Saturday, March 26, 2016

Case of the Week 390

The week's case was generously donated by Blaine Mathison. Below are H&E-stained sections of a perineal abscess of a patient diagnosed with Fournier's gangrene with bacterial infection. Identification?

Friday, March 25, 2016

Answer to Case 390

Answer: Blastocystis hominis

This was a very unusual and interesting case which generated a lot of great discussion. Thank you for the comments! Blaine (who donated this case) and I both believe that this case represents contamination/colonization of pre-existing fasciitis with B. hominis in a patient with Fournier's gangrene, rather than primary infection with this parasite. Fournier's gangrene is an extensive and rapidly-progressive polymicrobial fasciitis often seen in the setting of impaired host response (e.g. diabetes) and is usually precipitated by local trauma. The necrotizing process commonly originates from the anorectal tract, which might explain how B. hominis came to be involved.

This case gives us a rare opportunity to see the classic vacuolar forms of B. hominis in H&E-stained tissue sections. They have a very similar appearance to what we see in stool exams, with a large central vacuole and peripheral nuclei.

Monday, March 14, 2016

Case of the Week 389

This week's case was generously donated by Dr. Eric Rosenbaum who received the following in his laboratory. Identification?

Sunday, March 13, 2016

Answer to Case 389

Answer: Human Bed bug (Cimex sp.)

This case shows the characteristic features of a bed bug, including the flattened body, brown-red color, segmented abdomen, vestigial wings (wing pads), and setae (hair-like structures covering the body).

The 2 species of bed bugs that are most commonly implicated in human infestations are Cimex lectularis, the common bed bug, and C. hemipterus, the tropical bed bug. Rarely, humans can also be incidental hosts of Cimex species of bats and birds, especially when the natural hosts are in or living near human dwellings. It is important to differentiate human and zoonotic bed bugs, since the management is usually different. The best way to do this is by examining the length of the setae. Human bed bugs have setae that are shorter than the width of the eye, while bat and bird bed bugs have setae that are longer than the width of the eye. You can appreciate this somewhat in this case:

Sunday, March 6, 2016

Case of the Week 388

This week's case is from Emily F. in my lab. No history is available.


Saturday, March 5, 2016

Answer to Case 388

Answer:  Pediculus humanus, not further specified.

As several readers mentioned, knowing the source of the infestation would have been very useful in determining if this is a head or body louse, since these 2 subspecies (P. h. humanus and P. h. capitis) are morphologically indistinguishable, and overlap in size range (although head lice are on the smaller end of the range). Unfortunately, as is often the case, we were not given a source.

Pediculus humanus can be identified by its elongated body and grasping (raptorial) claws as shown below.