Background: Hashimoto's thyroiditis (HT) is a chronic autoimmune thyroiditis typically resulting in hypothyroidism. In itself, HT is not an indication for surgery but the co-existence of thyroid nodular disease creates diagnostic and management difficulties. Indications for thyroidectomy include risk of malignancy and pressure symptoms. While fine needle aspirate cytology is effective in the diagnosis of thyroid lesions, in HT there is increased diagnostic uncertainty. This study aimed to document the results of cytology and the rate of malignancy in HT.
Methods: Data were analysed for the period 1996–2009. All patients who underwent thyroidectomy and had a formal histological diagnosis of HT were included and compared with a control population who underwent thyroidectomy but did not have HT. In both groups, patient demographics, clinical parameters, cytology findings, operative procedure and final histology were reviewed.
Results: One hundred and twelve patients had histologically proven HT, with a significant female preponderance compared with controls (P = 0.002). There were no significant differences between cases and controls for type of procedure or preoperative examination findings. Incidence of hypothyroidism was increased: 17 patients (15.2% versus 1.6%; P < 0.0001), whereas thyrotoxicosis was decreased: four patients (3.6% versus 14.4%; P = 0.002). There was an increased incidence of follicular/indeterminate cytology (35.7% versus 22.1%; P = 0.001). While there was an increased false negative rate in HT, this failed to achieve statistical significance (8.8% versus 2.5%; P = 0.09). Malignancy rates were more prevalent in the setting of HT (23.2% versus 11.4%; P < 0.001).
Conclusions: Given the increased rate of associated malignancy and increased diagnostic uncertainty in patients with HT, we recommend routine preoperative thyroid antibody measurement.