Subcutaneous dirofilariasis: a masquerade of a palisaded granulomatous dermatitis

Dirofilaria species are roundworms responsible for "heartworm" in canines. On occasion, humans are an accidental host, resulting in pulmonary (Dirofilaria immitis) or extrapulmonary (Dirofilaria repens) manifestations. Of the extrapulmonary sites of involvement, subcutaneous involvement is particularly common. We report a case of a 49-year-old female who presented with an erythematous nodule on her shin, which closely resembled necrobiosis lipoidica on histopathologic examination. On closer examination, there were foci of necrosis that harbored segments of the nematode, diagnostic of dirofiliarisis. We present this case to highlight the histopathologic similarities and differences between palisaded necrobiotic conditions and this potentially underrecognized entity.