Subcutaneous dirofilariasis caused by Dirofilaria repens diagnosed by histopathologic and polymerase chain reaction analysis.

A 31-year-old man with a history of intravenous drug abuse presented with an inflamed subcutaneous nodule in his left thigh. The nodule measured up to 1.2 cm in largest diameter. Under the clinical impression of an inflamed epidermal cyst or a subcutaneous abscess, surgical excision was performed. Histopathologic examination of the nodule and subsequent polymerase chain reaction (PCR) analysis revealed the presence of the helminth Dirofilaria (D.) repens, a member of the family Filarioidea. Dirofilariasis is a parasitosis caused by D. repens and D. immitis that most frequently affects canines. It can rarely be found in humans, usually in the form of a subcutaneous nodule. In Europe, most cases of human dirofilariasis have been detected in the Mediterranean countries, Ukraine and Russia, but sporadic cases have also been reported in central and north European countries. Dirofilariasis must be distinguished from other forms of filarial disease such as onchocercosis and Wuchereria bancrofti filariasis. Diagnosing dirofilariasis purely by histopathology has its pitfalls, especially when the morphology of the nematode is altered due to inflammatory response or surgical artifacts. PCR analysis offers an opportunity to confirm dirofilariasis and identify the dirofilarial species as well. Briefly, we conclude that a diagnosis of subcutaneous dirofilariasis should be considered in cases of subcutaneous mass in an endemic area of animal dirofilariasis.