Microfilaria in thyroid aspirate - An unexpected finding.

Sir,

Lymphatic filariasis is a major health problem in tropical countries including India.[1] Due to the nocturnal periodicity of species endemic in India, it is difficult to find microfilariae in blood and fine-needle aspirates despite its high incidence in this zone. So far, about nine cases describing microfilaria in thyroid aspirates have been reported in literature.[2] We report this case of microfilaria in solitary thyroid nodule of a euthyroid female patient to emphasize the significance of careful screening of smears in endemic areas. In our case, the finding of microfilariae in thyroid aspirate was purely coincidental as there was no suggestive clinical history.

A 22-year-old female presented with a 2 cm × 2 cm non-tender, solitary nodule in front of the neck, which moved with deglutition for a duration of 6 months. Ultrasonography (USG) of the thyroid gland was done and thyroid serology was normal. A clinico-radiological diagnosis of a neoplastic lesion of the thyroid, possibly follicular neoplasm, was made and the patient was sent for fine needle aspiration cytology (FNAC) of the thyroid nodule. Papanicolaou and Giemsa stained smears revealed microfilariae along with clusters of thyroid follicular cells, cyst macrophage against a background of scanty thin colloid [Figure 1]. Higher magnification revealed microfilariae with a clear space at the cephalic and caudal ends. So, a diagnosis of microfilariae of Wuchereria bancrofti in thyroid was made.

Figure 1

Cytology smear from thyroid aspirate showing microfilaria against a background of thyroid follicular cells, cyst macrophage and colloid (MGG, ×100)

The peripheral blood showed a total leucocyte count of 18,000/μL and a differential leucocyte count (DLC) of 20% eosinophils. The absolute eosinophil count was 3600/μL. The patient was advised diethyl carbamazine (DEC 6 mg/kg body weight daily) along with antipyretics and antihistaminics for 12 days. This cycle was repeated for another period of 12 days. The patient responded to the treatment and the nodule disappeared by the end of 3 months.

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.[3] 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, bone marrow, bronchial aspirate, ovarian cyst fluid, cervicovaginal smears and thyroid.[4] Our case is unique in that the patient presented with solitary thyroid nodule, which showed microfilaria on FNAC similar to the cases reported by Chowdhury et al.[2] In the present case, the patient was an asymptomatic carrier with larvae present in microvasculature of thyroid gland. As proposed by Chowdhury et al.,[2] a possible rupture of vessels may have led to hemorrhage and release of microfilaria in the thyroid and the subsequent histiocytic reaction which resulted in the development of a solitary thyroid nodule. This case is worthy of note because clinico-radiologically the patient was suspected to have a neoplastic lesion, but the aspirate demonstrated microfilaria. A simple inexpensive procedure like FNAC thus averted the need for surgery.