LAUSR

A 61-year-old woman presented with a 5-year history of progressive and painless neck swelling and hypothyroidism. Neck ultrasound revealed diffuse thyroid enlargement (up to 8.0 cm). Antibody titres against thyroglobulin and thyroperoxidase were elevated. Serum IgG4 was remarkably elevated (10,300 mg/L; reference, 80–1400 mg/L). Ultrasound-guided biopsy of the thyroid revealed infiltration of enriched lymphoplasmacytic cells and fibrosis. IgG4positive lymphoplasmacytic cells were over 50/high power field and the overall IgG4/IgG ratio was above 60%. These findings are consistent with IgG4-related disease (IgG4-RD) of the thyroid gland. Considering the known possibility of systematic manifestations associated with this disorder, the physicians recommended F-FDG PET/CT scanning to confirm or exclude the involvement of other organs. PET/ CT demonstrated thyroid enlargement with diffuse and intense FDG activity (a–d, arrows, SUVmax 10.1). There was no other abnormal FDG activity elsewhere to suggest IgG4RD involvement. Therefore, a diagnosis of isolated involvement of the thyroid gland with IgG4-RD was established. The patient received prednisone therapy, and the thyroid enlargement was reversed in a week. IgG4-RD is an autoimmune-mediated inflammatory disease characterised by multi-organ involvement, including the pancreas, liver, bile duct, salivary glands, kidney, lymph nodes, and retroperitoneum [1, 2]. To the best of our knowledge, this report is the first to describe the isolated involvement of thyroid gland by IgG4-RD using F-FDG PET/CT scanning. This case highlights a rare occurrence of isolated involvement of the thyroid gland by this entity, and the value of F-FDG PET/CT in evaluating organ involvement.