Dirofilariasis: a parasitic cause of subcutaneous nodule

Abstract

An 87-year-old French woman presented with a 2-cm diameter nodule of the infra-orbital edge. The nodule (see Supplementary material, Fig. S1) was subcutaneous, mobile with respect to the underlying structures, and had never been either inflammatory or painful. The patient had no particular past medical history or habitus except that she spent 3 months each year in Italy with her dog. Due to recent discomfort, surgical excision was performed. Anatomical pathology showed a fibro-inflammatory reaction containing some eosinophils surrounding sections of a worm with a diameter of c.500 μm and ornamented with longitudinal ridges along the cuticle (Fig. 1, Fig. 2). This led us to the diagnosis of dirofilariasis.Fig. 2Section of the worm showing (a) two genital tubes, (b) the muscle layer, (c) detail of the cuticle with characteristic external longitudinal ridges (haematoxylin & eosin stain, ×400 magnification).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Dirofilariasis is a parasitic zoonosis due to nematodes of the Dirofilaria genus [[1]Capelli G. Genchi C. Baneth G. Bourdeau P. Brianti E. Cardoso L. et al.Recent advances on Dirofilaria repens in dogs and humans in Europe.Parasit Vectors. 2018; 11: 663Crossref PubMed Scopus (109) Google Scholar]. These worms are transmitted by many different mosquito species (Aedes, Culex, Anopheles, Mansonia, Culiseta, Simulium) to domestic and wild canids and, incidentally, to humans, that mostly represent a dead-end host [[2]Diaz J.H. Increasing risks of human dirofilariasis in travelers.J Travel Med. 2015; 22: 116-123Crossref PubMed Scopus (22) Google Scholar]. Dirofilaria immitis and Dirofilaria repens are the most frequently involved species. Human cases due to the former have been mostly reported in the USA. In contrast, D. repens is more cosmopolitan, and an increasing incidence of human cases is reported from southern European countries, especially Italy, where our patient may have been infected. In contrarst to D. immitis, which can be responsible for deep-organ infections, notably at the lungs and the heart levels, D. repens usually develops into a single subcutaneous nodule, mostly located in ocular and facial regions. The demonstration of longitudinal ridges along the cuticle ruled out D. immitis, and combined with the probable geographical area of contamination supported the identification of D. repens. Surgical removal of the nodule is the definitive and curative treatment of dirofilariasis. The authors declared that there are no conflicts of interest. No funding was received for this study. The following is the Supplementary data to this article: Download .jpg (.28 MB) Help with files Fig S1A sub-optimal (but unique) photograph of the nodule; subcutaneous nodule under the inferior eyelid (arrow). Obtained with the permission of the patient's daughter.