Role of fine needle aspiration cytology in diagnosing filarial arm cysts

Abstract

Filariasis is prevalent in tropical and subtropical areas and is endemic in regions of India. Lymphatic filariasis in India is caused mainly by two species of nematodes: Wuchereria bancrofti and Brugia malayi, which invade the human lymphatic system. We report two cases of superficial cystic lesions of the upper limb revealed on fine needle aspiration (FNA) to be clinically unsuspected filariasis. Despite similar aetiologies, both cases revealed variations in aspirate nature, smear morphology and peripheral blood findings. FNA provides definitive diagnosis and is an important tool for diagnosing soft tissue swellings owing to filariasis.

Background

Filariasis has wide distribution in the tropical and subtropical regions and is endemic in India, China, Indonesia, parts of Asia and Africa. Two closely related nematode worms, Wuchereria bancrofti and Brugia malayi mainly cause filariasis in the Asian subcontinent. South Asian Bancroftian filariasis is transmitted by the Culex mosquito while Brugian infections are transmitted by Mansonia species.^{1 2} The adult filarial worms reside in the lymphatic system from where the gravid female releases large number of microfilaria which may pass through the thoracic duct and pulmonary capillaries into the peripheral blood and occasionally microfilaraemia may be found in the infected patient. Most frequently, the lymphatic system of the lower limbs, retroperitoneal tissues, spermatic cord, epididymis and mammary glands is involved.^3–5

We encountered two unusual cases of filarial infestation as solitary cystic swelling of arm subcutaneous tissue. Exact incidence of microfilaria presenting as upper arm cystic swelling is not known but filarial cystic swelling in the upper arm is very rare.^{5 6} We are reporting these cases to highlight the definitive role of simple, cost-effective fine needle aspiration (FNA) technique for microfilaria detection in filariasis endemic regions.

Case presentation

Case 1

A 35-year-old woman, resident of Behraich (Uttar Pradesh) presented with a painless, arm soft tissue swelling gradually increasing over a period of 2 months. She had no other systemic complaints. Examination revealed a solitary, non-tender, mobile, soft cystic swelling measuring 1.5×1.5 cm on ventral surface of the left arm. There was no axillary lymphadenopathy.

Case 2

A 38-year-old man, resident of Lucknow (Uttar Pradesh) had painful swelling in left arm with a 1 month history of low-grade, off and on fever. Examination revealed a non-mobile, tender, firm swelling measuring 2×0.5 cm arising from a cord like structure on the medial side of upper left arm. No evidence of lymphadenopathy was present.

Investigations

Case 1

FNA (21G) from the arm swelling yielded aspirate of 0.3 ml clear fluid. Swelling shrunk in size following aspiration. H&E stained smears revealed curved microfilarial sheaths and occasional eosinophils, lymphocytes against proteinaceous background (figure 1). Peripheral blood smear did not show microfilariae or eosinophilia.

Figure 1.

Photomicrograph from case 1 showing slightly curved sheath of microfilaria with an eosinophil and lymphocyte on proteinaceous background (H&E ×400).

Case 2

White chylous fluid was aspirated. FNA smears showed a mixed inflammatory infiltrate comprising eosinophils, neutrophils and a few histiocytes along with foreign body giant cells. Numerous microfilariae of W bancrofti with characteristic cytomorphology of sheathed larvae with tail-tip free from nuclei were identified (figures 2 and 3). At the time of aspiration, chylous fluid had raised suspicion for parasitic lymphatic involvement and the wet smear prepared showed actively motile larvae. Peripheral blood smear showed eosinophilia with absolute eosinophil count of 0.98×10⁹/l (reference range 0.04–0.44×10⁹/l). No microfilariae were seen on the blood film.

Figure 2.

Scanner view from case 2 showing tangled microfilariae with dense mixed inflammatory infiltrate (H&E ×100).

Figure 3.

Photomicrograph from case 2 showing microfilaria of Wuchereria bancrofti with characteristic cytomorphology of sheathed larvae with tail-tip free from nuclei. Mixed inflammatory infiltrate composed of eosinophils and neutrophils is seen in the background. (H&E ×400).

Discussion

Lymphatic vessels of the definitive host (man) harbour the adult worms of W bancrofti and B malayi and microfilaria are released in the peripheral blood. Majority of filarial infections are asymptomatic in endemic areas like eastern part of Uttar Pradesh; although the disease can manifest as asymptomatic microfilaraemia, acute lymphangitis and lymphadenitis, chronic lymphadenitis, oedema of limbs and tropical pulmonary eosinophilia.^7–10 The clinical picture in the present cases did not give any clue regarding the aetiology.

Microfilariae have been reported at various sites like epididymis,¹¹ breast,¹² urine,¹³ thyroid,¹⁴ ovarian fluid,¹⁵ bone marrow¹⁶ and upper arm cystic swelling.⁵ Cases often present with lymphatic system involvement, but the extralymphatic compartment can also get involved. Extravasation may explain the presence of microfilariae in pericardial fluid, breast cyst fluid and bronchial aspirate. The parasites circulate in lymphatic and vascular compartments but the presence of filarial organism in tissue fluids and exfoliated surface material probably occurs owing to conditions causing lymphovascular obstruction resulting in extravasations of blood and release of microfilariae.^{17 18} Such aberrant migration to these dead end sites is probably determined by local factors, such as lymphatic blockage by scars or tumours and damage to the vessel wall by inflammation, trauma or stasis. Our patients were asymptomatic amicrofilaraemic carriers residing in filariasis endemic region of North India. Rupture of vessels may have led to release of microfilariae into the subcutaneous tissue. Surrounding host tissue reaction probably led to the development of a well-defined cystic swelling containing multiple microfilariae. Filariasis rarely presents as cystic swelling.^{5 6 9 17 18} Eosinophilia resulting from filariasis may be attributed erroneously to coexistent pathologies.¹⁶

The difference in the swelling type (nodular vs thickened cord like) and nature of aspirates (clear vs chylous) could be owing to extravasation in the first case. Findings of the two cases also varied with respect to peripheral eosinophilia and FNA smear, that is, microfilarial morphology and the associated inflammatory response. Peripheral blood smear examination is a useful but relatively less sensitive tool to diagnose filariasis. Eosinophilia, although relatively common, is non-specific and, as in case 2, is not invariable.^{3 4 10} Cellular background of granulocytes and giant cells in the second case versus clean background of the first case may be the result of host tissue response owing to lymphatics involved. The cytology of the filarial infestation can reveal microfilaria with or without adult worms and associated eosinophils, neutrophils and mononuclear cells.^{12 13 17–19} Our cases did not have the presence of either ova or adult worm in aspirates. Our report of clinically unsuspected filariasis supplements prior literature on unusual presentations of this parasite and reminds the tropical pathologist to maintain a high index of suspicion for unusual infections at uncommon sites.²⁰

Learning points.

• Filariasis may present as cystic lesions in unusual sites without associated lymphatic involvement in the form of lymphangitis and lymphadenitis.

• Fine needle aspiration represents a minimally invasive, cost-effective and definitive diagnostic modality for diagnosis of filarial soft tissue swellings.

• The type of aspirate and the cytological findings including the nature of the inflammatory response are variable and may depend on location of the parasite (lymphatic vs extralymphatic), local trauma, lymphatic obstruction and stasis.