Multimodal distribution versus logarithmic transformation of thyroid volumes in adolescents: detection of subgroup with subclinical thyroid disorders and its impact on the assessment of the upper limit of normal thyroid volumes.
ENDOCRINE JOURNAL(2003)
摘要
Our objective was to evaluate whether there is a multimodal distribution of thyroid volume (ThV) in iodine-replete adolescents and to examine the relation between excessive ThV and the presence of thyroid hypoechogenicity (HE), serum thyroperoxidase antibodies (anti-TPO) and TSH levels >4.5 mU/l. ThV was measured by ultrasound in adolescents aged 13 yr (N = 1083) and 17 yr (N = 1089) from 22 schools in 6 districts of eastern Slovakia and expressed as ml and ml/m(2) body surface area. For each age group the multimodal distribution of ThV values was tested by computing their frequency at intervals of 0.5 ml/m(2) and plotting the cumulative frequency on a probability scale in which each segment with normal distribution should give a straight line. In all examined subjects the HE was evaluated by ultrasound; in 924 (42.5%) of those anti-TPO was estimated by radioimmunoassay and TSH by immuno-electrochemiluminiscent assay. The medians of urinary iodine found in 55-164 spot urine samples from each of 6 districts (total number = 1003) were 126-142 mug/l, indicating an iodine-replete status. There was a trimodal distribution of ThV in each group, 80-85% in the lowest, 10-15% in the middle, and 5-7% in the upper segments. In the 10th ThV decile of the 17-yr group the frequency of HE (33/109 = 30.3%), anti-TPO (13/62 = 21.0%) and TSH (6/62 = 9.7%) was significantly higher than that in the 1st-9th decile (71/980 = 7.2%, P < 0.001; 23/482 = 4.8%, P < 0.001 and 5/482 = 1.0%, P < 0.001, resp.). Similar differences were found in the 13-yr group (21/109 = 19.2% vs. 58/974 = 5.9%, P < 0.001 for HE, 5/60 = 8.3% vs. 3/320 = 0.9%, P < 0.001 for anti-TPO and 2/64 = 3.1% vs. 4/317 = 1.3% (not significant) for TSH >4.5 mU/l. Thus in the 10% of subjects with the highest ThV, the frequency of HE and anti-TPO was 4-5 times higher than in the remaining 90%. Our data indicate that an epidemiological evaluation of a large population of adolescents can detect a group with early signs of thyroid dysfunction (e.g. excessive ThV, increased frequency of HE, anti-TPO and TSH >4.5% mU/l), although such dysfunction may not be clinically apparent. This contrasts with numerous earlier reports which used a logarithmic transformation of the data in similar ThV sets, thus making the data appear homogeneous (unimodal) and with a normal distribution and obscuring the true multimodal distribution. This further prevents recognition of subjects with evidence of disordered thyroid status which thus become falsely included into a normal range.
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关键词
adolescents,ultrasound,normal thyroid volume,multimodal distribution,genetic factors
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