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This is Cassandra’s first pregnancy. At 39 weeks, she is about to deliver a beautiful baby girl. She is feeling awake and alert. Her blood pressure is normal. Cassandra’s delivery is uneventful and mother and baby both seem healthy. One day later, Cassandra’s blood pressure is elevated. The nurse tells her that she has protein in her urine. Many doctors come in to see her. She overhears them throwing around words like preeclampsia, HELLP syndrome, acute fatty liver disease of pregnancy, and atypical hemolytic uremia. In a private discussion, her doctor tells Cassandra that they suspect she has a very dangerous condition called pregnancy-associated atypical hemolytic uremic syndrome. She requires treatment immediately.
What is pregnancy-associated atypical hemolytic uremic syndrome?
Hemolytic uremic syndrome in pregnancy, or pregnancy-associated atypical hemolytic uremic syndrome (p-aHUS), is a rare but serious disorder affecting one out of every 25,000 pregnancies. In the general population, hemolytic uremic syndrome is associated with ingesting food or drink contaminated with the O157:H7 strain of E. coli. The condition is considered atypical when it is not associated with food poisoning. Overall, about 5-10% of patients experience atypical hemolytic uremic syndrome which can be caused by certain medications, infections, or genetic predispositions. Hemolytic uremic syndrome in pregnancy is considered atypical because it is not associated with the O157:H7 E. coli.
P-aHUS is a life-threatening condition, most likely to occur in the post-partum period (the days or weeks immediately following giving birth). Many patients suffer neurologic damage and kidney injury. Ultimately, many organs can fail as a result of this condition and many patients suffer from end stage renal disease (kidney failure). Unfortunately, P-aHUS is a challenge to diagnose because it resembles other conditions, like preeclampsia with HELLP syndrome or acute fatty liver of pregnancy, that may arise during this time.
How physicians can distinguish between p-aHUS, HELLP syndrome, and acute fatty liver of pregnancy
Some very important distinctions can be made between HELLP syndrome, acute fatty liver of pregnancy, and p-aHUS that can help physicians make an accurate diagnosis. First, as mentioned above, p-aHUS occurs in the post-partum period. Whereas, in contrast, both HELLP syndrome and acute fatty liver of pregnancy typically arise in the third trimester. A second important difference between p-aHUS and the other two conditions is that, unlike in p-aHUS, a woman will recover from both HELLP syndrome and acute fatty liver of pregnancy within about a week of delivery. Finally, when distinguishing between the three conditions, it is important for a physician to take into account primary clinical presentations—HELLP syndrome usually manifests as high blood pressure and protein in the urine, acute fatty liver of pregnancy usually causes nausea and vomiting, and p-aHUS has kidney involvement.
Pregnancy-associated hemolytic uremic syndrome
- Usually occurs in the days to weeks following giving birth
- No spontaneous recovery after giving birth
- Kidney involvement
- Usually arises in the third trimester
- Recovery within one week of delivery
- High blood pressure and protein in the urine
Acute fatty liver of pregnancy
- Usually arises in the third trimester
- Recovery within one day of delivery
- Nausea, vomiting, and fatigue
What causes hemolytic uremic syndrome?
As stated above, we typically see hemolytic uremic syndrome associated with ingestion of O157:H7 strain of E. coli. Atypical hemolytic uremic syndrome occurs in the absence of this bacteria. There may be a genetic predisposition to developing atypical hemolytic uremic syndrome.
In both typical and atypical hemolytic uremic syndrome, the condition comes about as a result of activation of the complement system. When normally functioning, the complement system enhances the immune response to our body’s outside invaders. In hemolytic uremic syndrome, the complement system is activated and then continues to operate uncontrolled. This leads to damage to the inside lining of the blood vessels (or the endothelium). In response to this endothelial damage, clots form in the blood vessels. This leads to hemolysis (rupture of red blood cells), low platelets, and kidney injury.
Is there any treatment?
At this time, the mainstay of treatment is plasmapheresis. Physicians also add on treatment with a monoclonal antibody called eculizumab which targets a component of the overactive complement system. It is hoped, in the future, that targeted gene therapy could one day be used to combat this deadly condition.