Primary biliary cirrhosis
AssessmentsPrimary biliary cirrhosis
Primary biliary cirrhosis
USMLE® Step 1 style questions USMLE
A 44-year-old female comes to her primary care provider due to fatigue and intense pruritus for the last 2 months. She works as a schoolteacher and has felt excessive daytime somnolence that is interfering with her job. Past medical history is significant for chronic autoimmune (Hashimoto) thyroiditis, for which she has been taking daily levothyroxine. She drinks 1-2 glasses of wine on the weekends and denies smoking tobacco or using illicit substances. Her temperature is 37.2°C (99.0°F), pulse is 82/min, respirations are 12/min, and blood pressure is 128/82 mmHg. Physical examination reveals multiple excoriations on her trunk and extremities. The liver is palpated 4 cm below the costal margin and is not tender to palpation. Laboratory results are as follows:
Which of the following complications is associated with this patient’s disease process?
Primary biliary cirrhosis exam links
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Primary biliary cholangitis and cirrhosis, or PBC, is an autoimmune disease where the T cells attack the cells that line the smaller-sized bile ducts in the liver.
As the cells are damaged or destroyed by immune attack, they start letting bile leak through their tight junctions and into the interstitial space, where it can get into the blood and the other liver cells.
This can cause inflammation and symptoms that are similar to cholestasis and obstructive jaundice, both of which there’s some disturbance in bile flow.
At first it presents as chronic inflammation, which is where it gets the name cholang-itis, for inflammation of the bile ducts, but advanced stages of the disease leads to cirrhosis as more cells are destroyed both from the autoimmune attack and infiltration of bile.
As with a lot of autoimmune diseases, the exact reason why T-cells start attacking these bile duct cells is unknown, and it’s likely related to genetic predisposition in combination with environmental triggers, and is associated with other autoimmune diseases like autoimmune hepatitis and Sjogren’s syndrome.
PBC tends to affect women at a much higher rate than men, about a 9:1 female to male ratio.
For some reason that has yet to be completely figured out, in almost all cases of PBC, your body creates antibodies to mitochondria, specifically a mitochondrial protein called PDC-E2; for that reason, one of the most notable markers in PBC are these antibodies to mitochondrial proteins (or AMAs) in the patient’s blood, as many as 95% of patients with PBC have AMAs in their blood.
Why though, are the bile duct cells specifically targeted? Don’t all cells have mitochondria? Shouldn’t these AMA’s be targeting all cells then?
One theory is based on a concept called molecular mimicry, where the antigens that bring about this autoimmune response are really similar to another protein, but different enough so that the immune system gets confused and thinks it’s a foreign version of that particular protein.
Here’s an example of two people’s cells, they both have this triangle protein, but they have different colored triangles, each person’s immune knows that these are their own proteins, their own self-proteins and that they shouldn’t attack, but they have antibodies for proteins that are very similar, but definitely different from self, so say they have antibodies for triangles, just different colored triangles, so like person A has red, yellow, and blue, just not green, and person B has green, yellow, and blue, and not red. So both these people’s immune systems are like yep, these are all self so we’re good.
But now say person B’s red triangle turns into a green triangle instead, the immune system’s like...huh, weird, that’s not red, that must not be ours, and so the green triangle antibody binds it and the immune system kicks in, destroys the cell, and starts making a ton of these matched antibodies.
So similarly with PBC, you’ve got these AMAs for foreign versions of the PDC-E2 protein in your mitochondria, so like maybe yours is a red triangle, so you don’t have antibodies to red triangle PDC-E2 because your immune system knows that red equals self.
So the theory is, and mind you this is most definitely a theory, on why patients with PBC have a ton of these AMAs in their blood for PDC-E2 is that some infection or maybe a chemical in the bile ducts, an environmental trigger of some kind, damages a bile duct cell in such a way that now it shows a protein that happens to be really similar to PDC-E2 in structure, so it’s a triangle, but it’s different enough to be non-self, so maybe it’s green in color instead of red; and this triggers an immune response to this particular green-triangle protein, which is similar but not the same as the red-triangle protein in the mitochondria, and so the immune system starts pumping out these green-triangle anti- mitochondrial antibodies or AMAs, even though the target antigen isn’t even necessarily from the mitochondria, it’s just sort of mimicking the structure of the mitochondrial protein! Wild eh? That’s the theory, anyway, and sort of helps explain why just the bile duct cells are being attacked, and not all cells.
Primary biliary cirrhosis (PBC), also referred to as primary biliary cholangitis, is a chronic autoimmune disease that affects the liver. It is characterized by the progressive destruction of the small bile ducts in the liver, which leads to inflammation, fibrosis, and ultimately cirrhosis (scarring) of the liver. Symptoms may not appear until the later stages of the disease but can include fatigue, itching, jaundice, and abdominal pain. Treatment involves drugs like ursodeoxycholic acid (UDCA) and cholestyramine, which slow the progression of the disease and improve symptoms. In advanced cases, liver transplantation may be necessary.
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