Fine-needle aspiration biopsy of the thyroid in an area of endemic goitre: influence of restored sufficient iodine supplementation on the clinical significance of cytological results

Objective: The iodine status of the population of Poland has markedly improved over the past years. The aims of this paper were: (i) to examine the diagnostic value of fine-needle aspiration biopsy (FNAB) of the thyroid in goitre endemic regions (in conditions of improved iodine supply), and (ii) to find whether the changes in iodine supply have already influenced the clinical interpretation of cytological results. Methods: Cytological diagnoses, based on 3782 aspirates, obtained from 3572 patients during the years 1985-1999, were verified by reference to the results of postoperative examinations. The relative occurrences of selected cytological results in 1992-1999 were also compared (patients not subjected to surgery were included). Results: We have found that the frequency of neoplastic lesions significantly decreased throughout the examined period (P < 0.02). The ratio of the papillary carcinoma frequency to the follicular carcinoma frequency increased from 1.7 during 1992-1993 up to 8.0 during 1998-1999 (P < 0.05). The frequency of cytologically diagnosed chronic thyroiditis increased from 1.5% in 1992 to 5.7% in 1999 (P < 0.001); the percentage of cytological diagnosis of 'follicular neoplasm' decreased during the same time (P < 0.001). The risk of malignancy significantly lowered in the cytological diagnoses of 'follicular neoplasm' from 15% during 1985-1993 to 6% during 1996-1999 (P < 0.05). Conclusions: The diagnostic value of FNAB during the period without proper iodine prophylaxis did not differ significantly from that during the last examined period. However, the changes in iodine supply have markedly and promptly affected the clinical significance of particular cytological results.