Monday, December 29, 2008

Case of the Week 51

The following is a "squash prep" of muscle tissue submitted from a Peruvian man with muscle aches and diffuse swelling. The coiled objects measure approximately 18 microns across. Identification? (CLICK ON IMAGES TO ENLARGE)

Sunday, December 28, 2008

Answer to Case 51

Answer: Trichinella spp. larvae
Congratulations to Chris, Sue, Anonymous, and the UVM resident who wrote in with the correct answer. This is a beautiful example of Trichinella larvae in skeletal muscle. Unlike the 2-dimensional histologic section, the squash preparation allows you to visualize the 3-dimensional nature of the larva in the muscle nurse cell. To faciliate this type of preparation, you can either press the muscle between 2 glass slides, or use a specially designed instrument - the Trichinelloscope. There is also artifical enzymatic digestion and PCR, both which can be used to identify Trichinella sp. from muscle biopsies.

Monday, December 22, 2008

Case of the Week 50

Happy Holidays!
Can you guess who's in the hat?

Sunday, December 21, 2008

Answer to Case 50

Thank you all for entertaining answers! The top 2 are:
Ancylosantus nicholas
Ancylostoma duodenale, going to a Christmas party

Happy Holidays!
And Happy 50th Case of the Week Anniversary!

Monday, December 15, 2008

Case of the Week 49

The following object was identified in the feces of a 30 year old immigrant from Mexico.
Upon manipulation, the following was extracted. Identification?

Answer to Case 49

Answer: Taenia proglottid (fragment) and egg.

This case demonstrates that not all specimens are picture-perfect. Only a portion of a proglottid is present and the egg obtained is partly obscured. However, the outer radial striations and inner hooklets are visible, allowing definitive diagnosis.

Monday, December 8, 2008

Case of the Week 48

A patient has recurrent fevers after returning from 'Adventure travel' in Africa. He claims to have received all of his pre-travel vaccinations and took his malaria prophylaxis regularly while there. A peripheral blood smear shows the following. Identification? Be as specific as possible.

Sunday, December 7, 2008

Answer to Case 48

Congratulations to Heather! She accurately identified this organism as Plasmodium vivax, based on the following features:

"amoeboid organisms; Schuffner's dots; 1 1/2-2X enlarged RBCs; light, "lacy" lavendar-colored organisms".

Great description. Based on the enlarged red blood cell and the stippling, your differential diagnosis would be P. ovale. However, this species produces trophozoites that are not amoeboid and much more compact. If you're 'lucky', RBCs infected with P. ovale are also ovoid with fimbriated edges, although this is only seen in a minority of infected cells.

Monday, December 1, 2008

Case of the Week 47

The following worm was unexpectedly identified in a duodenal washing. It is approximately 14 microns in length. From this video, what organism would you suspect?


Answer to Case 47

Answer: Strongyloides stercoralis
This was a challenging case. The way I would approach identification is as follows. First, you want to know what general category you would place this worm; for example, is it a cestode, nematode, or trematode. You can tell from the video that it's a nematode (round worm). Next, I would formulate a differential diagnosis based on it's size and location (small bowel). This would place Strongyloides at the top of your list, although you would want to do a permanent mount of the worm to confirm it's identity.

Tuesday, November 25, 2008

Case of the Week 46

The following was submitted for identification to the parasitology laboratory. It was found on a patient's leg and the clinician queried myiasis, although there was no apparent wound in the patient's skin. What should you tell the concerned physician?

Monday, November 24, 2008

Answer to Case 46

Answer: You should tell the clinician that this is likely a free living insect larvae and that there is no need for further concern. In this instance, the clinical presentation does not suggest myiasis since the larvae was not found within human tissues. Furthermore, this larva clearly has legs, which is NOT a feature of myiasis-causing fly larvae.

Upon further questioning, the patient reported what appeared to be a moth's nest in the box springs of his bed. The nest contained larvae that were identical to what is shown.

