ANISHING THYROID NODULES

SUBACUTE THYROIDITIS MIMICKING SUSPICIOUS THYROID NODULES IN A PATIENT ON TYROSINE KINASE INHIBITOR

Abstract

INTRODUCTION/BACKGROUND
Dasatinib is a tyrosine kinase inhibitor (TKI) used as a second-line treatment for chronic myeloid leukaemia. Thyroid dysfunction is rare with dasatinib. We report a patient with chronic myeloid leukaemia on Dasatinib who developed subacute thyroiditis mimicking a suspicious thyroid nodular disease.

CASE
A 57-year-old female was started on dasatinib in June 2021. She presented with a one-month history of fever, palpitations, heat intolerance, and neck swelling in April 2023. Her thyroid function tests (TFTs) showed elevated free-T4 30.9 pmol/ and suppressed thyroid stimulating hormone (TSH), <0.008 m IU/L, hence, carbimazole 20 mg daily was initiated. Thyroid ultrasound revealed hypoechoic solid nodules at both upper poles, measuring 1.7 x 2.1 x 4.7 cm and 1.7 x 2.0 x 3.4 cm, respectively. Both nodules had TIRADS scores of 5. Another hypoechoic solid nodule with a TIRADS score of 4 was also found at the right mid-pole. However, during the scheduled ultrasound-guided fine needle biopsy two months later, the repeat ultrasound no longer showed any thyroid nodule. TSH-receptor antibody was negative. Her thyroid function normalised and her carbimazole dose was tapered off after 2 months of treatment. Repeat neck ultrasound six months later demonstrated a normal thyroid gland. The subsequent serial TFTs remained normal. Dasatinib was continued throughout this period. TKI-induced thyroid abnormality usually appears within the first 6 months but can still manifest after the first year of treatment. Ultrasound descriptions of subacute thyroiditis include diffuse heterogeneity, focal hypoechogenicity, decreased vascularity, as well as nodular lesions which can be mistaken for malignancy.

CONCLUSION
TFT measurement prior to TKI initiation is recommended, with repeat tests every 6 weeks for the first 6 months, every 3–6 months for a year, then biennial screening beyond the first 18 months of therapy. Recognition of sonographic patterns of subacute thyroiditis is important to avoid unnecessary procedures or increased patient anxiety.