Monday, June 29, 2009

Case of the Week 75

A patient who recently returned from the Philippines presented with recurrent fevers, chills, and sweating. A peripheral blood smear showed the following (Giemsa stain, 1000x original magnification, oil immersion). Identification?

Sunday, June 28, 2009

Answer to Case 75

Answer: Plasmodium ovale
This was a somewhat difficult case, in that you had to differentiate this species of malaria-causing parasite from the similar appearing and closely related species P. vivax. With both infections, the parasites invade young RBCs, so the infected cells are enlarged compared to the neighboring RBCs, and prominent cytoplasmic stippling is present. The difference lies mostly in the chromatin pattern. In P. vivax, the chromatin is referred to as "ameboid" (also spelled amoeboid). In contrast, the chromatin of P. ovale is less ameboid, and typically more compact. RBCs infected with P. ovale also classically have an oval shape, with a jagged or fimbriated edge, although this is less reliable. Finally, the schizonts of P. vivax contain 12-24 merozoites, whereas the schizonts of P. ovale contain only 6-12 merozoites. The images below demonstrate some of these key differences.

P. ovale

P. vivax

Lastly, the travel history of the patient is important in confirming the morphologic diagnosis. This patient had traveled to the Philippines, which is known to be endemic for P. ovale. This species is also found in Sub Saharan Africa, New Guinea, and parts of SE Asia.

Monday, June 22, 2009

Case of the Week 74

The following helminth is a rare intestinal pathogen of humans. It embeds its spiny proboscis into the mucosa of the small intestinal, typically causing severe cramping and abdominal pain. Other symptoms include fever, nausea, vomiting, anorexia, weight loss, diarrhea, constipation or bloody stools. The morphology of the adult worm is classic:

20x original magnification

40x original magnification

100x original magnification

Identification? (note - only the general category of organism is necessary).
How is infection with this organism typically acquired?

Sunday, June 21, 2009

Answer to Case 74

Answer: acanthocephales (thorny-headed worms)/phylum Acanthocephala
Congratulations to "Anonymous" and Alasdair who got this correct right away. In the words of Alasdair "Acanthocephales, and such a beautiful parasite (if I may say so!)".

It definitely is a striking appearing parasite, as the thorny head is quite apparent.

Acanthocephala are parasites of fish, as Alasdair mentioned, but they are also parasites of other vertebrates, including pigs, rats, and (rarely), humans. The most common ones to parasitize humans are Moniliformis moniliformis and Macracanthorhynchus birudinaceus.

Humans acquire this infection through ingestion of various beetles and cockroaches which are the intermediate host for these parasites.

Thanks for writing in with your comments!

Monday, June 15, 2009

Case of the Week 73

The following worm was an incidental finding during routine screening colonoscopy in a patient from the Philippines. It measures approximately 4 cm in length, and was mounted on a slide for better visualization of its internal structures.

BONUS: Which end is anterior and which is posterior?

Sunday, June 14, 2009

Answer to Case 73

Answer: Trichuris trichiura, otherwise known as the "whipworm" due to its whip-like shape. Notice that this example is a gravid female, with clearly identifiable eggs inside the uterus. Congratulations to all of the viewers who wrote in - either on the blog or via email.

The second part of the question was a bit tricky, but DrJ got it correct:
"the whip is the anterior end, which seems backwards to me because I always thought of it as a tail." Most people get this wrong, since they tend to think of a worm body decreasing in diameter rather than increasing. However, it makes sense if you understand the life cycle of the adult female. The head is threaded into the mucosa of the large intestine, allowing the worm to feed on tissue secretions (best accomplished with a narrow anterior end). The posterior end is larger because it contains the gravid uterus, packed full of eggs. The adult female produces 2,000-20,000 eggs daily! Note that the posterior opening is wide enough to easily accommodate the release of these eggs. The images below nicely illustrate the anterior and posterior ends:

Finally, to answer one of the comments I received: I pronounce Trichuris: Try-cure-us (although I was trained in London so I tend to lean towards British pronunciations).

Sunday, June 7, 2009

Case of the Week 72

This weeks Case is a bit more straight-forward:

The following object was identified in the diaper of an infant by his mother. It measures approximately 6 mm in length, and was white and motile. Shown here is the object mounted on a slide and stained with carmine (2x objective; 20 times original magnification.

(10x objective; 100 times original magnification)

Saturday, June 6, 2009

Answer to Case 72

Answer: This is a classic example of a Dipylidium caninum proglottid. Note the pores on either side of the proglottid (hence the name "double-pored dog tapeworm). Within the proglottid, you can observe numerous immature egg packets. These are highlighted below, with the inset showing the appearance of an immature egg packet that was expressed from a proglottid in a separate case. Note that the eggs contain refractile hooklets, like those seen in some other cestode eggs such as Taenia spp. and Hymenolepis spp. If you see hooklets in an egg, that's a sure sign that you are dealing with a cestode egg.

The history is also classic for infection with this cestode. Children and institutionalized adults are the most typically infected hosts, since infection is acquired through ingestion of an infected dog or cat flea.

Treatment with praziquantel is simple and effective in most cases. The Medical Letter provides an excellent discussion of treatment options.

Monday, June 1, 2009

Case of the Week 71

The following is a section of a large invasive liver mass from a farmer and hunter in the Midwestern U.S. He reports no travel history outside of the U.S.


Answer to Case 71

Answer: Echinococcus multilocularis

This is a difficult case, especially for those that are not used to looking at tissue sections. The history of a rapidly growing liver mass helps in formulating a differential diagnosis, and as one of the readers pointed out, Entamoeba histolytica must also be considered. The lack of travel history outside of the U.S. helps to exclude E. histolytica amebic liver abscess. The fact the patient is an outdoorsman is consistent with potential exposure to the natural hosts of this parasite: foxes and rodents. Infection with E. multilocularis, otherwise known as alveolar hydatid disease, is spreading throughout the American Midwest, and is also endemic in parts of Europe.

The diagnostic features of this case include the cystic nature of the lesion, the cellular septae (walls separating the cysts), calcaneous bodies/corpuscles, and hooked protoscoleces within the cysts. These features are pointed out on the images below:

The calcaneous corpuscles are very helpful in identifying cestodes in tissue sections, since both adults and intermediate forms have them. They simply represent non-specific calcified material, and can be seen in sections of Taenia solium cysticercosis and sparganosis, in addition to Echinococcus spp.

An important differential in this case is Echinococcus granulosus, since this species typcially causes more benign disease. While the two closely related species may cause similar appearing tissue masses, the cysts of E. granulosus are surrounded by layers of acellular material (the laminated layer), instead of being separated by cellular sepatae.

Here is a classic example of the laminated layer of E. granulosus:

Here, a small cyst of E. granulosus containing a single protoscolex is surrounded by a laminated layer.

My thanks to everyone who wrote in on this challenging case!