Monday, November 10, 2008

Case of the Week 45

The following worms were removed from the small bowel during colonoscopy. At the time of the procedure, the endoscopist noted several punctate hemorrhages in the surrounding mucosa and rightly concluded that these represented previous attachment sites for the worms.

Light microscopy of the mouthparts revealed the following.


Sunday, November 9, 2008

Answer to Case 45

Answer: Hookworm. Necator americanus. You can distinguish N. americanus from the other hookworm Ancylostoma duodenale but the presence of cutting plates instead of teeth. See Case of the week 3 for an example of Ancylostoma mouth parts.

Monday, November 3, 2008

Case of the Week 44

The following is a routine hematoxylin and eosin stained histologic section of small bowel. The patient presented with watery diarrhea. Identification? What would a likely clinical scenario be for this infection. CLICK ON IMAGES TO ENLARGE.

Answer to Case 44

Answer: Giardiasis
Note that the organisms are cut in various planes so that you only rarely see a perfect pear shaped organism with 2 nuclei.

As part of this case, I asked the readers to propose a hypothetical scenario on how this infection was acquired. These are some of the answers I received:

1. Young, idealistic univerisity graduate takes the year before medical school to hike from Katahdin to Springer on the Appalachian Trial. Along about early October, somewhere in Blue Ridge of North Carlolina/Tennessee, after testing the limits of "minimalism" and ceasing to filter-sterilize his drinking water, he develops diarrhea so profuse that he's forced to hole up in a remote shelter for several days to regain strength. It is there that he first entertains a notion that the seemingly pristine "mountain streams" probably do serve as primary watershed for the many high-elevation pastures of nearby dairy and beef herds.

2. "Parasite Gal" and husband go hiking in the woods, get thirsty, and drink unfiltered water from a stream. Then, 24 hours later, they wish they were back in London.

I must admit that I am less fond of the second scenario, since it involves me personally!

Thank you for the creative responses.

Monday, October 27, 2008

Case of the Week 43

This weeks case may look familiar (hint: we've seen a similar case on Creepy Dreadful Wonderful Parasites before) but I thought that these pictures were so striking that I wanted to share them with you.

The following were submitted to the laboratory on a glass microscope slide. No history. Identification? (CLICK ON IMAGES TO ENLARGE)

Answer to Case 43

Answer: Pthirus pubis, the crab louse.

Little known facts about the crab louse:
1. It's an obligate parasite, living and feeding only on humans.
2. It takes 4 to 5 blood meals a day.
3. The closely related body louse feeds even more frequently and can cause anemia in heavily infected individuals. Historically, children with louse-induced anemia looked pale and unwell - this is where the term "lousy" came from.
4. The crab louse most commonly inhabits the genital area but can also inhabit the hair under the arm pits, eye brows, and eye lashes. The latter may be seen in children and does not necessarily indicate sexual abuse; infection can be passed from one child to another through casual contact.

Monday, October 20, 2008

Case of the Week 42

Cross-sections through an appendix removed for acute appendicitis revealed the following:
(H&E stained histologic images, Click to enlarge)

Answer to Case 42

Answer: Enterobius vermicularis (pinworm)
Shown are cross-sections of the adult worms within the lumen of the appendix. In some cross-sections you can see the characteristic eggs within the females (below is the egg in a stool iodine prep from a different patient).

What is also classic about this case is the location (appendix and cecum are traditional locations for the adult female pinworm) and the lateral alae on the worms. Alae, (plural of ala, Latin for 'wing') are longitudinal ridges seen in the larval forms of nematodes, (e.g. Ascaris lumbricoides), and the adult worm Enterobius vermicularis. In fact, Enterobius is the only ADULT worm with these ridges that parasitizes humans. Below is the cross-section from this case showing the lateral alae (arrows) as well as a longitudinal view of the adult worm in an iodine stool prep (arrow marks the ridge on one side of the worm). The ridges extend the length of the worm.

Tom was correct in mentioning Toxocara spp. since the larval form causes visceral larva migrans in humans. However, the larva are much smaller than the adult E. vermicularis and would be seen within the parenchyma of tissues (e.g. liver) in association with a marked inflammatory response.

