Dirofilariasis, a rare subcutaneous infestation

This is a pretty rare infestation. It's called dirofilariasis. Filarial roundworms migrate to the subcutaneous plane in this patient with formation of a cystic complex lesion in the thigh. 

Sometimes, live dirofilarial worms may be seen, forming the dirofilariasis worm dance. 

What is the differential diagnosis:

It may be difficult to differentiate such a lesion from cysticercosis.

The dirofilarial dance sign if present is diagnostic. 

Images courtesy of Dr Golam. 

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Musculoskeletal ultrasound