|Year : 2014 | Volume
| Issue : 1 | Page : 26-28
Microfilaria in thyroid aspirate-An unusual finding
Department of Pathology, Prathima Institute of Medical Sciences, Karimnagar, Andhra Pradesh, India
|Date of Web Publication||2-Jan-2014|
Department of Pathology, Prathima Institute of Medical Sciences, Karimnagar, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Filariasis is a major public health problem in tropical countries, including India. The disease is endemic all over India, especially in Uttar Pradesh, Bihar, Jharkhand, Andhra Pradesh, Orissa, Tamil Nadu, Kerala, and Gujarat. A majority of infected individuals in filarial endemic communities are asymptomatic. Adult worms live in the lymphatic vessels of the definitive host and microfilaria is released and circulates in the peripheral blood. Cases of microfilaremia have been reported from atypical sites like lymph node, pleural and pericardial fluid, breast lump, and bone marrow. We present a case of microfilaria in thyroid fine needle aspiration cytology, which is an unusual finding.
Keywords: Asymptomatic, microfilaria, thyroid aspirate cytology
|How to cite this article:|
Shastry S. Microfilaria in thyroid aspirate-An unusual finding. Thyroid Res Pract 2014;11:26-8
| Introduction|| |
Filariasis is a common public health problem in Southeast Asia. There are approximately 60 million people infected in the region and approximately 31 million people have clinical manifestation of this disease. Filariasis in India is caused by two closely related nematode worms-Wuchereria bancrofti and Brugia malayi.  The disease mainly involves the lymphatic system of the body. The most frequently involved lymphatics are those of lower limbs, retroperitoneal tissues, spermatic cord, epididymis, and mammary gland. ,
Although the incidence is high in the Indian sub-continent, yet it is unusual to find microfilaria on fine needle aspiration cytology (FNAC). We report an interesting case of microfilaria in solitary thyroid nodule of an euthyroid female patient.
| Case Report|| |
A 22-year-old female presented in the eye, nose, and throat (ENT) outpatient department with a solitary nodule on the left side of thyroid with a duration of 8 months. The size of the nodule was 4 × 3 cm and it was soft to firm, nontender and moved with deglutition [Figure 1]. The peripheral blood showed a total leukocyte count of 35000/μl and the differential leukocyte count showed 15% eosinophils. Erythrocyte sedimentation rate (ESR) was 22 mm in the first hour. Thyroid serology was normal. Ultrasonography (USG) diagnosed as thyroid adenoma. A clinical diagnosis of adenoma of the thyroid was made, and patient was sent for FNAC of the thyroid nodule. FNAC was performed using 10 ml disposable syringe and a 23-gauge needle. Hemotoxyllin and eosin and Giemsa stained smears revealed microfilariae of Wuchereria bancrofti along with few clusters of thyroid follicular cells with bland nuclear features, foam cells in a colloid mixed hemorrhagic background. Higher magnification revealed microfilariae with a clear space at the cephalic and caudal end [Figure 2]. A diagnosis of microfilariae of Wuchereria bancrofti in thyroid was made. Patient was advised diethyl carbamazine (DEC) and chlorpheniramine maleate for 21 days.
|Figure 2: Microfilaria of Wuchereria bancrofti with few follicular cells in background (H and E, ×10)|
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| Discussion|| |
Filariasis is transmitted by Culex mosquito and is caused by two closely related nematodes Wuchereria Bancrofti and Brugia malayi that are responsible for 90% and 10% cases, respectively, of the 90 million infections worldwide. Adult worms live in the lymphatic vessels of the definitive host and microfilaria is released and circulated in the peripheral blood. Filariasis causes a spectrum of diseases including asymptomatic microfilaremia, acute lymphangitis and lymphadenitis, chronic lymphadenitis, edema of limbs and genitalia and tropical pulmonary eosinophilia. 
Filariasis is endemic in India and Southeast Asia. Present estimate suggest that over 120 million people in 80 countries are affected by filariasis and more than 1.1 billion people live in areas where there is risk of infection. Despite the large number of people at risk and wide variety of tissues affected, it is unusual to find microﬁlariae in FNAC smears.
Individuals having circulating microfilariae are outwardly healthy but have the ability to transmit the infection to others through mosquito bites. Those with chronic filarial infection suffer severely from the disease but no longer transmit the infection.
Diagnosis of filarial infection is frequently made on clinical grounds in endemic areas, but demonstration of microfilariae in circulating blood is the only means by which one can make definitive diagnosis. 
In the present case, patient did not have any signs and symptoms of filarial infection, and the disease was not clinically suspected. FNAC of the thyroid swelling was done in aseptic conditions, by 23-gauge needle attached to 10 ml disposable syringe. Slides were air dried, fixed, with ether alcohol, and stained by hematoxylin and eosin and Giemsa.
The life cycle of Wuchereria bancrofti is found in two hosts. Man is definitive host and mosquito is an intermediate host. Adult worm resides in lymph node where the gravid female releases a large numbers of microfilariae. These larvae pass through the thoracic duct and pulmonary capillaries to the peripheral circulation.
Subsequent examination of night blood smear from patient failed to demonstrate microfilariae, which is in accordance with the reports by other authors thus suggesting that filaria can exist without microfilaremia. Majority of cases in endemic regions neither show microfilariae in blood, [Figure 2] and [Figure 3] nor any symptom.
|Figure 3: Microfilaria of Wuchereria bancrofti with few inflammatory cells in background. Note the cephalic and tail tip free from nuclei (Figure a and b, H and E ×40)|
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The main purpose of this case report is to raise the awareness that in tropical countries like India where filariasis is endemic, it should always be considered as a differential diagnosis of swelling at any site. Our presentation revealed that microfilaria may even be present at rare site like thyroid nodule. Careful examination of cytological smears is very important in prompt recognition of the disease and institution of specific treatment especially in unsuspected and asymptomatic cases. FNAC is extremely useful in identifying filarial infection at uncommon sites like thyroid.
| References|| |
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[Figure 1], [Figure 2], [Figure 3]