Monday, December 28, 2009

Case of the Week 99

Welcome back Readers to the last case in 2009! I think it is very fitting that this is Case 99, and that Case 100 will be the first case of 2010.

This case is a colon biopsy that contained an unexpected object:
For the non-pathologists, note that what we're seeing is a worm cut in cross-section. Use the internal structures to help you identify it. Another hint: notice that the worm portion shown is external to the intestinal mucosa.


Sunday, December 27, 2009

Answer to Case 99

Congratulations to everyone who recognized the bipolar plugs of the eggs inside this cross section of Trichuris trichiura. This was a tricky case, but the location of the worm helps (colon lumen), and the eggs are diagnostic. Although the eggs are reminiscent of hookworm (as suggested by one viewer), that is largely due to the fact that the cytoplasmic contents of the eggs have retracted from the wall (probably as an artifact of fixation). The thick wall and bipolar plugs are the most useful features.

Happy New Year to all of my parasitology friends!

Monday, December 21, 2009

Case of the Week 98

Here's a challenging case for you to start off the holiday week:
The following eggs were seen in a stool preparation from a 2 year old boy with vague abdominal pain. They measure approximately 50 microns in greatest dimension. Identification?

Sunday, December 20, 2009

Answer to Case 98

Answer: Hymenolepis nana eggs
Most people who wrote in with the answer to this were correct - these are good examples of the thin-walled H. nana eggs, with a central 6-hooked embryo, and 4 to 8 polar filaments radiating from thickenings of the envelope surrounding the embyro (onchosphere). The eggs measure between 30 to 50 microns in diameter.

H. nana, also known as the dwarf tapeworm, most commonly infects children, and is acquired through ingestion of eggs, or infected beetles (the intermediate host). The usual definitive host is a rodent.

Monday, December 14, 2009

Case of the Week 97

Blood smear from a febrile missionary who just returned from Nigeria. Diagnosis?

Sunday, December 13, 2009

Answer to Case 97

Answer: Plasmodium ovale (trophozoites)
Congratulations to everyone who wrote in with the answer - you all recognized the classic appearance of P. ovale in a thin smear of peripheral blood. Like P. vivax, P. ovale has prominent stippling (a.k.a. Schuffner's dots) and enlargement of the infected red blood cells, but the trophozoite forms are more compact than P. vivax, and many of the infected red blood cells (approximately 1/3) are elongated or oval in shape (hence the name ovale). In addition, one edge of the infected cells is often ragged or fimbriated. The characteristic features are outlined below:

Wednesday, December 9, 2009

Interesting PodCast

Here's an interesting podcast on how a lack of biodiversity might increase the rates of human disease, including malaria.

To hear the part of interest, fast forward to the 2 min, 22 second mark.

Monday, December 7, 2009

Case of the Week 96

The following was found on the scalp of a 60 year old woman. Identification?

Sunday, December 6, 2009

Answer to Case 96

Answer: Pediculus humanus, Human head or body louse.

Many of you were very observant and noticed that there was a similar image on my front page:

Thanks for writing in!

Sunday, November 29, 2009

Case of the Week 95

The following objects were aspirated through a fine-gauge needle along with fluid from a slowly growing cystic mass. Papanicolaou stain. No further information is available. (CLICK ON IMAGES TO ENLARGE)

(600 times original magnification)

Saturday, November 28, 2009

Answer to Case 95

Answer: Protoscoleces and hooklets of Echinococcus spp.

The fact that this is a single cystic mass, and that protoscoleces are present suggests that this is E. granulosus instead of E. multilocularis, but clinical and radiographic correlation is necessary for definitive speciation. E. granulosus typically produces a single, slowly growing cyst, that may eventually contain one or more daughter cysts - each containing protoscoleces (the so called 'cysts within a cyst' appearance) - while E. multilocularis typically produces multiple, rapidly growing cysts that expand in a invasive fashion, and are not constrained by an outer cyst wall. E. multilocularis cysts rarely contain protoscoleces in humans, but are often 'sterile'. These 2 species are the most common to infect humans, but other species rarely infect humans as well.

Thank you all for the great comments on this case! I especially enjoyed "I am hooked on Echinococcus" by Scott and Anonymous.

Monday, November 23, 2009

Case of the Week 94

The following objects were found in a Papanicolaou-stained urine specimen. The intact object measures approximately 170 µm long by 50 µm wide. Identification?

(I'd like to thank Drs. Gladwyn Leiman and Ann Berry for these beautiful images!)

