title: Risk for progression to overt hypothyroidism in an elderly Japanese population with subclinical hypothyroidism.
abstract: BACKGROUND
  Few population-based studies report the changes with time in thyroid function tests in patients with subclinical hypothyroidism. We compared the risk for developing overt hypothyroidism in patients with subclinical hypothyroidism and euthyroid controls from the same population of elderly Japanese. We also sought associations of selected parameters with the development of overt hypothyroidism in the subclinical hypothyroid and euthyroid groups.
  
  
  METHODS
  We measured thyrotropin (TSH) and free thyroxine (T4) levels at baseline examinations performed from 2000 to 2003 in the cohort of Japanese atomic-bomb survivors and identified 71 patients with spontaneous subclinical hypothyroidism (normal free T4 and TSH >4.5 mIU/L without a history of thyroid treatment, mean age 70 year) and 562 euthyroid controls. We re-examined TSH and free T4 levels an average of 4.2 years later (range, 1.9-6.9).
  
  
  RESULTS
  The risk for progression to overt hypothyroidism was significantly increased in subclinical hypothyroid patients (7.0%) compared with control subjects (1.6%) after adjusting for age and sex (odds ratio, 4.56; p=0.009). Higher baseline TSH levels were associated with progression from subclinical to overt hypothyroidism (p=0.02) in the multivariate analysis, including age, sex, antithyroid peroxidase antibody, and ultrasonography (US) findings. The analysis using binary TSH data suggested that a TSH level >8 mIU/L was a predictive value for development of overt hypothyroidism (p=0.005). On the other hand, serum TSH levels spontaneously normalized in 38 (53.5%) of the patients with subclinical hypothyroidism. In the multivariate analysis, normalization of TSH levels was associated with lower baseline TSH levels (p=0.004) and normal and homogenous thyroid US findings (p=0.04). Atomic-bomb radiation dose was not associated with subclinical hypothyroidism or its course.
  
  
  CONCLUSIONS
  Subclinical hypothyroidism was four times more likely to be associated with development of overt hypothyroidism than euthyroid controls in the sample population of Japanese elderly. TSH levels in half of the patients normalized spontaneously when assessed after an average follow-up period of 4.2 years. Baseline TSH level and thyroid US findings are potential predictors of future thyroid function in subclinical hypothyroidism.
authors: Department of Clinical Studies, Radiation Effects Research Foundation, Hiroshima, Japan. misaima@rerf.or.jp
authors: Misa
authors: M
authors: Imaizumi
authors: Nobuko
authors: N
authors: Sera
authors: Ikuko
authors: I
authors: Ueki
authors: Ichiro
authors: I
authors: Horie
authors: Takao
authors: T
authors: Ando
authors: Toshiro
authors: T
authors: Usa
authors: Shinichiro
authors: S
authors: Ichimaru
authors: Eiji
authors: E
authors: Nakashima
authors: Ayumi
authors: A
authors: Hida
authors: Midori
authors: M
authors: Soda
authors: Tan
authors: T
authors: Tominaga
authors: Kiyoto
authors: K
authors: Ashizawa
authors: Renju
authors: R
authors: Maeda
authors: Shigenobu
authors: S
authors: Nagataki
authors: Masazumi
authors: M
authors: Akahoshi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People / Q000706:statistics & numerical data; D001323:Autoantibodies / Q000097:blood; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000453:epidemiology*; D007453:Iodide Peroxidase / Q000276:immunology; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D054043:Nuclear Weapons; D015995:Prevalence; D012306:Risk; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000201:enzymology; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014463:Ultrasonography
chemical_list: D001323:Autoantibodies; D013972:Thyrotropin; D007453:Iodide Peroxidase; D013974:Thyroxine