Cytological findings of microfilariae in different sites: A retrospective review of 22 cases from endemic region.

BACKGROUND: Filariasis is a major health problem in India. Despite the high prevalence, microfilariae are rarely found in cytology smears. Most of the cases are incidentally found, solely or in association with other pathologies. AIMS AND
OBJECTIVES: The study was undertaken to analyze the prevalence and cytology findings of cases of incidentally found microfilariae in cytology smears (fine-needle aspiration cytology [FNAC]/body fluids) from different body parts.
MATERIALS AND METHODS: This was a retrospective study over 5 years, where the cases of microfilariae in aspirates from swelling of different locations and body fluids were reviewed, and clinic-pathological data were analyzed. RESULTS AND ANALYSIS: Out of 16,738 cases of FNAC and 882 cases of fluid cytology, 22 cases (0.124%) of incidental finding of microfilaria were documented in cytology smears. The cases were diagnosed from lymph nodes (5 cases), skin and soft tissue (4 cases), scrotal (4 cases), breast (3 cases), thyroid (2 cases), and pleural fluid (2 cases). We found eosinophilia in 15 cases (68.18%) of filarial lesions. We found two cases of incidental findings of microfilariae in association with malignant lesions.
CONCLUSION: Filariasis should be considered as differential diagnosis of swelling of lymph nodes, skin, soft tissue, inguinoscrotal region, and other sites as well. Careful screening of cytology smears may help in detection of incidental cases in the association of other pathologies.

INTRODUCTION

Filariasis is a major parasitic disease in many tropical and subtropical countries.[12] It is endemic in India, especially in the states of Bihar, Jharkhand, West Bengal, Uttar Pradesh, Orissa, Kerala, and Gujarat.[1] Lymphatic filariasis is increasing every year and over 553.7 million people are at risk of lymphatic filariasis in India.[13] Conventional diagnosis of filariasis depends on the demonstration of microfilaria in peripheral blood smears. Despite the high incidence and prevalence, microfilariae are rarely found in cytology smears of fine-needle aspiration cytology (FNAC) and body fluid.[1] Most of the previous literatures revealed an incidental diagnosis of microfilariae in cytology smears of different locations including breast, thyroid, soft tissue, lymph nodes, salivary glands, and effusion fluids.[24] The present study was undertaken to analyze the cases of incidentally found microfilariae in cytology smears (FNAC/body fluids) from different body parts.

MATERIALS AND METHODS

The retrospective study was conducted over 5 years (January 2011 to December 2015) in a tertiary care hospital in rural India. We collected the cases retrospectively from our cytology records (FNAC/body fluids), and cases are reevaluated and analyzed. During the study period, a total number of 16,738 cases of FNAC and 882 cases of fluid cytology were examined in our cytology department. FNAC was done using 22–23 gauge needle attached with 10 cc syringe. Air-dried smears were stained with Leishman-Giemsa stain and alcohol-fixed smears were stained with Papanicolaou stain. The aspirated fluids were centrifuged, and smears were prepared from centrifuged deposits. We found (22) cases of microfilariae cases in aspirates from swelling of different locations and body fluids. The cases were reviewed and clinic-pathological data were analyzed.

RESULT

We have analyzed 16,738 cases of FNAC and 882 cases of fluid cytology which were undergone during the period of 5 years (January 2011–December 2015). We found 22 cases (0.124%) of incidental finding of microfilaria in cytology smears. Age distribution of the cases showed a wide age range from 18 to 62 years with a mean age of 37.95 years. Most common age group was 31–40 years (9 cases: 40.9%) followed by 21–30 years (5 cases, 22.72%) [Figure 1]. Sex ratio revealed slight male predominance (male:female ratio: 1.2:1). The most common site of aspiration was lymph node (5 cases, 22.72%). Site distribution of the cases is shown in Table 1. We found microfilaria in two cases of microfilariae in pleural fluid in pleural fluid cytology, two cases in thyroid aspirates, one from parotid gland aspirate, and one from gallbladder lump. Most frequent clinical presentation of the cases was swelling (59.09%). Pain (6 cases, 27.27%), erythema (2 cases, 9.09%), and fever (1 case, 4.54%) were less frequent manifestations. In most of the cases, aspirates were blood mixed (12 cases, 54.54%) and fluid (8 cases, 36.36%). In two cases, aspiration was greasy. We found three cases of incidental finding of microfilariae in association with malignancy. The cases were microfilariae in association with gallbladder carcinoma, mucoepidermoid carcinoma of parotid, and in a malignant pleural effusion from breast carcinoma. Peripheral blood smears revealed eosinophilia in 15 cases (68.18%) and microfilariae were seen in phosphate buffered saline of one case. Microscopical examination of the lymph node aspirates showed sheathed microfilariae of Wuchereria bancrofti in the background of reactive lymphoid cells and eosinophils [Figure 2].

Figure 1

Bar diagram showing age distribution of the cases of filariasis in cytology smears

Table 1

Distribution of clinic-cytological features of cases of microfilarial lesion

Figure 2

Cytology of inguinal lymph node showing microfilaria of Wuchereria bancrofti in the background of reactive lymphoid cells population (Leishman and Giemsa stain, ×40)

Cytology of the breast swellings revealed sheathed microfilariae of W. bancrofti. In one case, it was associated with acute inflammatory reaction (neutrophils and macrophages) [Figure 3], and in one case, it was associated with fibroadenosis. Cytology of centrifuged deposit of aspirated fluid from four scrotal swelling (two epididymal nodules and two hydrocele fluid) showed sheathed microfilariae of W. bancrofti with eosinophils, occasional lymphocytes in a proteinaceous background. Among the four subcutaneous swelling, all showed mixed inflammatory cell background and necrotic granular debris along with microfilariae. Cytology of both the thyroid swelling showed cytology of nodular colloid goiter associated with incidental findings of sheathed microfilariae of W. bancrofti. Granulomas (epithelioid/histiocytic) were associated with three cases (one case each from breast, soft tissue, and lymph node).