Sunday, November 22, 2009

Answer to Case 94

Schistosoma hematobium egg.
The distinguishing features of this eggs are its large size (>100 microns in length), and characteristic terminal spine. The fact that they are found in urine is another important feature, since these eggs are usually laid around the venus plexus of the bladder, and some eventually make their way through the bladder wall into the urine.

What is striking about this case is the associated inflammatory response. Note here how the egg has been badly damaged by the adherent collection of inflammatory cells.

Even more striking is this image of a multinucleated giant cell that is trying to engulf an egg intact!

One writer asked why the eggs were stained. This is a good point, since we don't typically stain urine specimens in the microbiology lab. However, this was a specimen that was submitted to cytology and was subjected to Papanicolaou (pap) staining. The eggs are easily identified both with and without staining, but the pap stain nicely highlights the inflammatory response, and makes for some striking images!

Monday, November 16, 2009

Case of the Week 93

The following objects were identified from a concentrated wet mount preparation of stool. The patient was originally from China, and has a history of cirrhosis. Identification?

Sunday, November 15, 2009

Answer to Case 93

Answer: Fasciola hepatica
Congratulations to everyone who wrote in on this case! You all recognized that this egg falls into the category of thin-walled oval operculated eggs, which includes (in increasing size) Clonorchis sinensis, Diphyllobothrium latum, Paragonimus westermani, and Fasciola hepatica/Fasciolopsis buski. I put the last 2 eggs together since they are morphologically indistinguishable - although they are from 2 distinct flukes that inhabit different regions of the body.

There are subtle differences between these 5 eggs, but they can be easily confused for one another. That is why it is essential to MEASURE your eggs using an ocular micrometer so that an accurate identification can be made. Of interest, these 5 eggs are from 4 flukes and 1 cestode. This just shows that there is morphologic overlap between very different phyla of parasitic worms.

Monday, November 9, 2009

Case of the Week 92

The following insect was found in a patient's home in the Northeast U.S. The patient wanted to know if he should be concerned about potential disease transmission.
What is the identify of this insect? What would you tell the patient's physician?

(Note - this is a good example of how insects are submitted to the laboratory for diagnosis. They are rarely in perfect condition!)

Sunday, November 8, 2009

Answer to Case 92

Well, it turns out that this case is much more complicated than I originally thought. I was going to call this a Reduvid bug, from the Reduviidae family, which includes "Assassin" or "kissing" bugs. Assassin bugs are the vectors of Chagas disease (Trypanosoma cruzi). There are over 135 species in North America, but fortunately, Chagas disease is limited to the southern most portion of the U.S., and is primarily in Central and South America.

However, in showing these photographs to my entomology friends, they comment that this bug may be either a Reduvid bug or one of the leaf-footed bugs (family Coreidae), that has approximately 80 species in N. America. Damsel bugs (Family Nabidae) can look similar too, but are usually small (3mm to 1 cm). Since the insect is no longer available for further examination, I'm afraid that the final identification will remain a mystery.

Fortunately, the 2nd part of my question is easier to answer - how you should advise the patient's physician. Regardless of this bug's identification, it is not likely a vector of human disease, unless it had gotten to New York state by stowing away in someone's luggage from a region that is endemic for Chagas disease. Therefore, you can reassure the physician that this bug does not pose a risk to his or her patient.

Monday, November 2, 2009

Case of the Week 91

The following object was seen in the stool of a Mexican immigrant and brought to the lab for identification. (CLICK ON IMAGES TO ENLARGE)

The fluid expressed from the object contained the following:


Sunday, November 1, 2009

Answer to Case of the Week 91

Answer: Taenia spp. adult tapeworm
Shown here is a long segment of proglottids which had been shed intact in the patient's feces. To confirm the diagnosis, fluid was expressed from the proglottids, and provided the following eggs. Note the thick striated outer wall and inner hooklets, with is classic for Taenia eggs. As a note - If you see hooklets inside a helminth egg, then you know you are dealing with a cestode.

The presence of diagnostic eggs allows for identification to the genus level. However, speciation requires examination of the uterine branches within a mature gravid proglottid (e.g. through india ink injection), or examination of the scolex (if found). In this case, the specimen was submitted in formalin which interfered with our ability to inject india ink into the uterine branches. Since no scolex was found, we were not able to provide definitive speciation in this case.

Salbrent mentions the following important point: "all Taenia eggs and proglottids must be handled with extreme care b/c T solium eggs are infective to humans." This is essential to remember when handling proglottids! Accidental ingestion of T. solium eggs can lead to cysticercosis, where humans serve as the intermediate host of the tapeworm - a much more deadly disease than intestinal infection with the adult tapeworm. Eggs can remain infectious for months, even in fixatives such as ethanol or formalin. So wear gloves whenever handling tapeworm proglottids, and wash hands well afterward.

