Sunday, May 20, 2012

Case of the Week 209

The following liver biopsy is from 6 year old girl. 

Hematoxylin and eosin (H&E), 200 times original magnification

 H&E, 400 times original magnification 

H&E, 1000 times original magnification
Based on these findings alone, what is your differential diagnosis?

The following object was found in the soil from the backyard where she frequently played.

 Unstained, object measures approximately 60 microns in diameter


Saturday, May 19, 2012

Answer to Case 209

Answer:  Visceral larva migrans caused by Toxocara spp.

The images of the liver show a single section of a larval nematode within a granuloma.  The larva is surrounded by multinucleated giant cells and an outer rim of lymphocytes.  Based on this image, the main differential diagnosis is toxocariasis and balisascariasis.  Other nematode infections that should be considered also inlude gnathostomiasis, ascariasis due to Ascaris suum, and capillariasis due to C. hepatica. 

The morphologic features that allow the diagnosis of Toxocara spp. from these other nematodes are:
1.  Only a small larval form is seen.  The diameter of Toxocara canis is 18-21 microns, while the diameter is T. cati is 15-17 microns.  In comparison, the diameter of Gnathostoma and Ascaris larvae (especially third stage larvae) is usually much larger, and larvae are not seen in Capillaria hepatica infections.
2.  Lack of a patent intestine in Toxocara.  The other organisms mentioned have a patent intestine, even when only present as larvae.
3.   Adult forms are not present.  In capillariasis, adults, and often characteristic eggs, are seen.
4.  The presence or absence of lateral alae may be helpful in the differential.  In this case, no cross-sections were identified and so it is not possible to determine if alae are present.  However, here is the break-down of relevant larval worms and whether or not they have alae:

Toxocara spp. - lateral alae present, single ala on each side
Baylisascaris spp. - lateral alae present, single ala on each side
Ascaris spp. - lateral alae present, single ala on each side
Gnathostoma spp. - no lateral alae
Capillaria hepatica - larvae not seen in human liver; no alae in adult worms

Finally, the presence of this larva in the liver and the young age of the host is classic for toxocariasis.

The image below the histopathology photos shows the characteristic egg of Toxocara spp.  Note the classic thick pitted shell. Inside is a coiled larva, indicating that it is infectious. These eggs are never seen in human feces but are commonly seen in the feces of un-wormed dogs and cats.  The eggs of T. canis are slightly larger (75-85 microns in diameter) than those of T. cati (65-75 microns in diameter) and the shell is more finely pitted in the latter. 

Monday, May 14, 2012

Case of the Week 208

The following case was generously donated by MicrobeMan:

The patient is a 70-year-old woman who presented with 2 weeks of fever, chills, and progressive jaundice.  She had received an orthotopic liver transplant 3 years prior.  On admission, she was noted to have acute renal failure and she was started on antibiotics for a presumed urinary tract infection.  However, peripheral blood films showed the following:


Sunday, May 13, 2012

Answer to Case 208

Answer:  babesiosis

Great discussion on this case!  Based on morphology (since I didn't provide an exposure history), most readers thought this was infection with either Plasmodium falciparum or Babesia spp.  Indeed, these are the top 2 parasites in the differential since both share the following features:
1.  The size of the infected RBC is not enlarged
2.  Parasite forms are limited to ring-shapes
3.  Ring forms are relatively small and delicate
4.  Multiply infected RBCs are present

What allows Babesia spp. to be differentiated from P. falciparum in this case, however, are the following features:
1. There is marked parasite pleomorphism, with spindled, oval, and round forms
2. There are more than 2 rings per RBC, which would be unusual for P. falciparum

Other features that are helful for differentiating P. falciparum from Babesia (although not seen in this case) are tetrad forms (so-called "maltese crosses") and extracellular rings.  The former are diagnostic of babesiosis, but are rarely seen in clinical cases.

In this case, the patient unfortunately died of her disease.  Sequencing at the CDC later showed the species to be the MO-1 strain described recently in Missouri.

Monday, May 7, 2012

Case of the Week 207

The following were an unexpected finding on anal Papanicolaou-stained pap smear from a male with papular anal lesions.  Identification? (CLICK ON IMAGES TO ENLARGE).


Sunday, May 6, 2012

Answer to Case 207

Answer:  Giardia intestinalis (lamblia, duodenalis) cysts

This was a very fun case because the finding of Giardia cysts was completely unexpected.  As mentioned in the history, this patient was being evaluated by an anal pap smear due to the presence of papular anal lesions which were clinically thought to be condyloma accumulatum (genital warts, caused by human papillomavirus or HPV). 

Patients that have anal-receptive intercourse are at known risk for HPV associated lesions, dysplasia, and malignancy, and therefore screening for HPV-associated cytopathologic changes is commonly performed.  As noted by MicrobeMan and Anonymous, there were some atypical appearing cells (such as the large bi-nucleated pink structure in the center of the slide) indicating that there were some HPV changes present in this case. 

This case was signed out as "Squamous Epithelial Cell Abnormality.  Atypical squamous cells of undetermined significance. Organisms consistent with Giardia intestinalis."

Of note, the patient denied any gastrointestinal symptoms including diarrhea.  So the giardiasis appears to be an incidental finding!