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A Medical Guide to House

Tuesday, November 28, 2006

A Simple Case of Vampirism

"Watson, if it should ever strike you that I am getting a little over-confident in my powers, or giving less pains to a case than it deserves, kindly whisper 'Norbury' in my ear, and I shall be infinitely obliged to you." - Sherlock Holmes, The Yellow Face
The patient: Alice is a 6-year-old girl who experiences problems with vision on a carnival ride and ends up in the hospital with abdominal pain, apparently due to pancreatitis. She has a low-grade fever and mild anemia. Her bile duct is dilated on a CT scan, indicative of stones in the bile duct (choledocholithiasis). The stones weren't visualized, so House states that the stones likely passed already and recommends an ultrasound to see if there are any stones left in the gallbladder. Gallstones are visualized in the gallbladder, and House recommends removal of the gallbladder to figure out what the cause is. After some court drama, the patient has her gallbladder removed (cholecystectomy). Following the surgery, Alice complains about pain from her stitches and Foreman notes a bright red vesicular rash with areas of denuded skin. She has no history of allergies. The stones are noted to contain calcium and bilirubin with a pigmented appearance. Because the patient presented with a low-grade fever and mild anemia, House suggests a bacterial infection. Foreman argues that bacterial infections do not cause a vesicular rash. House suggests a scratch test to rule out allergies. The scratch test is positive for all antigens. House is still convinced that the cause is bacterial and gives the patient a peanut butter sandwich to prove that she is not allergic to everything. House wants to start broad-spectrum antibiotics, but because of some more court drama, Cuddy is appointed guardian of the child and decides to give metronidazole instead. The patient becomes hypertensive and tachycardic. After she is stabilized, Alice's father takes her and leaves the hospital but returns promptly when the Alice becomes stiff. House suspects that the patient's babysitter gave her an aspirrin (leading to Reye's syndrome) and tells Cuddy to put the patient on charcoal hemoperfusion. In the middle of the procedure, Alice starts experiencing extreme pain and paralysis in her left hand. She starts to become hyperthermic and thrombocytopenic. The vesicular rash spreads to her left arm. Her fever increases to 103. House suggests that the patient may have varicella based on its appearance but this doesn't fit because the patient has paralysis and no itching. Cameron suggests Rocky Mountain Spotted Fever. House says to start the patient on chloramphenicol for Rocky Mountain Spotted Fever. The rash spreads throughout her arms and legs, so House diagnoses her with necrotizing fasciitis and recommends bilateral arm and leg amputation. As the patient is on the operating table, Chase has a realization that the patient may have erythropoetic protoporphyria and runs down to tell House. Someone calls the surgeon and the surgery is cancelled.

The diagnosis: Erythropoetic protoporphyria

Working backwards: When Chase made the diagnosis of erythropoetic protoporphyria, he did so working on the assumption that the patient's allergic tendencies could be attributed to light exposure. Based on the Harrison's textbook, the first two lab studies to check when a patient is sensitive to light is a plasma porphyrin (to rule out porphyrias) and an ANA/Ro/La (to rule out lupus and other similar autoimmune processes). Even though Chase didn't order either of these studies, it makes sense that he presumed that one of these two diseases was leading to the patient's symptoms once he made the connection to the light. Had he ordered the tests, he would have found increased levels of plasma porphyrin. Some of the common porphyrias are porphyria cutanea tarda (#1), erythropotoetic protoporphyria (#2), and acute intermittent porphyria. If you tested the urine for porphyrins, porphyria cutanea tarda would show a normal porphobilinogen level and an increased uroporphyrin and 7-carboxylate level; erythropoetic protoporphyria would show normal porphyrin and porphyrin precursor levels; and acute intermittent porphyria would show increased levels of porphobilinogen.

Loose ends:
Q: If the disease is genetic, why don't either of Alice's parents show symptoms of the disease?
A: The disease is autosomal dominant, which means that even one copy of the gene should give you symptoms. However, some people with only one copy of the gene have been noted to have no symptoms, so there is a documented variation in the severity of the disease.

Q: Why was a diagnosis of pancreatitis thrown around early in the episode after the patient presented with abdominal pain?

A: Generally, when a doctor says that a patient likely has pancreatitis, he or she does so based on a blood sample that shows increased levels of amylase and lipase. Because pancreases make amylase and lipase to help digest food, damage to the pancreas breaks down individual pancreatic cells and releases these enzymes into the bloodstream, thereby elevating their levels in the blood. A CT scan could then be performed 48 hours after the onset of symptoms, with the goal to try to visualize some kind of fluid or cyst in the pancreas. I'm assuming then that this diagnosis was made because Alice was experiencing excruciating abdominal pain and had increased levels of amylase and lipase. Erythropoetic protoporphyrias are actually associated with gallstones (composed of insoluble crystalline protoporphyrin), which could have lodged in the common bile duct (like the one in the picture), creating a blockage of the main pancreatic duct and increasing the risk for pancreatitis.

Q: When Alice first developed a rash on her arm, why was it attributed to thrombocytopenia?

A: Thrombocytopenia is a low level of platelets, which can result in a petechial rash. From way up in the surgery viewing booth, it's possible that the patient's rash looked petechial in nature (like in the picture). I can't really think of a better explanation because I don't think a blood test was every run to confirm or reject this idea. Petechiae generally appear as small little dots.

Q: What things besides pancreatitis (and other anatomical diseases like appendicitis) can lead to abdominal pain, like the kind that Alice had?
A: There's a mnemonic I use from the Saint-Frances Guide to Inpatient Medicine to remember all the non-typical causes of abdominal pain.
Puking My BAD LUNCH.

Mediterranean fever

Black widow spider bite
Addison's disease, Angioedema
Diabetic ketoacidosis

Lead toxicity
Calcium high
Herpes Zoster

Q: Did vampires suffer from porphyria?
A: There is some thought that legends of vampires were based off of people who suffered from porphyria. Porphyria causes severe rashes when a person is exposed to sunlight, and one way to treat porphyrias is to transfuse blood products. Centuries ago when blood products weren't readily available, it would be theoretically possible to receive blood by drinking it straight from a victim's neck veins. Here's an interesting article that goes more into depth on the topic.


Blogger : : c a k e t a k e r : : said...

Commenting was turned off in your most recent post, so I'll post the comment here :)

Hurray~! You updated! Thanks so much for taking the time to write in this blog, I find it all so fascinating! I've been lurking on here for a while now.

Good luck on your medical studies!

7:19 AM  
Blogger k-deep said...

Thanks for the kind words. I had been lost in the grips of my surgery rotation, so I had tuned out for a bit.

7:48 PM  
Anonymous Anonymous said...

What I want to know is, why would they come up with EPP if it is not associated with abdominal pain and paralysis. It would more likely be VP or HCP, which do present with those symptoms, plus the photosensitivity. Who on the research team went on vacation for that episode?

3:35 PM  
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12:27 PM  
Anonymous Anonymous said...

great post. I would love to follow you on twitter.

12:31 PM  
Anonymous Anonymous said...

This has been on my mind for some time..... It does lead to other issues...

1:04 AM  

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