Paramassetric Subcutaneous Dirofilariasis: A Rare Entity

Abstract

Dirofilariasis is an uncommon zoonotic parasitic infection affecting humans due to the bite of a mosquito vector. It is an endemic caused by Dirofilaria which is characterized in humans as nodules in lungs, subcutaneous tissue, peritoneal cavity, eyes. We present a case of Dirofilariasis with subcutaneous presentation in paramassetric region.

Introduction

Dirofilariasis is a zoonotic infection caused by a helminthic nematode belonging to the genus Dirofilarae. They usually occur as habitual parasites of canines. Although rare, humans have been reported to serve as end hosts for these parasites. The parasitic infection is usually transmitted by an intermediate host mosquito vector belonging to the genre Ades, Anopheles or Culex [1].

There are about 40 variants of Dirofilarial species identified, among which six are known to cause infection in humans. D. repens, D. ursi, D. tenuis and D. striata are found in the subcutaneous tissue where as D. immitis and D. spectrum are found in the pulmonary and vascular spaces [2]. The species causing the subcutaneous infection tends to show geographical variation, where the D. repens is reported to be found commonly in Asia.

In India majority of the cases have been reported from the southern state Kerala [3, 4]. We report a case of an elderly female with subcutaneous Dirofilariasis in the paramassetric region.

Case Report

A 50 year old female hailing from Malappuram district, Kerala presented with a painless nodular swelling on the left cheek in the inferior paramassetric region of one month duration which was insidious in onset and gradually increasing. Clinical examination revealed a firm, oval swelling in the left cheek measuring 2 cm × 1 cm, which was freely mobile. The skin and the mucosa overlying the swelling were normal in appearance. The systemic examination was non remarkable and the patient was unable to recall any injury or insect bite to the face. No regional lymph node enlargement was detected (Fig. 1a).

Fig. 1.

a Pre op photo showing the swelling with planned Incision Marking. b Ultrasonography indicating the presence of a live worm

An ultra-sonographic examination revealed an oval cystic lesion in the left side of the face superficial to masseter muscle with curvilinear echogenic areas suggestive of live worms (Fig. 1b).

A differential diagnosis of cysticercosis was made. Routine hematological examination revealed no abnormality.

A decision was taken to surgically excise the lesion via an extraoral approach. The lesion was excised in toto keeping the nodule intact (Fig. 2a) and was sent for examination to the Department of Microbiology. The dissected nodule revealed a clear viscous fluid and a live worm which was thin cylindrical, white, 0.5 mm thick and 40 mm in length. The anterior end was rounded and had greater diameter than of posterior end (Fig. 2b). Microscopic examination of the worm showed multiple transverse sections of adult filarial worm with outer multilayered cuticle containing external ridges, hypodermis, lateral chords and a well-developed inner muscular layer lining a pseudocoele cavity which were characteristic of the Dirofilarial worm [5].

Fig. 2.

a Excised Specimen sectioned and showing the worm. b Microscopic image of the nematode

The extraoral wound was closed by subcuticular suturing for a more esthetic outcome. The site of surgery healed uneventfully and on follow up no residual lesion was found.

Discussion

Dirofilariasis is a zoonotic parasitic infection rarely affecting humans caused by a nematode belonging to the genus Dirofilaria. Dogs, Monkeys and Cats comprises the primary host and mosquitoes such as Mansonia uniformis, Mansonia annulifera, and Ades aegypti are the potential vectors [6]. Dilofilariasis in humans is commonly presented as pulmonary dilofilariasis casused by D. immitis and subcutaneous variant caused by D. tenuis and D. repens.

Subcutaneous nodules are seen more often in the ocular region, conjunctiva and left cheek. Intraorally, buccal mucosa and lower lip have more predilection to the lesion. Once transmitted to the human hosts these nematodes mature within the subcutaneous nodule in a span of 6 months. But they tend to die before the stage where they could produce microfilariae, hence these patients will have no microfilariae in peripheral smear [7].

The disease is said to be commonly encountered in the 4th to 5th decade of life while showing significant female predilection. Significant geographical variation was observed as an endemic in India and Sri Lanka other than Africa, Asia, Australia, Europe, and America [8].

In our case the patient was presented with an insidious, painless, mobile subcutaneous nodular swelling of one month duration in the paramassetric region. Provisional diagnosis was that it could be a tubercular lymphnode or an adenoma from parotid. Ultrasonography revealed hypoechoic regions containing live worm which led to the conclusion that it could be cysticercosis. Routine blood investigation did not reveal any significant findings.

An extraoral incision was placed over the swelling and the subcutaneous nodule was exposed and resected. Dilofilariasis was confirmed by dissection and analysis of the specimen which revealed a 40 mm long single D. repens worm.

The differentiation among the species is done based on the size and the features of the body wall. The key features useful in the identification of D. repens are longitudinal ridges separated by a distance wider than the ridge itself, 95–105 ridges on the circumference of the body and 2–5 chord nuclei in each cross section of worm [9].

In this case the surgical resection has preserved the entire morphology of the worm hence identification was easy. Post surgical days were uneventful and the healing was satisfactory. Human Dirofilariasis is caused by a single worm and usually there is no microfilariae in the peripheral blood. Hence the excision is usually curative and no further treatment is needed.