Riedel's Thyroiditis with Intense FDG Uptake Demonstrated on FDG PET/CT

A 39 year old female presented with rapidly enlarging goitre, minimal obstructive symptoms and no constitutional symptoms. Clinical examination revealed diffusely enlarged, firm, non-tender thyroid gland. Biochemical investigations showed subclinical hypothyroidism, positive thyroid antibodies and unremarkable inflammatory markers. Ultrasound examination and CT scan of the neck were suspicious of Riedels thyroiditis. The patient was referred for a FDG PET scan to evaluate for systemic fibro-inflammatory process or lymphoma. Subsequent core biopsy of the thyroid gland demonstrated a chronic inflammatory process with fibrosis consistent with Riedels thyroiditis. A FDG PET/CT study showed diffuse FDG uptake in the thyroid gland and no abnormal retroperitoneal FDG uptake elsewhere to suggest active retroperitoneal fibrosis. The goitre reduced in size with thyroid hormone replacement and steroids, however the patient was lost to follow up.