Endocrine Abstracts

Introduction: Subacute thyroiditis (SAT) is an acute inflammatory disorder which can rarely present as pyrexia of unknown origin without other symptoms. Diffuse thyroid heterogeneity, focal hypoechoic areas and decreased/normal gland vascularity are the most common ultrasound findings of SAT. We report a case of asymptomatic SAT presenting as bilateral thyroid nodules and pyrexia of unknown origin.

Case Presentation: A 72-year-old male with a history of tachycardia/bradycardia syndrome (with pacemaker implantation) and thyroid nodule of the left lobe (Bethesda II) was referred to emergency department due to a 2-week history of fever. He complained of a 5 kg weight loss in last 3 months, with no other symptoms. Clinical examination was unremarkable, apart from patient being febrile. Blood tests revealed anemia, leukocytosis, increased inflammation markers and thyrotoxicosis (TSH 0.01 μIU/l, fT4 31.13 pmol/l, NR: 9-19) with negative anti-TPO, anti-TG and TRAb antibodies. Further investigations were negative for infections and autoimmune diseases, while bone marrow aspiration biopsy was normal. Whole body CT scan showed hypoechogenic lesions in both thyroid lobes but no other findings. Due to exposure to intravenous iodine contrast, thyroid scintigraphy was not performed. Thyroid ultrasound revealed a 4.4×2.3 cm well marginated isoechoic nodule in the right lobe with regular shape, cystic degeneration and hypoechoic halo sign with peripheral/central vascularity (EU-TIRADS 3) and two other nodules in the left lobe, 3.6×2.5 cm and 1.2×2.2 cm, (EU-TIRADS 3) with similar features to the right lobe nodule. Cytology of the two larger nodules revealed atypia of undetermined significance (Bethesda III). Treatment with naproxen 500 mg twice daily for the pyrexia and thiamazole 10 mg daily for the thyrotoxicosis was initiated. One-week later, patient was afebrile, improved thyroid function and decreased inflammation markers were noted; naproxen was continued, while thiamazole was stopped due to borderline fT4 levels. After one month of treatment, naproxen was finally discontinued due to normal inflammation markers and thyroid function. The patient was reviewed three months later and remained asymptomatic and euthyroid without treatment. Repeat thyroid ultrasound revealed complete remission of the 4.4 cm and 3.6 cm nodules and presence of the, already known, 1.5 cm nodule in the left lobe.

Conclusion: This very rare case demonstrates the importance of SAT to be included in the differential diagnosis of fever of unknown origin, even in asymptomatic patients. Furthermore, clinicians should be aware that, in some cases, SAT-associated thyroid lesions may mimic thyroid nodules.