Monday, October 13, 2008

Case of the Week 41

The following were seen in a papanicolaou-stained urine preparation. These objects range in size from 20 to 50 microns.

Answer to Case 41

Answer: crystals (urate)
Great job to everyone who got this one. Crystals in urine are a common mimic of parasite eggs. The ways to distinguish them from the real thing are as follows:
1. Parasite eggs will have internal staining structures on Pap, Giemsa, and H&E stains, whereas crystals will be colorless or only slightly pigmented.
2. Parasite eggs are uniform in size, whereas crystals will show greater size variation. In this case, the crystals were also much smaller than the Schistosoma eggs that they mimicked.
3. Crystals will often show cracking artifacts and appear refractile.
4. Crystals will not reliably show the defining features of parasite eggs. In this case, they mimicked both Schistosoma mansoni and S. hematobium eggs. However, the spines were never completely characteristic. For example, S. hematobium eggs have a spine at only 1 terminus (instead of both ends like the urate crystals shown).

Below is a true S. hematobium egg (left) to compare to the urate crystal (right). They are shown at approximately the same magnification to highlight the difference in sizes.

Monday, October 6, 2008

Case of the Week 40

Skin scrapings from a pruritic rash. Identification?

Sunday, October 5, 2008

Answer to Case 40

Answer: Scabies eggs and fecal pellets.

Monday, September 29, 2008

Case of the Week 39

Autopsy of an eldery immunocompromised woman with no travel history outside of the U.S. Shown are sections of necrotic large bowel and necrotic luminal material.

Answer to Case 39

Answer: Strongyloidiasis, showing mucosal invasion by Strongyloides stercoralis larvae. Note the marked intestinal mucosal necrosis and high larval load. Great job Tom and Heather!

Monday, September 22, 2008

Case of the Week 38

No tricks here - just a simple identification.

Bonus question - what is the infective form of this organism?

Answer to Case 38

No responses to this one - I guess I made it too easy? This is a beautiful example of a Trichuris trichiura or whipworm egg. Note that it is a mature specimen; the egg has embryonated and there is now an easily visible larva inside. It is unusual to see eggs in this advanced state of development since maturation usually occurs in the soli.

To answer the second question: the infective form is the embryonated egg shown here. It is ingested in fecally contaminated food or water, and the larvae hatch in the small intestine. The adults then take up residence in the cecum and large intestine.

Monday, September 8, 2008

Case of the Week 37

The following was seen in a peripheral blood smear in a traveler from Africa. I don't have a low power view, but these high power images should give you enough to make the diagnosis. (CLICK ON IMAGES TO ENLARGE)

Answer to Case 37

Answer: Wucheria bancrofti

Ok, I admit this was a hard case. There are several morphologic features present in these images to point you to an identification; unfortunately, some are conflicting. However, this is a real case and one that initially stumped us in the laboratory as well. Below are the steps I use for speciating microfilariae based on morphologic features:

First, I look for is the presence or absence of a sheath. Only 3 microfilariae have a sheath, so this immediately helps to focus your answer. For those of you that like memory aids, you can remember the 3 sheathed microfilariae by the following phrase: Wears Long Britches. The first letter of each word (W.L.B.) is the first letter of each organism: Wucheria bancrofti, Loa loa, and Brugia spp. Think of the "long britches" as the sheath over the worm's "leg".

If you identify the sheath, then look to see if the sheath stains with giemsa. The sheath of W. bancrofti and L. loa doesn't usually stain, and thus appears as a negative image, while the sheath of Brugia is usually bright pink. The sheaths of the first 2 organisms do stain pink with hematoxylin and eosin, so it's important to know what stain you're looking at (shame on me for neglecting to include this information).

This is where most will get out their atlases and look up the other specifics such as length of the worm, position of nuclei relative to the tail, characteristic of the nuclei and the tail, and the size of the cephalic space. Finally, travel history is essential, since the filarial worms have different geographic distributions.

