Background

Although classic form of Hashimoto’s thyroiditis often presents as primary hypothyroidism, it can present as transient thyrotoxicosis (also known as Hashitoxicosis) at time of initial diagnosis. Hashimoto’s thyroiditis is considered as the most common autoimmune thyroid disease and remains a complex and ever-expanding disease of unclear pathogenesis with multiple variant forms.

Case Presentation

A 29-year-old man initially presented with hand tremors, increasing anxiety and frequent bowel motions and diagnosed with primary hyperthyroidism (TSH < 0.01 mIU/ml, free T4 19.7 pmol/L and free T3 6.4 pmol/L). He has strong family history of autoimmune diseases (Hashimoto’s thyroiditis in multiple cousins and aunt, type 1 diabetes in mother). Further investigations revealed strongly positive antithyroid peroxidase antibodies (396.8 IU/ml) and thyroglobulin antibodies (126.3 IU/ml) and negative thyroid stimulating immunoglobulin (< 0.1 IU/ml). Thyroid pertechnetate scan showed larger right thyroid lobe with more intense uptake (6.9 % with normal range 1.1-4 %). Thyroid gland was mildly enlarged but there were no discrete thyroid nodules identified on thyroid ultrasound. Right thyroid lobe showed reduced vascularity on ultrasound. He was diagnosed with Hashitoxicosis with unilateral thyroid lobe involvement and treated with carbimazole. Serial thyroid function tests showed subclinical hyperthyroidism (TSH < 0.01 mIU/ml with normal free T4) for over 15 months since commencement of antithyroid medications before achieving euthyroid state. Repeat thyroid autoantibodies showed persistent strongly positive antithyroid peroxidase antibodies (366 IU/ml) and thyroglobulin antibodies (96.8 IU/ml) and negative TSH receptor antibodies (< 0.3 IU/ml). Repeat thyroid ultrasound did not show any discrete thyroid nodules. 

Conclusion

This case highlights the unusual presentation of long standing Hashitoxicosis with interesting radiological findings of unilateral thyroid lobe involvement on ultrasound and thyroid uptake scan.