Primary biliary cholangitis (PBC) is an autoimmune disease that damages the bile ducts inside and outside of the liver. The damage is caused by immune cells that attack the bile duct cells and prevent them from working normally. PBC occurs most commonly in middle-aged to elderly women, with over 90% of patients being female. It tends to have a gradual onset with symptoms including itchy skin, fatigue, and yellow skin. Blood work often detects antimitochondrial antibody (AMA) and an increase in liver enzymes called alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT).
The liver is an organ found in the right upper part of your abdominal cavity. It is responsible for removing toxins, processing medications, and producing substances such as bile that are essential for breaking down and using food.
The liver contains multiple types of cells which make up its structure and contribute to function. The main type of cell in the liver is called a hepatocyte. The liver also has biliary cells which line the inside of long channels called bile ducts, and endothelial cells which line the inside of blood vessels. There are also a variety of background cells and materials that support and hold all these other parts of the liver together. Liver disease can affect any of these cells which can lead to damage and loss of the cells over time.
There are several complications of primary biliary cholangitis (PBC). One important complication is liver cirrhosis, which usually occurs 10-15 years after diagnosis. When this occurs, patients may require a liver transplant. PBC also increases the risk of cholangiocarcinoma (cancer of the bile ducts).
A liver biopsy is performed in primary biliary cholangitis mainly to determine the number of ducts that have disappeared due to damage, and the amount of fibrosis (scarring) within the liver. When examining your tissue sample under the microscope, your pathologist will look for several important microscopic features before diagnosing you with PBC. These features are described in greater detail in the sections below.
The liver produces a substance called bile which is used to remove toxins from the body and digest food. The bile produced in the liver drains through channels called bile ducts into the small bowel. Each portal tract contains one bile duct. Your pathologist will look for bile duct damage or active inflammation around the bile ducts.
In primary biliary cholangitis, the classic microscopic finding is a type of bile duct injury called a “florid duct lesion”. In this type of injury, the bile ducts are attacked by multiple types of cells from the immune system. The bile ducts look disrupted, and the cells in them can appear swollen. The number of inflammatory cells which are attacking the bile duct often results in an increase in the size of the portal tracts as well.
If damage or inflammation continues for a prolonged period of time, the injured bile ducts may be lost. Your pathologist may record the amount of bile duct loss in multiple ways including stating the actual number lost, the percentage lost, or the degree of loss (mild, moderate, or severe). When there are decreased numbers of bile ducts this may be stated as ductopenia.
A granuloma is a special type of inflammatory response where cells from the immune system work together to surround a target. The portal tracts in PBC often contain granulomas in areas where bile ducts have been damaged. Your pathologist will report them if they are present.
Cholestasis is a word pathologists use to describe bile trapped in the liver. Trapped bile is important because it can cause liver injury. If cholestasis is seen, your pathologist will describe its location within the liver and the amount of trapped bile will be described as mild, moderate, or severe. Because primary biliary cholangitis damages the bile ducts, there is often cholestasis present in the liver biopsy.
Fibrosis is a type of scar tissue that forms in the liver after damage. Because PBC damages the liver, there is a risk of developing fibrosis. Most pathology reports comment on the amount of fibrosis and will assign it a ‘stage’. The stage is dependent on multiple factors including extent of initial injury, the length of time injury was occurring, and which parts of the liver were damaged. Too much fibrosis disrupts the architecture of the liver and prevents it from functioning properly.
There are several different classifications systems used to stage fibrosis but all of them include the type and amount of fibrosis seen. Cirrhosis is the last stage of fibrosis and it is characterized by large fibrous bands in the liver. In diseases that affect the bile ducts (such as PBC), the fibrosis may be patchy and irregular. Fibrosis prevents the liver from carrying out its normal functions and may lead to a medical condition called ‘liver failure’.
The liver is divided into ‘zones’ and at the center of each zone is a structure called a ‘portal tract’. Portal tracts are important because they contain blood vessels and channels that move other substances such as bile in and out of the liver.
When examining a liver biopsy, your pathologist must first determine if the sample contains the minimum amount of portal tracts required to make an accurate diagnosis. The adequacy of the biopsy may be reported simply as “yes” or “no”, or the number of portal tracts seen may be stated.
The condition of the liver biopsy when viewed under the microscope is usually described. If the liver biopsy is brittle and has broken apart this will be described, as it may be a clue to specific liver conditions.
Steatosis is the term used to describe the presence of fat droplets within the hepatocytes. In steatosis, the hepatocytes contain clear areas of fat droplets when viewed under a microscope.
Pathologists use a scale to describe the amount of fat in a liver with steatosis. The scale is based on the percentage of liver cells that contain fat droplets:
The scale used by most pathologists includes:
Ballooning hepatocytes are liver cells that are damaged or dying. The hepatocyte swells to several times its normal size and becomes clear in areas. Ballooning hepatocytes are required for the diagnosis of several medical liver diseases. The amount of hepatocyte ballooning present is reported as mild, moderate, or severe.
Mallory bodies form because of damage to hepatocytes. Under the microscope, they look like dark pink material inside of the cells. Mallory bodies are present in specific forms of liver disease and their presence or absence helps guide pathologists to a diagnosis.
Iron can build up within the liver as a result of the abnormal breakdown of iron, increased iron in the body (such as after multiple blood transfusions), or when the liver is not functioning properly (as in liver cirrhosis). This excess iron can be seen within the hepatocytes or within immune cells called macrophages. If iron is present in your tissue, your pathologist will report its location and severity.