So for this case, the overall length (approx. 300 microns), presence of a sheath, short cephalic space, and lack of nuclei in the narrow pointed tail indicated that this was W. bancrofti. Furthermore, the patient was from Africa, and had no history of travel to Asia, which would be expected to make a diagnosis of Brugia spp. The only feature that didn't quite fit was the fact that the sheath was stained pink with giemsa. Well, I guess you can't have it all....

Thank you to everyone who wrote in on this case. It just goes to show that real-life is rarely as easy as the textbooks.

Monday, September 1, 2008

Case of the Week 36

The following are touch-preps from a brain biopsy. Identification? (CLICK ON IMAGES TO ENLARGE)

Answer to Case 36

Answer: Toxoplasmosis; tachyzoites of Toxoplasma gondii seen.

This was a very challenging case since the multiple small objects (the tachyzoites) blended in with the surrounding tissue. However, if you click on the second image (also shown below), you get a larger view where it is easier to make out the organisms. I've added some arrows to highlight 2 of the tachyzoites that have a particularly nice arc shape. (CLICK ON THE IMAGE TO ENLARGE)

I posted this case because it is what you may expect to see in real life. When available, the clinical history, serology and radiology can help support the diagnosis. Thanks to everyone who was brave enough to write in on this case!

Sunday, August 24, 2008

Case of the Week 35

Name 2 important histologic findings in the following bladder biopsies. (CLICK ON IMAGES TO ENLARGE)

Saturday, August 23, 2008

Answer to Case 35

Answer: Urinary schistosomiasis with Schistosoma haematobium and adenocarcinoma of the bladder.

I admit that it wasn't quite fair to expect a diagnosis of cancer on just a few fields, but having seen this whole case, I can confirm that this is indeed adenocarcinoma. This is an unusual case, since schistosomiasis is usually associated with squamous cell carcinoma and not adenocarcinoma. However, it could be that the two findings are completely unrelated.

Of interest, you can see the terminal spine on one of the partially calcified eggs in the middle image, confirming that this is S. haematobium.

Monday, August 18, 2008

Case of the Week 34

Here is a simple identification. Feel free to be as general or as specific as you like, based on your expertise (and interest!).

Answer to Case 34

Wow, what a great response I had to this case! It is a beautifully ornamented tick, so I guess I'm not too surprised that it caught people's interest.

This is a male Amblyomma variegatum, also known as the Tropical African Bont Tick. It is found in the tropics and subtropics, including some islands of the Caribbean. You might notice from the photo that it has long mouth parts. Because of this, it tends to leave large (and painful) bite wounds.

It is a vector of several organisms causing veterinary disease (such as Heartwater fever), as well as Rickettsia africae, the agent of African tick-bite fever, and Crimean-Congo hemorrhagic fever virus. It may also carry a number of other viruses such as Dugbe, Thogoto, Bhanja , and Jos.

Congratulations to Karma453 for the correct answer, and to Anonymous for the follow-up answer. Also, special bonus points to F. and W. for their creative guesses that made me smile.

Saturday, August 9, 2008

Case of the Week 33

The following lymph node biopsy was taken from a boy with no travel history outside of the U.S. He had presented with acute onset of fever and lymphadenitis.
Diagnosis? What is your differential diagnosis? (CLICK ON IMAGES TO ENLARGE)
Images courtesy of Dr. Thomas Trainer

Answer to Case 33

Answer: Toxoplasma gondii lymphadenitis. This is a rare case in that cysts are not typically seen in the affected lymph nodes. Instead, pathologists rely on the classic pathologic features (e.g. lymph node architecture and pattern of inflammatory cells) to suggest the diagnosis, which should then be correlated with clinical features and serologic tests.

Findings that may mimic the cysts of T. gondii include T. cruzi pseudocysts and macrophages with Leishmania spp. amastigotes or Histoplasma capsulatum yeasts.

Monday, August 4, 2008

Case of the Week 32

The following was extracted from the arm of a traveler to South America. Identification?