title: The onset time of amiodarone-induced thyrotoxicosis (AIT) depends on AIT type.
abstract: OBJECTIVE
  Considering the different pathogenic mechanisms of the two main forms of amiodarone-induced thyrotoxicosis (AIT), we ascertained whether this results in a different onset time as well.
  
  
  METHODS
  We retrospectively analyzed the clinical records of 200 consecutive AIT patients (157 men and 43 women; mean age 62.2±12.6 years) referred to our Department from 1987 to 2012. The onset time of AIT was defined as the time elapsed from the beginning of amiodarone therapy and the first diagnosis of thyrotoxicosis, expressed in months. Factors associated with the onset time of AIT were evaluated by univariate and multivariate analyses.
  
  
  RESULTS
  The median onset time of thyrotoxicosis was 3.5 months (95% CI 2-6 months) in patients with type 1 AIT (AIT1) and 30 months (95% CI 27-32 months, P<0.001) in those with type 2 AIT (AIT2). Of the total number of patients, 5% with AIT1 and 23% with AIT2 (P=0.007) developed thyrotoxicosis after amiodarone withdrawal. Factors affecting the onset time of thyrotoxicosis were the type of AIT and thyroid volume (TV).
  
  
  CONCLUSIONS
  The different pathogenic mechanisms of the two forms of AIT account for different onset times of thyrotoxicosis in the two groups. Patients with preexisting thyroid abnormalities (candidate to develop AIT1) may require a stricter follow-up during amiodarone therapy than those usually recommended. In AIT1, the onset of thyrotoxicosis after amiodarone withdrawal is rare, while AIT2 patients may require periodic tests for thyroid function longer after withdrawing amiodarone.
authors.affiliation: Endocrinology UnitDepartment of Clinical and Experimental Medicine, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, ItalyEndocrine UnitDepartment of Clinical and Experimental Medicine, University of Insubria, 21100 Varese, ItalyUnit of Epidemiology and BiostatisticsInstitute of Clinical Physiology, National Research Council, 56184 Pisa, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Tomisti
authors.affiliation: Endocrinology UnitDepartment of Clinical and Experimental Medicine, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, ItalyEndocrine UnitDepartment of Clinical and Experimental Medicine, University of Insubria, 21100 Varese, ItalyUnit of Epidemiology and BiostatisticsInstitute of Clinical Physiology, National Research Council, 56184 Pisa, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rossi
authors.affiliation: Endocrinology UnitDepartment of Clinical and Experimental Medicine, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, ItalyEndocrine UnitDepartment of Clinical and Experimental Medicine, University of Insubria, 21100 Varese, ItalyUnit of Epidemiology and BiostatisticsInstitute of Clinical Physiology, National Research Council, 56184 Pisa, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Bartalena
authors.affiliation: Endocrinology UnitDepartment of Clinical and Experimental Medicine, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, ItalyEndocrine UnitDepartment of Clinical and Experimental Medicine, University of Insubria, 21100 Varese, ItalyUnit of Epidemiology and BiostatisticsInstitute of Clinical Physiology, National Research Council, 56184 Pisa, Italy.
authors.forename: Enio
authors.initials: E
authors.lastname: Martino
authors.affiliation: Endocrinology UnitDepartment of Clinical and Experimental Medicine, University of Pisa, Ospedale Cisanello, Via Paradisa, 2, 56124 Pisa, ItalyEndocrine UnitDepartment of Clinical and Experimental Medicine, University of Insubria, 21100 Varese, ItalyUnit of Epidemiology and BiostatisticsInstitute of Clinical Physiology, National Research Council, 56184 Pisa, Italy fausto.bogazzi@med.unipi.it fbogazzi@hotmail.com.
authors.forename: Fausto
authors.initials: F
authors.lastname: Bogazzi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000638:Amiodarone / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013971:Thyrotoxicosis / Q000139:chemically induced* / Q000145:classification* / Q000000981:diagnostic imaging; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D000638:Amiodarone