts. When these spaces become inflamed or fibrotic, they compress the structures inside them, including the lymphatic vessels.
Extrahepatic cholestasis
Extrahepatic cholestasis occurs when there is an obstruction at the level of the extrahepatic bile ducts or at the level of the gallbladder. In turn, this obstruction can be caused by:
- Gallstones, parasites, or clots that obstruct the lumen of the extrahepatic bile ducts.
- Thick bile syndrome: when the bile is so thick that it doesn't flow properly and blocks the bile ducts.
- Tumors (cholangiocarcinoma) or inflammatory processes (cholangitis) that affect the wall of the bile ducts.
- External compression of the bile ducts: due to pancreatitis or lymphadenitis of the portal or mesenteric nodes. When these organs increase in size, they can compress the bile ducts from the outside and obstruct them.
Symptoms of cholestasis in dogs
The main sign of cholestasis is jaundice, which consists of a yellowish coloration that is observed at the level of the skin and mucous membranes as a result of bilirubin deposition. Usually, bilirubin is excreted through the bile, however, in the case of cholestasis, this pigment accumulates in the liver and passes into the blood, producing hyperbilirubinemia (increased levels of bilirubin in the blood). When bilirubin levels in the blood are higher than 2 mg/dl, it is deposited in the tissues, giving rise to jaundice. In dogs, jaundice is more easily observed at the level of the sclera, although it can also be seen in the oral mucosa, genital mucosa and even in the skin when bilirubin levels are very high.
In addition to jaundice, when total obstruction of the bile ducts occurs, the following clinical signs may be observed:
- Maldigestion/malabsorption syndrome: the bile s alts present in the bile are essential for the digestion and absorption of fats. When the bile is unable to reach the intestine, a maldigestion/malabsorption syndrome appears, characterized by the appearance of osmotic-type diarrhea.
- Steatorrhea: consists of the presence of fat in the stool. When the bile s alts do not reach the intestine, the fats are not digested or absorbed, so they are eliminated with the feces.
- Faeces without color (acholic): the color of the feces is due to the presence of stercobilinogen, a metabolite obtained from the bilirubin. In cases of cholestasis, the bilirubin contained in the bile does not reach the intestine, which means that stercobilinogen is not produced and the stool is colorless.
- Bleeding tendency: During cholestasis, malabsorption of vitamin K occurs. Deficiency of this vitamin can lead to alterations in secondary hemostasis, increasing the tendency to bleed.
- Bacterial Cholangitis: When the obstruction is complete, bacteria from the intestine can ascend the bile duct and colonize the bile ducts, causing a bacterial cholangitis.
When there is an extrahepatic obstruction that persists over time, the bile ducts or the gallbladder itself can rupture. When the bile falls into the abdominal cavity, it generates a peritonitis that can be septic or aseptic, depending on whether or not bacterial contamination occurs.
Diagnosis of cholestasis in dogs
Once we have described the main causes and symptoms associated with cholestasis, we will explain its diagnosis.
Specifically, the diagnostic protocol for cholestasis in dogs should be based on the following points:
- Medical history and physical examination: As we have detailed in the previous section, dogs with cholestasis usually present jaundice, although they can also watch for digestive signs (diarrhea, steatorrhea, and discolored stools), as well as abdominal pain.
- Blood analysis with liver profile: the most characteristic feature of cholestasis is the increase in two liver enzymes, alkaline phosphatase and GGT (gamma-glutamyl transpeptidase). The increase in these enzymes occurs prior to the onset of jaundice. In addition, an increase in the levels of bilirubin in the blood can be observed.
- Abdominal ultrasound: When there is a blockage of the bile ducts, bile cannot reach the intestine, so it accumulates in the bile ducts. As a consequence, there is a dilation of the bile ducts and/or the gallbladder that can be visualized by ultrasound. However, the gallbladder may simply be dilated due to anorexia (because if the animal does not eat, the stimulus for its emptying is not produced). Therefore, to diagnose an obstruction of the bile ducts, it is necessary to visualize not only the dilatation, but also the obstructive cause. In cases of gallbladder rupture, a poorly defined gallbladder area and the presence of free fluid in the abdomen can be seen.
- MRI: This advanced imaging test can help detect the presence of an obstruction at the level of the extrahepatic biliary tract.
- Exploratory laparotomy: when the ultrasound reveals dilation of the bile ducts, but the cause of the obstruction is not observed, exploratory surgery of the abdominal cavity may be necessary to make the causal diagnosis.
Treatment for cholestasis in dogs
The treatment of cholestasis in dogs should be directed at the cause that produces it, and may include medical treatment, surgical treatment or both of them.
Medical treatment
Medical treatment will vary depending on the cause of cholestasis, and may be administered hepatoprotectors (such as ursodeoxycholic acid or silymarin),antibiotics, vitamin supplements (including vitamin K, E or D),fluid therapy when there is dehydration, etc. In addition, it is important to restrict the fat content of the diet until normal bile flow to the intestine is restored. Thus, foods that are prohibited in dogs with cholestasis are those that are high in fat.
Surgical treatment
Surgical treatment is often necessary when cholestasis is caused by extrahepatic obstruction. Surgical options may include:
- The Gallbladder removal (cholecystectomy), since a dog without a gallbladder can still have a good quality of life.
- The opening of the gallbladder or bile duct to remove stones, clots, or other things that block the bile duct.
- Placing bile duct stents to keep them open to the passage of bile.
- Removal of tumors that externally compress the bile ducts.
As we can see, there is no natural treatment for cholestasis in dogs, beyond changing the diet, so it is necessary to go to the veterinary clinic to obtain a diagnosis and adequate treatment.