Monday, October 26, 2009

Case of the Week 90

The following photos are from a Giemsa-stained slide of corneal scrapings from a patient with a painful red eye.

Sunday, October 25, 2009

Answer to Case 90

Answer: Acanthamoebic keratitis

This is a case of keratitis caused by Acanthamoeba species. These protozoan parasites are free-living amoebae found widely in the environment, such as in fresh water pools, soil, dust, and even chlorinated tap water. Keratitis usually occurs in patients that wear contact lenses, since the lens provides a nidus for irritation and infection. The classical history is that of a patient who wears contact lenses and rinses them in tap water or home-made saline solution.

The diagnosis is made by identifying classic cysts and/or trophozoites in corneal scrapings or biopsies, (histopathology, cytopathology, or microbiology preparations). Acanthamoeba spp. can also be grown in culture or detected using fluorescent and molecular methods. Trophozoites measure approximately 15-45 µm, and produce many spine-like processes (acanthapodia) in culture. They differ from Entamoeba histolytica trophozoites by having a large nucleus, large, centrally-located karyosome, and no peripheral chromatin. The cysts are typically 10-25 µm in diameter, and have a classic morphology, with a double-walled cysts. The outer wall (exocyst) is typically wrinkled, while the inner wall (endocyst) is hexagonal, spherical, or star-shaped. Like the trophozoites, the cysts contain one nucleus. CLICK ON IMAGES TO ENLARGE

Culture on tap water agar - See Previous Case of the Week.

Another important differential diagnosis in this scenario is herpes keratitis caused by herpes simplex virus. One viewer commented that the organisms appeared to have the classic "marginated chromatin, glassy/cleared-out nuclei" of HSV-infected cells. This is particularly relevant in this case, since the cysts do not have visible nuclei. However, they can still be differentiated from herpes-infected cells by the presence of the wrinkled double walls. Also, the classic features (the 3 "M's") of herpes are not present - Multinucleation, nuclear Molding, and Margination of nuclear chromatin. Below is a classic case of a multinucleated herpes simplex virus-infected cell.

This patient with acanthamoebic keratitis did well after treatment, with little residual scarring. However, this is not always the case, and many cases of keratitis are very refractory to treatment.

A more deadly presentation of Acanthamoeba spp. is chronic granulomatous encephalitis, a slowly progressive, often fatal infection of immunocompromised patients. Disease usually disseminates from a primary dermal or pulmonary source, cysts may be found in the skin, lungs and other organs.

Thanks to all who wrote in with comments!

Monday, October 19, 2009

Case of the Week 89

A farmer presented with bloody diarrhea and abdominal cramps. Endoscopy revealed multiple ulcers, and the following biopsies were obtained:


Answer to Case 89

Answer: Balantidium coli
This parasite is unique in 2 aspects: it is the largest protozoan parasite and the only ciliated parasite to infect humans. Like amebiasis, the site of infection is typically the large intestine, where it can cause invasive disease, bloody diarrhea, fever, and abdominal pain. This case is a good example of invasive disease with mucosal ulceration (below).

Within the ulcer and intestinal mucosa, the large ciliated trophozoites can be seen.

The trophozoites are large (typically > 50 microns) and have a vacuolated cytoplasm and a classic dark "kidney-bean" shaped macro-nucleus. These features allow these trophozoites to be distinguished from those of Entamoeba histolytica, which are smaller (20 microns) and have a smaller, less distinctive nucleus. In the image below, only a partial cross-section of a trophozoite is seen, and so the full diameter is not appreciated.

A second trophozoite shown below is clearly larger and is surrounded by a "fuzzy" layer, which represents the cilia.

Here is an image from a trichrome-stained fecal smear that more clearly shows the "kidney-bean" shaped macronucleus and surrounding cilia.

Finally, Dr. W. reminds us that Balantidium coli trophozoites have a particular type of motility. She states "When I first encountered this parasite as a path resident and learned that its motility was "boring", I thought that meant that the motility was uninteresting". Indeed, the motility is "rotary" or "boring". Great story!

Thanks to everyone who wrote in with comments.

Monday, October 12, 2009

Case of the Week 88

Here is an unusual case for you.
The following objects were seen in a bowel resection:

I'll give you a hint - the organisms look the same as they normally would, but they are not where you would expect them to be.