Abstract
Filariasis is a major concern, particularly in endemic regions. The majority of patients harbouring the parasite may remain asymptomatic for years. Here, we present six patients who were sent for routine cytological examination to rule out neoplastic pathology, in whom cytology identified filarial infestation. The main purposes of our paper are to highlight the importance of fine needle aspiration cytology (FNAC), a cheap and quick investigation to detect the microfilaria from tissue swelling and body fluids, and to point out that clinicians practising in endemic regions should always consider filarial infestation in patients presenting with longstanding swelling.
Introduction
Filariasis is a global health problem caused by nematodes, of which Wuchereria bancrofti is the main cause in > 90% of cases. 1 Despite its prevalence, detection of microfilariae by routine fine needle aspiration cytology (FNAC), smears and body fluid examination is infrequent. 2 We present a series of six cases where filarial infestation was confirmed on cytological examination when neoplastic pathology was suspected.
Case 1
A 35-year-old woman presented with a well-defined 3 cm × 2 cm firm swelling involving the left thyroid lobe for two years. An ultrasound suggested a solitary thyroid nodule. Cytology revealed small clusters and singly scattered thyroid follicular cells, some of which showed lymphocytic infiltrate on a background of thick colloid and haemorrhage. Many microfilariae were also seen scattered in the background (Figure 1a).
(a) FNA smear showing scattered thyroid follicular cells and sheathed microfilariae (arrow) (Papanicolaou staining, ×200). (b) Imprint smear showing scattered thyroid follicular cells and sheathed microfilariae (arrow) (Papanicolaou staining, ×200). (c) FNA smear showing many sheathed microfilariae (Papanicolaou staining, ×200). (d) FNA smear showing sheathed microfilariae (arrow) on a background of reactive lymphoid cell (Papanicolaou staining, ×100). (e) FNA smear showing scattered lymphoid cells and sheathed microfilariae (arrow) (Papanicolaou staining; 400 x). (f) Urine cytospin smear showing abundance of eosinophils (double arrows) and microfilariae single arrow) (Papanicolaou staining, ×200).
Case 2
Imprint cytology smears from a total thyroidectomy specimen removed from a 60-year-old male patient, whose preoperative ultrasound was suggestive of multinodular goitre, revealed a similar picture (Figure 1b).
Case 3
A 20-year-old man presented with a three-week history of two firm, non-tender subcutaneous swellings present. The larger swelling was in the left cubital fossa measuring 1 cm × 1 cm and the smaller was on the medial aspect of the left forearm measuring 0.5 cm × 0.5 cm. Cytology from both swellings revealed plenty of microfilariae on a clean fluid background (Figure 1c).
Case 4
A 60-year-old man presented with a one-year history of a 6 cm × 4 cm non-tender swelling involving the left temporo-parotid region. Multiple left cervical lymph nodes, each measuring 1 cm × 1 cm, were palpable. A computed tomography (CT) scan showed the mass to be lobulated and of soft-tissue density lesion with no bony erosion. Cytological smears from the left parotid area revealed a reactive population of lymphoid cells with a focal ill-formed granulomatous reaction and the presence of microfilariae (Figure 1d). Cytological smears from the left temporal area revealed clusters of basaloid cells having round to oval nuclei, and scanty to moderate cytoplasm; no definite atypia or mitotic activity was noted. Aspirate smears from the left cervical lymph nodes showed a reactive population of lymphoid cells.
Case 5
A four-year-old girl presented with a one-month history of a left inguinal swelling. Aspirate smears revealed microfilariae on a background of polymorphous lymphoid cells (Figure 1e).
Case 6
A urine sample from a 42-year-old woman had been submitted for cytology in the search for neoplastic cells. These were negative but revealed an abundance of eosinophils and microfilariae (Figure 1f).
Discussion
Filariasis may be divided into two types: lymphatic caused by Wuchereria bancrofti and Brugia malayi; and cutaneous or subcutaneous caused mostly by Onchocerca spp. and Loa loa. 1 Filarial parasites are largely confined to the tropical and subtropical regions of Southeast Asia. 2 The majority of infected persons remain asymptomatic for many years. Microfilariae may therefore be detected incidentally.
The most common mode of diagnosis of filariasis is through the demonstration of microfilariae in stained or unstained peripheral blood smears, and the detection of circulating filarial antigens. 4 Aspiration cytology is rarely performed for a routine diagnosis of filariasis. The various species of microfilariae may be morphologically differentiated by the presence or absence of a sheath and arrangement of nuclei at the tail tip. 5 Detection of microfilariae in these soft tissues is unusual, most being found in the lymph nodes, breasts and bone marrow, or in fluids such as bronchial aspirate, pleural or pericardial fluid, ovarian cyst or vaginal smears. 6 It is very uncommon to detect microfilariae in normal voided urine as in Case 6 of our series. A few cases of microfilariae in thyroid aspirates2–4,6 have been recorded, but very rarely in the salivary gland,6,7 subcutaneous tissue and in normally voided urine. 8 All six cases in our series showed sheathed microfilariae with the absence of a nuclei at the tail tip, thus confirming Wuchereria bancrofti infestation morphologically.
Limitations of the study
Our study is limited by the lack of distinction between filarial infestation and the actual disease of filariasis caused thereby. In our series, it was difficult to comment whether microfilariae were simply present as bystanders or actually causing disease. In Cases 3 and 5, it is likely that infestation was responsible for the disease state, but in others it was more likely incidental. Further retrospective search to calculate the real burden of filarial infestation was beyond the scope of this particular case series. It is also of note that cytology as a method for making specific diagnoses depends heavily on the skill and experience of the sampler and the cytologist.
Conclusion
Aspiration cytology is a cost-effective and rapid technique. Careful examination of cytological smears may detect microfilariae (and other pathogens) from uncommon sites and clinically unsuspected cases especially in endemic regions.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.