Wednesday, October 10, 2007

Housewatch - Episode 4.3

Another episode of House, another post. This time, the patient had the misfortune to suffer from spinal muscle atrophy. In his case, it was ascending, which means it started at his feet, and slowly worked its way up his body. Like last week's disease, it's genetic. But SMA is recessive, which means you need two copies of the bad gene, instead of just one, as in von Hippel-Lindau.

SMA kills motoneurons, which are the nerve cells that control muscles. Related diseases include amyotrophic lateral sclerosis, aka Lou Gehrig's Disease, and Parkinson's. In SMA, the mutated gene (SMN1, or survival motor neuron 1) makes a protein that is essential for nerve cell maintenance. Without it, the nerve cells shrink and die, and without stimulation, the muscles atrophy.

They called what actually killed him by two names, threadworm and Strongyloides. This was very confusing, since they are different, but related diseases. Both are caused by a worm infection. In each case, the 1-cm worms can easily be seen in the stool. That's why the male team wanted a stool sample.

Threadworm, or pinworm, is a very common illness. As this article notes, one course of treatment is usually sufficient to cure the disease. (The patient did not have this.)

Ickiness from Wikipedia:


Pinworm eggs are easily seen under the microscope.
Pinworm eggs are easily seen under the microscope.

After mating, the male dies. The female migrates to the anus and emerges, usually during the night, to deposit about 10,000 to 20,000 eggs in the perianal area (around the anus). She then secretes a substance that causes a very strong itching sensation, inciting the host to scratch the area and thus transfer some of the eggs to the fingers. Eggs can also be transferred to cloth, toys and the bathtub. Once ingested orally, the larvae hatch and migrate back to the intestine, growing to maturity in 30-45 days. The eggs can survive from 2 to 3 weeks on their own outside of the human body. It is also in some cases where the larva will hatch around the skin of the anus and travel back inside the anus, up the rectum and back into the intestines where it matures. (SOURCES: Rudolph's Pediatrics - 21st Ed. 2003; Current Medical Diagnosis & Treatment - 45th Ed. 2006)

The patient actually had Strongyloides, which involves a different worm that can infect dogs and be transmitted between humans and dogs. This article is very informative. Like a lot of parasites, it has a bizarre life cycle.

But it's easy to treat with a dose or two of ivermectin, which is why everybody was upset at the end that it wasn't caught. Or that it was caught, and the medicine wasn't delivered.

And what about the dog? The dog died because it ate the ivermectin pills intended for the patient. Collies react unusually to it (J Vet Intern Med. 2002 Jan-Feb;16(1):89-94. Ivermectin toxicity in 17 collies. Hopper K, Aldrich J, Haskins SC.).

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