SAT-426 Macro-Thyroid Stimulating Hormone (TSH) in Children

Abstract

Macro-TSH is mainly a complex of TSH with anti-TSH autoantibodies. Due to its large molecular size (>150 kDa), it accumulates in the circulation resulting in elevated serum TSH concentrations. Because the bioactivity of macro-TSH is low, treatment with thyroxine is not necessary. The prevalence of macro-TSH is no more than 1% in adult patients with subclinical hypothyroidism. However, the prevalence of macro-TSH in children is not known. We report here two cases of macro-TSH in pediatric setting.[Case reports] Case 1. Six-year and eight-month-Japanese boy visited a pediatric hospital because of hyperactivity disorder. Physical examination revealed that he had a slight mental retardation (IQ 63 by Tanaka-Binet test). Thyroid tests showed that fT4 1.21 ng/dL, TSH 120.4 µU/mL, Tg antibody 1.9 IU/mL, TPO antibody <0.1 IU/mL. His serum was sent to our laboratory to examine the causes of inappropriate high serum TSH concentration. Case 2. Eight-year and three-month-Turkish girl was brought to a pediatric hospital by her parents because of her yellowish palms, which was not identified at the hospital. She did not have any complaints and physical signs attributable to thyroid dysfunction. Laboratory data disclosed that fT4 1.5 ng/dL, TSH 19.6 µU/mL, Tg Ab negative, TPO Ab negative. Levothyroxine treatment started but serum TSH concentration was still high (39.0 µU/mL) after two months. Her serum sample was sent to our laboratory to examine the causes of inappropriate high serum TSH concentrations.[Lab. Tests for macro-TSH]When serum was mixed with the same amount of 25% polyethylene glycol (PEG) and γ-globulin fraction was precipitated, TSH concentration in the supernatant decreased significantly from 109.3 µU/mL to 2.3 µU/mL (PEG precipitation ratio 97.9%) in case 1, and from 17.3 µU/mL to 0.15 µU/mL (PEG precipitation ratio 99.1%) in case 2. HAMA blockers did not significantly change TSH concentration in both cases. High proportion of serum TSH bound to a protein G column, which binds IgG, in case 1 (91.3%) and in case 2 (57.7%), indicating that TSH was associated with IgG. Gel filtration chromatography (GFC) revealed that TSH was mostly eluted at the fraction > 150 kDa rather than 28 kDa of authentic TSH in both cases. Serum was incubated with 37.7 µU of TSH for one hour and subjected to GFC. TSH concentration in the fraction of 150 kDa (macro-TSH) increased from 2.8 µU/mL to 5.6 µU/mL in case 1 and from 0.4 µU/mL to 2.0 µU/mL in case 2, suggesting that macro-TSH was produced by the binding of exogenous TSH to anti-TSH autoantibodies.[Conclusion]Macro-TSH exists in children and careful evaluation is required in patients with inappropriate high serum TSH concentrations to avoid unnecessary treatment.