title: Comparison of Antithyroglobulin Antibody Concentrations Before and After Ablation with 131I as a Predictor of Structural Disease in Differentiated Thyroid Carcinoma Patients with Undetectable Basal Thyroglobulin and Negative Neck Ultrasonography.
abstract: BACKGROUND
  Patients with differentiated thyroid carcinoma are submitted to a first assessment several months after initial therapy to evaluate their response to treatment. At that assessment, measurement of basal thyroglobulin (Tg) and antithyroglobulin antibodies (TgAb) and neck ultrasonography (US) are recommended. Serum Tg may be falsely negative in the presence of TgAb, and the management of patients with negative Tg but positive TgAb represents a challenge. The objective of this study was to correlate the variation in TgAb concentrations (comparison before and after ablation with (131)I) with the risk of structural disease.
  
  
  METHODS
  The sample consisted of 116 low- or intermediate-risk patients who had undetectable Tg, negative US at initial assessment, and positive TgAb 8-12 months after thyroidectomy and ablation with (131)I.
  
  
  RESULTS
  Comparison of TgAb concentrations before and after ablation with (131)I showed a reduction of >50% in 56 patients (group A), a reduction of <50% in 35 patients (group B), and an increase in 25 patients (group C). Metastases were detected in 5/116 (4.3%) patients during initial assessment (lymph nodes in two, pulmonary in two, and bone in one). They were diagnosed in 0/56, 2/35 (5.7%), and 3/25 (12%) patients of groups A, B, and C, respectively. During follow-up, metastases were detected in 7/111 (6.3%) patients (lymph nodes in six, and pulmonary in one). They occurred in 1/56 (1.8%), 3/33 (9%), and 3/22 (13.6%) patients of groups A, B, and C, respectively. Thus, structural disease was found in 1.8%, 14.3%, and 24% of groups A, B, and C, respectively. This rate was 4% in low-risk patients and 15.4% in intermediate-risk patients.
  
  
  CONCLUSIONS
  Among patients with undetectable Tg, negative US, and positive TgAb after ablation with (131)I, the frequency of structural disease was <5% in patients, with >50% reduction in TgAb. Among patients without a significant reduction in TgAb, approximately 10% of low-risk patients and >20% of intermediate-risk patients had structural disease. These results help define the indication for imaging methods other than US during initial assessment and long-term follow-up.
authors.affiliation: 1 Postgraduation Program, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .|2 Endocrinology Service, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .
authors.forename: Pedro Weslley
authors.initials: PW
authors.lastname: Rosario
authors.affiliation: 1 Postgraduation Program, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .
authors.forename: Marina
authors.initials: M
authors.lastname: Carvalho
authors.affiliation: 1 Postgraduation Program, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .|2 Endocrinology Service, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .
authors.forename: Gabriela Franco
authors.initials: GF
authors.lastname: Mourão
authors.affiliation: 2 Endocrinology Service, Santa Casa de Belo Horizonte , Minas Gerais, Brazil .
authors.forename: Maria Regina
authors.initials: MR
authors.lastname: Calsolari
mesh_terms: D000328:Adult; D000368:Aged; D000906:Antibodies / Q000097:blood*; D001323:Autoantibodies / Q000097:blood*; D002277:Carcinoma / Q000097:blood* / Q000000981:diagnostic imaging / Q000276:immunology / Q000628:therapy; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000737:chemistry*; D008198:Lymph Nodes / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging / Q000473:pathology; D009362:Neoplasm Metastasis; D011446:Prospective Studies; D012306:Risk; D013954:Thyroglobulin / Q000097:blood; D013964:Thyroid Neoplasms / Q000097:blood* / Q000000981:diagnostic imaging / Q000276:immunology / Q000628:therapy; D013965:Thyroidectomy; D014463:Ultrasonography
chemical_list: D000906:Antibodies; D001323:Autoantibodies; D007457:Iodine Radioisotopes; C006606:anti-thyroglobulin; D013954:Thyroglobulin