Sunday, September 13, 2015

Answer to Case 364

Answer:  Dirofilaria species

As several readers pointed out, the characteristic features in this case are the multi-layered cuticle with external ridges (arrow heads), polymyarian musculature, and well-defined internal cuticular ridges near the base of the lateral chords (arrows).

It's difficult to tell from the images if the central tube is part of the GI tract or male reproductive tract, given the degenerated nature of the nematode and neutrophilic infiltrate. As is common with dirofilariasis, worms are often in an advanced state of degeneration by the time they are removed and observed in tissue sections. Fortunately, some of the characteristic features of the cuticle are nearly always present and allow a diagnosis to be made based on morphology.

Dirofilaria repens and D. tenuis are the most common cause of subcutaneous and ocular dirofilariasis in humans. Given that the patient has not traveled outside of the United States, D. tenuis would be the most likely of the two.

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