Antithyroid Peroxidase Antibodies in Multinodular Hashimoto's Thyroiditis Indicate a Variant Etiology

Hashimoto's thyroiditis (HT) is a common autoimmune thyroid disorder, which predominantly presents as a diffuse goiter, with few studies which report HT presenting as multinodular goiter, with variable frequencies ranging from 59% to 78.6% especially from south Indian populations. This variant clinical presentation may have diagnostic challenges which require further analysis. Anti-TPO antibodies are more common (90-95%) in Hashimoto's thyroiditis than anti-TG antibodies in Hashimoto's thyroiditis. This study analyzes the clinical features and the correlation of anti-TPO levels with diffuse and multinodular forms of HT.

This study was conducted in the Department of General Surgery in a tertiary care hospital in south Tamil Nadu. Patients presenting with clinical features of a thyroid disorder were interviewed and given a detailed clinical, radiological examination and guided FNAC. Those patients diagnosed by FNAC as HT were registered and a sample of 3cc of blood was drawn for T3, T4, TSH, and anti-TPO analysis. All the data were tabulated.

Of the 212 patients who presented with goiters, 96 were diagnosed by FNAC as having a cytological picture suggestive of Hashimoto's thyroiditis. Of these 96 patients with HT, 46 (47.9%) were multinodular (HT-MNG), 14 (14.58%) were solitary nodules (HT-SNT), and the remaining 36 (37.5%) were diffuse goiters (HT-D). Of the 46 patients who are HT-MNG, 36.9% had elevated anti-TPO-Ab (more than 35.0U/l) and 63.1% had normal/lower values (less than 35.0U/l). But of 36 patients with HT-D, 77.7% had elevated anti-TPO-Ab levels (>35U/l). Chi square statistics was 15.8346 and the p value is 0.0005 (<.05). Eight cases of HT-D and 3 cases of HT-MNG had hyperthyroidism and 3 cases of HT-D had hypothyroidism and all other cases were in euthyroid state.

Patients presenting as multinodular Hashimoto's thyroiditis have low prevalence of elevated anti-TPO-Ab than diffuse HT which suggests that multinodular form of Hashimoto's thyroiditis is a unique clinical entity with etiopathogenesis that is at variance with the diffuse form.