Subcutaneous filariasis: An unusual presentation with an adult gravid worm on aspiration.

Detection of adult gravid filarial worm in fine-needle aspiration cytology (FNAC) smears is unusual despite the high incidence of this parasite in endemic zones. Bancroftian filariasis presenting as subcutaneous nodules is very rare, and only a few cases are reported in literature. In spite of various reports stating the presence of microfilaria using aspiration cytology in various sites, the presence of an adult gravid filarial worm in subcutaneous nodules by FNAC is an extremely rare finding. We hereby report an unusual case of detection of adult gravid worm of Wuchereria bancrofti on FNAC of a subcutaneous nodule in the axilla. In differential diagnosis of subcutaneous nodular swellings, a possibility of filariasis must be kept in mind, and a careful search should be done for the adult worm or microfilaria in the aspiration smears done for an accurate diagnosis. The conventional method of diagnosis of filariasis is by demonstration of microfilaria in the peripheral blood smear which may be diurnal or nocturnal. Buffy coat can be helpful in detecting microfilaria in asymptomatic cases with peripheral blood eosinophilia.

INTRODUCTION

Filariasis is an endemic disease in tropical countries of Africa, Southern America, and Asia where it is regarded as major public health problem. Out of the eight species of filarial worm which infects humans, Wuchereria bancrofti and Brugia malayi are responsible for most of the cases in India.[1]

The most common presentations of W. bancrofti infestation are elephantiasis, chronic lymphedema, epididymitis, funiculitis, and lymphadenitis.[2] Unilateral axillary swelling is an extremely uncommon presentation of bancroftian filariasis even in endemic areas.[234] In contrast to W. bancrofti, Loa loa commonly presents as a subcutaneous nodule.[5] We report such a case of subcutaneous filariasis presenting as an axillary swelling caused by W. bancrofti, diagnosed by fine-needle aspiration cytology (FNAC).

CASE REPORT

A 22-year-old male resident of Eastern Uttar Pradesh presented with swelling in the right axilla for 2 months. There were no constitutional symptoms such as fever, cough, or weakness. On examination, a firm, nontender, 2 cm × 1 cm subcutaneous swelling was noted in the right axilla [Figure 1]. No other axillary, cervical, or inguinal swelling was noted. A clinical diagnosis of the right axillary lymphadenopathy was made. On aspiration, the swelling yielded clear fluid with a white thread-like structure. Smear showed adult gravid female filarial worm measuring 3 cm in length having an intact outer cuticle layer and body cavity containing embryonated eggs and different stages of developing microfilaria [Figure 2]. In addition, scattered coiled and straight larvae of W. bancrofti were seen which were sheathed and had no nuclei in the tail end [Figure 3]. The background was clean, and no inflammatory cells were seen. On further examination of the patient, the mild right scrotal swelling was noticed, and an FNAC was performed. Smears showed findings suggestive of epididymitis with occasional coiled larvae of W. bancrofti. Ultrasound-guided examination of the axillary swelling revealed an oval cystic lesion in subcutaneous plane of the right axilla with echogenic dancing larva sign, suggestive of filariasis. Laboratory examination of blood revealed Hb of 12.6 g/dl and normal white blood cell count (total leukocyte count-4000/cmm); differential count showed eosinophilia with 33% eosinophils, angiotensin-converting enzyme-2500/cmm, and erythrocyte sedimentation rate of 34 mm at the end of the 1st h. The daytime peripheral blood smear examination did not reveal any microfilaria. However, buffy coat preparation showed microfilaria of W. bancrofti. The patient was treated with diethylcarbazine for 21 days which is the drug of choice for bancroftian filariasis. The axillary swelling reduced in size, and the scrotal swelling disappeared after treatment.

Figure 1

Right axillary subcutaneous swelling measuring 2 cm × 1 cm

Figure 2

Fine-needle aspiration cytology showing coiled up adult gravid female worm with outer cuticle layer and body cavity containing embryonated eggs and different stages of developing microfilaria (Giemsa, ×10)

Figure 3

Fine-needle aspiration cytology showing unsheathed microfilariae of Wuchereria bancrofti with nuclei not reaching up to the tail end (Giemsa, ×10)

DISCUSSION

Filariasis may produce acute as well as chronic clinical manifestations, or a person may remain asymptomatic in endemic areas.[5] Clinically, filariasis can be of two major categories – filariasis of skin and subcutaneous tissue and lymphatic filariasis. Onchocerca volvulus and L. loa are the most common organisms reported in former, and W. bancrofti and B. malayi are the two most common species in the latter. W. bancrofti has been detected by FNAC at different sites such as breast, thyroid, lymph node, liver, and lungs, and a small number of cases have been reported in the bone marrow and body fluids; however, a subcutaneous nodule is a very rare presentation.[267] This was seen in our index case where the species was confirmed by the presence of sheathed microfilaria and the absence of nuclei in tail end.

There are reports in literature showing the presence of microfilaria on FNAC in various sites such as spermatic cord, epididymis, testis, retroperitoneum, soft tissue, and breast; however, reports of adult worms in cytological aspirates are sparse.[7] Pandit et al.[8] and Azad et al.[2] have reported the presence of adult filarial worms in soft-tissue swelling. Satpathi et al.[9] and Chakrabarti et al.[7] have reported rare cases of adult filarial worms in the breast aspirate. Thus, barring a few reports, the presence of an adult gravid filarial worm on FNAC is an extremely rare finding.

In the past, the definitive diagnosis of filariasis has been based on an identification of the microfilaria in blood. The microfilaria of W. bancrofti often demonstrates periodicity, and the blood samples must be taken at night, preferably between 10 p.m. and 2 a.m. A review of 18 cases of filariasis diagnosed on FNAC revealed that only 2 (12%) were positive for microfilaria on blood examination.[10] Thus, because of the low yield and stringent sampling requirements of a blood examination, the preparation of buffy coat smear can detect the parasite in asymptomatic cases presenting with eosinophilia in endemic areas as was seen in our case.

Filariasis should be considered one of the differential diagnoses in patients presenting with subcutaneous nodules in filarial endemic zones. FNAC of these nodules can be really helpful in such cases, and an awareness and active search for an adult worm or microfilaria should be done for an accurate diagnosis.

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Conflicts of interest

There are no conflicts of interest.