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Comparison between Thyroid Function Test and Radiographic Size of Knee Epiphysis in Neonates with Congenital Hypothyroidism

Journal of the Korean Pediatric Society 1999;42(8):1130-1135.
Published online August 15, 1999.
Comparison between Thyroid Function Test and Radiographic Size of Knee Epiphysis in Neonates with Congenital Hypothyroidism
An Sung Koh, Jae Ock Park, Dong Hwan Lee
Department of Pediatrics, College of Medicine, Soonchunhyang University, Seoul, Korea
선천성 갑상선 기능 저하증 신생아에서 갑상선 기능검사와 슬관절 화골핵 크기와의 관계
고안성, 박재옥, 이동환
순천향대학교 의과대학 소아과학교실
Correspondence: 
An Sung Koh, Email: 1
Abstract
Purpose
: Biochemical confirmation of congenital hypothyroidism takes about 10 days, which may result in a delay in diagnosis. The delay could be reduced if a faster method of investigation such as knee radiograph is used. The aim of this study is to assess the value of plain radiography of the knee in providing supportive evidence for the diagnosis of congenital hypothyroidism.
Methods
: Neonates with a screening TSH over 20μU/mL or free T4 under 0.85ng/dL were referred for further investigation during period of 1992-1998. We included 116 patients whose results were all available. Diagnosis was confirmed by measuring serum TSH, T4, free T4 by radioimmunoassay, radioisotope scan and ultrasonography of the thyroid. Radiography of the knee was obtained and ossification center sizes were measured.
Results
: Among 116 neonates, 31 were normal and congenital hypothyroisism was confirmed in 85 neonates. There was a statistically significant difference between the controls and the patients in regards to both biochemical data and knee epiphyseal ossification center size. In the congenital hypothyroidism group, there were a significant difference in biochemical data and knee epiphyseal ossification center size according to the diagnosis, and significant correlation between biochemical data and knee ossification center size, especially with serum T4 and combined mean epiphyseal diameter(r=0.56, P<0.01). In the patient group, simple regression equation was made between biochemical data and knee ossification center size. Combined mean epiphyseal diameter(mm) was 0.544 T4+4.161, combined epiphyseal surface area(mm2) was 2.940 T4+14.283. If T4 is below 7 μg/dL, combined mean epiphyseal diameter is below 8mm and surface area is below 34mm2.
Conclusion
: In neonates with abnormal thyroid screening, knee radiograph showing a combined mean epiphyseal diameter of 8mm or less and surface area of 34mm2 or less suggests congenital hypothyroidism prior to biochemical confirmation, requiring thyroxine treatment.
Key Words: Congenital hypothyroidism, Ossification center size of knee epiphysis


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