title: Serum negative autoimmune thyroiditis displays a milder clinical picture compared with classic Hashimoto's thyroiditis.
abstract: BACKGROUND
  Despite high sensitivity of current assays for autoantibodies to thyroperoxidase (TPO) and to thyroglobulin (Tg), some hypothyroid patients still present with negative tests for circulating anti-thyroid Abs. These patients usually referred to as having seronegative autoimmune thyroiditis (seronegative CAT) have not been characterized, and definite proof that their clinical phenotype is similar to that of patients with classic chronic autoimmune thyroiditis (CAT) is lacking.
  
  
  OBJECTIVE
  To compare the clinical phenotype of seronegative CAT (SN-CAT) and CAT as diagnosed according to a raised serum level of TSH with negative and positive tests for anti-thyroid Abs respectively.
  
  
  METHODS
  A case-control retrospective study enrolling 55 patients with SN-CAT and 110 patients with CAT was performed. Serum free triiodothyronine (FT3), free thyroxine (FT4), TSH, Tg Abs, and TPO Abs were measured in all patients.
  
  
  RESULTS
  Patients with SN-CAT displayed significantly lower mean levels of TSH (6.6±3.4 vs 10.2±9.8 μU/ml; P=0.009), higher mean FT4 levels (1.1±0.2 vs 0.9±0.2 ng/dl; P=0.0002), and similar FT3 levels when compared with CAT patients. Mean thyroid volume was significantly greater in patients with CAT when compared with SN-CAT patients (11.2±6.5 vs 8.1±3.7 ml; P=0.001). Logistic regression demonstrated that FT4 (0.123 (0.019-0.775); (P=0.026)) and thyroid volume (1.243 (1.108-1.394); (P=0.0002)) were significantly and independently related to the diagnosis (CAT/SN-CAT). Patients with SN-CAT had a similar prevalence of thyroid nodules and female gender but a lower prevalence of overt hypothyroidism (5.4 vs 20.9%; P=0.012) as opposed to patients with CAT.
  
  
  CONCLUSIONS
  These results suggest an autoimmune etiology of SN-CAT, which, however, seems to have a milder clinical course when compared with CAT.
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Rotondi
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: de Martinis
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Coperchini
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Pignatti
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Pirali
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Ghilotti
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Fonte
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy.
authors.forename: Flavia
authors.initials: F
authors.lastname: Magri
authors.affiliation: Unit of Internal Medicine and EndocrinologyFondazione Salvatore Maugeri I.R.C.C.S., Laboratory for Endocrine Disruptors, Chair of EndocrinologyAllergy and Immunology UnitFondazione Salvatore Maugeri I.R.C.C.S., University of Pavia, Via S. Maugeri 10, I-27100, Pavia, Italy lchiovato@fsm.it.
authors.forename: Luca
authors.initials: L
authors.lastname: Chiovato
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood; D016022:Case-Control Studies; D005260:Female; D050031:Hashimoto Disease / Q000097:blood* / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D009195:Peroxidase / Q000378:metabolism; D013954:Thyroglobulin / Q000378:metabolism; D013967:Thyroiditis, Autoimmune / Q000097:blood* / Q000378:metabolism; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D013954:Thyroglobulin; D009195:Peroxidase