Thyroid function during long-term GH treatment in children affected by idiopathic GH deficiency

A. Ciresi; V. Guarnotta; C. Perrone; A. Galluzzo; C. Giordano

Alterations in the thyroid axis have been reported following GH therapy both in adults and children with GH deficiency (GHD), even if the clinical significance of these changes, in small and short-term studies, remains uncertain. To evaluate the impact of GH replacement on thyroid status in a large selected cohort of prepubertal children with idiopathic GHD during a 3-years follow-up. Study outcome considered FT3, FT4 and TSH modifications (delta) during therapy and their correlations with IGF-1, biochemical and auxological data. Data of 105 children (82 M, 23 F; mean age 11.13) were retrospectively analysed. At diagnosis, the areas under the curve of GH (AUCGH) were calculated during GHRH-Arg test and ITT. At baseline and yearly up to 36 months during GH treatment, we measured height-velocity, BMI, IGF-1, FT3, FT4, TSH. A significant FT3 delta (P<0.001) was documented in 89/105 (84.7%) patients at 12 months after starting GH treatment, without any further change at 24 and 36 months. No significant FT4 and TSH delta were observed during the follow-up. Grouping all patients according to FT3 delta at 12 months in those with lower (No 80, 76%) or greater value than 75 percentile (No 25, 24%), the latter showed significantly lower AUCGH during GHRH-Arg (P=0.018) and ITT (P=0.023). These children also showed lower FT3 levels at baseline (P<0.001), without difference in FT4 and TSH. No significant differences in auxological parameters were detected between the two groups. In GHD children, GH treatment is associated with a significant increase in FT3 levels in the first 12 months. However, the lack of significant effects of these changes in relation to the auxological parameters does not suggest the routinely monitoring of thyroid function in initially euthyroid patients.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.

**Table 1**
	baseline	12 months	24 months	36 months
Height (S.D.)	−2.11±0.89	−1.73±0.75	−1.44±0.76	−1.03±0.85
IGF-1 (μg/l)	98.83±47.94	314.68±193.25	330.30±172.95	349.90±145.88
FT3 (pg/ml)	3.10±0.94	4.13±0.53	4.12±0.53	4.21±0.53
FT4 (ng/dl)	1.25±0.24	1.25±0.28	1.19±0.25	1.19±0.23
TSH (μU/ml)	1.98±0.84	1.92±0.97	1.95±1.03	1.51±0.54
Δ FT3	–	1.02±1.08*	0.02±0.73	0.07±0.44
Δ FT4	–	0.01±0.04	0.06±0.01	0.01±0.02
Δ TSH	–	0.06±0.13	0.03±0.06	0.44±0.59
Δ IGF-1	–	217.6±181.5*	26.2±153.3*	44.3±98.5*
* P<0.005.

Endocrine Abstracts

P1004