Thyroid tuberculosis - role of PCR in diagnosis of a rare entity

Tuberculosis is a rare cause of granulomatous thyroiditis, whose diagnosis may be difficult with routine cytopathology and staining for acid-fast bacilli (AFB).

Amongst 7962 cases of various thyroid lesions subjected to fine needle aspiration cytology (FNAC) over a period of 12 years, 34 cases (0.43%) were found to have cytological features of granulomatous inflammation with or without necrosis, which could be due to tuberculosis, granulomatous thyroiditis or other causes of granulomatous inflammation such as sarcoidosis or fungal infections. DNA was extracted from the material available on May-Grünwald-Giemsa-stained smears from the archival material. PCR for Mycobacterium tuberculosis was performed for insertion sequence IS6110.

The age of the patients ranged from 32 to 58 years (median 48 years); 24 were female and 10 male. FNAC from thyroid swellings showed epithelioid granulomas with giant cells and/or necrosis. Although acid-fast bacilli were only seen in smears in two cases, 19/34 (55.9%) showed the presence of 123 bp DNA band under ultraviolet transillumination. Five control cases were negative.

Our study of archival cytological material illustrates the importance of PCR as a potentially useful tool for the detection of M. tuberculosis DNA from FNAC of thyroid lesions, which could provide an alternative for rapid diagnosis of thyroid tuberculosis in AFB-negative cases.