Microfilariae in thyroid aspiration smear--an unexpected finding

Microfilaria in a thyroid nodule discovered by fine needle aspiration cytology

Filariasis is a major health problem in tropical countries, including India. The disease is endemic all over India, especially in Uttar Pradesh, Andhra Pradesh, Orissa, Bihar, Jharkhand, Tamil Nadu, Kerala, and Gujarat. A heavy parasitic load may appear in the blood, urine with chyle, and at times in scrotal aspirates. It is very unusual to find microfilaria in thyroid aspirate. Here, we present a rare case in which microfilaria was found during fine needle aspiration cytology of a solitary thyroid nodule.

Standard karyotyping concentrates microfilaria and can be a valid concentrating technique for their detection

During karyotype preparation from the bone marrow aspirates of 209 haematological malignancy cases, microfilaria were detected in four samples, whereas routine marrow and peripheral blood smears of these four cases did not show any parasite. The patients were recalled, and their peripheral blood was processed by karyotyping and standard concentration techniques. Karyotype preparation from peripheral blood was performed with and without addition of colchicine. When the blood was processed for karyotyping with colchicine, microfilaria were detected in the peripheral blood of all four patients. In samples without added colchicine, no parasite was observed. The same samples were processed by Knott's concentration technique, which showed microfilariae only in one of the four patients. Routine thick and thin smears of these patients showed no parasite. It seems that the standard karyotype preparation technique with colchicine concentrates the microfilariae in samples where parasite load is small and not demonstrable with standard techniques. Serological tests are available for W. bancrofti and costly, whereas no regular serodiagnosis is available for B. malayi. In a country like India, both parasites are endemic and patients are treated on clinical suspicion when parasitaemia could be low. Low parasitaemia is common because of repeated infection and partial immunity. In such circumstances, a cost-effective concentration technique like this may be useful.