Figure 3

Cytology of breast swelling showing many coiled microfilariae in the background of polymorphous inflammatory cells (Leishnam and Giemsa stain, ×40)

DISCUSSION

Filariasis is a major health problem in many tropical countries including India.[15] In India, most of the filariasis is caused by W. bancrofti (95%) and Brugia malayi (5%).[256] Most commonly affected organs are lymphatics of lower limbs, retroperitoneal tissue, spermatic cord, epididymis, and breast.[45] Adult worms of filarial involve the lymphatics and microfilariae are released in peripheral blood. Most of the filariasis cases are asymptomatic but clinically present with lymphangitis, edema of the limbs and genitalia, and eosinophilia. In endemic region, human beings are affected in early life, and peak manifestations are found in 15–20 years.[12] Despite high incidence of filariasis in the Indian subcontinent, finding of microfilaria in cytology smears is unusual and incidental.[12]

During the study period of 5 years, we found 22 cases (0.125%) of incidental findings of microfilariae. Khare et al. found twenty cases (0.078% of total FNAC) of microfilariae in their study. We found a large number of cases among 31–40 years (9 cases, 40.9%) and 21–30 years (5 cases, 20.72%) age group. Our findings were consistent with the findings of Andola and Naik and Khare et al.[25] Majority of the cases in the present study presented with swelling (20 cases, 90.90%) and filariasis was not considered as differential diagnosis. Similar findings were seen in the studies of Andola and Naik (72%), Khare et al. (100%), and Mitra et al. (95.83%). We found lymph nodes as the most common site of incidental finding of microfilaria in our study (5 cases, 22.72%), similar to Andola and Naik (28%).[2] However, Mitra et al. found breast as the most common site (8 cases, 33%) and Khare et al. found testiculoscrotal and lymph nodes as common sites of involvement in their series.[15] Yenkeshwar et al. found soft tissue as the most common site of incidental finding of microfilaria in their series (7 cases, 31.8%). We think the cause of such discrepancy is not properly understood, but almost all the series are based on a small number of cases.

Smears from the lymph nodes revealed microfilariae in the background of reactive lymphoid cells (centroblasts, centrocytes, and mature lymphocytes) and eosinophils, similar to the findings of others [Figure 2].[457] We found four cases of microfilariae in scrotal swelling. Two cases were presented with epididymal nodule and other two cases were found from hydrocele fluid. Khare et al. found microfilariae in 12% of testiculoscrotal swelling. Most common presentation of filariasis in India is epididymo-orchitis because of blockade of lymphatic vessels of the spermatic cord is the most common site of involvement by microfilariae even in cases of asymptomatic filariasis.[6] Many cases of adult filarial parasites were reported from testiculoscrotal swelling.[58]

Many authors have reported incidental finding of microfilaria in breast aspirates, but breast is relative uncommon site.[1910] We found three cases of microfilariae in breast aspirates. In two cases, microfilariae were found incidentally with cytology of fibroadenosis, but in one case, the cytology revealed plenty of microfilariae of W. bancrofti mixed with acute and chronic inflammatory cells, occasion granulomas in the smears [Figure 3].

Thyroid is also very uncommon site for microfilaria. We found two cases of incidental finding with colloid and thyroid follicular cells similar to the finding of Mitra et al. and Varghese et al.[111]

We found two cases of microfilariae in pleural fluid cytology. In one case, there were multiple microfilariae in a proteinaceous background with lymphocytes and eosinophils. Another case was pleural effusion in a treated case of breast carcinoma. Cytology of pleural fluid showed the presence of microfilariae without the presence of any malignant cells [Figure 4].

Figure 4

Cytology of hemorrhagic pleural effusion showing multiple microfilariae of Wuchereria bancrofti in the background of Red blood cells (Papanicolaou stain, ×40)

Incidence of microfilarial lesion in soft tissue and skin swelling is uncommon.[457] However, individual cases and case series have been reported in different previous literatures.[45712] We found four cases in our series. We found two cases of microfilariae in association with malignancy. One case was incidental finding of microfilaria of W. bancrofti in cytology of gallbladder carcinoma and another was in association with mucoepidermoid carcinoma of parotid gland. Coexistence of microfilaria in association with malignancy has been reported by many previous authors.[1314] Presence of microfilaria within a neoplasm is a chance association. However, increased vascularity and lymphatics in a malignancy cause increased concentration of microfilariae at the local site in a previously affected person. Lymphatic or vascular blockade results rupture of vessels and release of microfilariae at the local site.[213] Finding of microfilariae in other tissue sites as a “dead end” site is also explained as aberrant migration due to local factors such as lymphatic blockage and damage of vessel wall by inflammation, stasis, and trauma.[2415]

We found eosinophilia in 15 cases (68.18%) and presence of microfilariae in one case (4.54%). Prevalence of eosinophilia is high in the present study in comparison to Mitra et al. (33.33%) and Khare et al. (35%). However, incidence of microfilariae in peripheral blood is low in comparison to others.[15]

CONCLUSION

Diagnosis of filariasis should be considered as differential diagnosis of swelling of skin, soft tissue, inguinoscrotal region, and other sites as well. Careful screening of all slides will be helpful to detect the incidental presence of microfilaria, even in asymptomatic patients and chance of associated finding with other pathologies.

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Conflicts of interest

There are no conflicts of interest.