Microfilariae coexisting with a follicular lesion in thyroid aspirate smears in an uncommon case of a retrosternal thyroid mass, clinically presenting as malignancy

To the Editor, Filarial infection is a public health problem in the tropical regions of South-east Asia, including the Indian subcontinent that includes certain areas of heavy infestation, like Madhya Pradesh, Bihar, Jharkhand, along with others. It is caused by the nematodes Wuchereria bancrofti, Brugia malayi, Brugia tumori and others, transmitted through a mosquito Culex fastigens. Its disease manifestations include lymphoedema and superficial swellings.[1–3] Varied sites of involvement documented on aspirate smears include breast, epididymis, spermatic cord, lungs, etc.[4–6] Over the years, it has been uncommonly identified in the thyroid.[7–13] Herein, we present an uncommon case of a retrosternal thyroid mass that clinically presented as malignancy and on aspiration cytology disclosed a follicular lesion with coexisting microfilariae. A 55-year-old gentleman from Ranchi (Jharkhand, India) was referred to our hospital with complaints of anterior neck swelling since 2 months, associated with dysphagia to solids and alteration of voice for a month. He had been a tobacco chewer for 30 years. He also disclosed history of aspiration a month ago, along with breathlessness. On clinical examination, his general condition was good. On local examination, a soft swelling was noted over his right thyroid and isthmus and a 10×7 cm hard swelling was noted over his left thyroid, extending into the retro sternum that did not move with deglutition. Left vocal cord palsy was noted. There was no stridor. Clinically, he was presumed with a diagnosis of stage IV carcinoma thyroid. He underwent laboratory and radiological investigations, including an outside computed tomography (CT) scan, followed by fine-needle aspiration cytology (FNAC) on three occasions, including twice at our hospital. His hemoglobin was normal i.e. 12 gm/dl (Normal: 13-17 gm/dl). Total leukocyte count was high i.e., 13.7×10e9/L (Normal: 4-10×10e9/L), including absolute neutrophilia. Percentage and absolute eosinophil counts were normal 4.73% and 0.65×10e9/L (Normal: 1-6% and 0.2-1×10e9/L). Basophil percentage was marginally high i.e., 0.33% (Normal: 0-0.2%). His thyroid function tests were within normal limits. There was no access for thyroid scan results. Limited accessible imaging findings included a CT scan report that disclosed a left thyroid lobe lesion, eroding the thyroid cartilage, trachea and thoracic inlet. His chest X-ray was normal. FNAC was performed by multiple passes in the thyroid using a 23-gauge needle. Smears were fixed in alcohol stained with Papanicolaou (Pap), while air-dried smears were stained with Giemsa stain. The initial smears were reported as papillary carcinoma thyroid. Repeat smears were hypercellular, comprising benign appearing follicular cells in focal acinar formations, flat monolayered sheets and focal papillaroid arrangements, lacking anatomical edge. Cells exhibited focal nuclear overlapping, focal grooves and fine chromatin clearing in rare cells. No nuclear elongation, uniform nucleomegaly or intranuclear inclusions were noted within the hypercellular smears. Besides, there were sheets of cystic macrophages and Hurthle cells in a background of thick and thin colloid. Diagnosis of an atypical follicular lesion of undetermined significance was considered. On critical examination, microfilariae of W. bancrofti were identified that displayed presence of sheath and were deficient in somatic nuclei at the posterior end of the body that was curved. A few rhomboid-shaped Charcot Leyden (CL) crystals were noted. There were no inflammatory cells. The previous smears were reviewed and a final diagnosis of microfilarial infestation, along with follicular lesion (of undetermined significance) was offered. [Figure ​[Figure1a1a–e] Figure 1 a) Hypercellular smear showing clusters of follicular cells. Pap stain ×100; b) Follicular cells with surrounding macrophages. Pap stain ×400; c) Cells showing focal nuclear overlapping. Pap stain ×1000; d) Flat monolayered sheet ... Following, the patient succumbed to death within a week. However, post-mortem examination could not be performed.