Monday, September 28, 2009

Case of the Week 86

The following painless nodule was removed from the subcutaneous skin of the abdomen from an African male. He comments that the skin of his lower extremities is dry, focally depigmented, and extremely itchy.

Sunday, September 27, 2009

Answer to Case 86

Answer: Onchocercoma. Definition: a subcutanteous tumor-like mass caused by the presence of adult filarial worms Onchocerca volvulus. Note the fibrous tissue surrounding the coils of the adult worms, and the microfilariae within the classic 'double uterus' and in the surrounding tissue. All adult female filarial worms that infect humans have a classic double uterus, seen best in cross-section.

The disease caused by Onchocerca volvulus is called onchocerciasis. The symptoms are caused almost entirely by the release of the microfilariae into the surrounding skin where they cause extremely itchy dermatitis. The most severe damage, however, is caused by the migration of the microfilariae through the chambers of the eye, and the retina, resulting in permanent scarring and blindness. Thus, the common name for onchocerciasis is "river blindness". The onchocercoma is typically painless and causes very little symptoms.

In this case, the differential diagnosis includes other adult filarial worms, such as the agents of lymphatic filariasis (i.e. Wuchereria bancrofti and Brugia spp.). These adults are not found in subcutaneous nodules like onchocerciasis, but within lymphatics and lymph nodes. The symptoms of lymphatic filariasis typically include inflammation of the lymphatics (lymphangitis), obstruction of the lymph channels, and eventually scarring, and edema (elephantitis). Unlike onchocerciasis, the disease of lymphatic filariasis is caused primarily by the presence of the adults. The microfilariae are released into the lymphatics, and cause little associated symptoms.

Monday, September 14, 2009

Case of the Week 84

The following images are from a peripheral blood smear from a 93 year old male from Connecticut. No travel history is received.

Answer to Case 84

Answer: Babesia spp.
Congratulations to all of my viewers who got this correct.

Babesiosis is a tick-borne disease, found in North America, Europe, and Asia. It is a mimic of infection with Plasmodium falciparum (which was the 2nd most common answer that viewers gave), since the infected RBCs are not enlarged, the rings are small (1/3 the size of the RBC or smaller), and multiple infections per cell are common. Fortunately, several features allow for differentiation of Babesia spp. from P. falciparum.

First, note that the size of the organisms within RBCs is variable, and that some forms are extremely small (<1/5 the diameter of the RBC). This is typical for babesiosis, and not for P. falciparum.

Second, Babesia spp. tend to produce atypical forms, with multiple chromatin dots, 'double' rings, and chromatin 'tails' such as seen here:

Babesia rings may also be seen outside of the RBC, in the extracellular space.

If you're really lucky, you will see the classic tetrad formation or "Maltese cross" formed when this organism undergoes binary fission. Although this is the image that is commonly shown in textbooks, it is much rarer in real life.

Finally, the travel/exposure history of the patient is very helpful. It wasn't initially available in this case, but we were later told that the patient had no travel history outside of the U.S. He lived in Connecticut which is endemic for Babesia microti.

This was a challenging case, so thanks to all who were brave enough to write in!

Tuesday, September 1, 2009

Case of the Week 83

The following "skin tag" was removed from the groin of a middle-aged male.

Answer to Case 83

Answer: Hard Tick
This was definitely a challenging one - including for me when I first saw this case. I think that most of us are not used to seeing ticks cut in histologic section (usually this isn't necessary for identification!), but there are some characteristic features that allow for easy identification of this case.

First, notice that the organism is mostly external to the skin, and is inserted only at one end. This is the classic presentation for a tick, and would argue against a botfly larva which is mostly inserted into the skin.

In addition, there are useful identifying histologic features as outlined in the image below, including a thick sclerotized cuticle, well-developed skeletal muscle near the mouth parts, and the mouthparts themselves, if present. (CLICK ON IMAGE TO ENLARGE)