The impact of iodine deficiency exposure on thyroid nodule cytology and pathology – A single institute, case-control study

Objective: The association between follicular carcinoma and iodine deficiency (ID) is based on epidemiological studies and their inherent biases. The aim of the study was to assess the impact of long-term ID exposure on thyroid nodule cytology and final pathology in a distinct group of patients within a single institution. Methods: Ethiopian origin patients were compared to an aged-matched group of non-Ethiopian patients. Demographics, risk factors, clinical presentation, cytology and pathology were collected and compared. Final outcomes were cytology and pathology distribution. Results: A total of 489 (246 Ethiopian, 243 control) nodules of 461 patients (230 and 231 respectively) were included. Ethiopian patients had lower rates of thyroid cancer risk factors (p=0.05). Cytology analysis demonstrated significant group differences (p=0.03), as Ethiopian patients had higher rates of benign cytology (85% vs. 75.7%, respectively). Pathology analysis demonstrated a significantly lower malignancy rate among Ethiopian patients (39.2% (20/51) vs. 63.3% (31/49), p=0.027, respectively). The Ethiopian group had a significant higher rate of follicular carcinoma compared to the control group (25% [5/20] vs. 3.2% [1/31], p=0.034, respectively) and lower rates of papillary thyroid carcinoma (25% [5/20] vs. 61.3% [19/31], p=0.017, respectively). Conclusions: The association between ID and FC exists years following immigration and exposure to a better iodine diet, implying that differentiation may be affected in earlier stages and levels of exposure.