Primer Konjenital Hipotiroidili Hastalarda, Na-L Tiroksin Tedavisinin Serum Tiroid Hormon Düzeylerine Etkisinin Incelenmesi

Abstract

Congenital hypothyroidism (CH) is the most common endocrinologic problem in the neonatal period with an incidence of 1:3000-1:4000. In clinical guidelines, it is recommended that high-dose Na-L thyroxine (10-15 mcg/kg/day) be started in order to bring serum thyroid hormone levels to normals promptly. On the other hand, it has been stated that high-dose Na-L thyroxine therapy could cause iatrogenic hyperthyroidism. In societies with iodine deficiency, one of the most common causes of primary CH is transient CH. In our country, transient CH is seen commonly due to widespread iodine deficiency. In these patients, unlike patients with permanent primary CH, serum hormone levels can be normalised with lower doses of thyroid homrone therapy. In this study, the objective was to investigate the effect of Na-L thyroxine therapy on serum thyroid hormone levels in patients with primary CH. Patients were classifed according to underlying etiology and disease severity; and the time it took for different initial Na-L thyroxine doses to bring serum thyroid hormone levels to target levels was evaluated. 71 patients diagnosed with CH in the Pediatric Endocrinology Unit in 2004-2009 were included in the study. 33 patients (46.4%) had permanent and 31 (43.7%) had transient CH. Seven patients (9.9%) had subclinical hypothyroidism of unknown cause. Serum fT4 levels reached the upper half of normal range (> 17 pmol/L) in 16, 16 and 19 days in infants with permanent CH, transient CH and subclinical hypothyroidism, respectively. Serum TSH levels declined below 10 mIU/L in a median of 19, 16 and 19 days in infants with permanent CH, transient CH and subclinical hypothyroidism, respectively. There was no significant difference among the three groups of diagnoses in terms of the duration of achieving treatment goals. The patients were classifed into three groups according to disease severity using serum fT4 levels at the time of diagnosis as mild (8,1-12 pmol/L), moderate (4,1-8 pmol/L) and severe (<4 pmol/L). Initial mean Na-L thyroxine doses for mild, moderate and severe disease groups were 6.22±3.17, 9.94±2.32 and 10.45±2.37 mcg/kg/day, respectively. Serum fT4 levels were measured in the upper half of normal range (>17 pmol/L) in a median of 18, 14 and 16 days in patients with mild, moderate and severe CH, respectively. Serum TSH levels were measured below 10 mIU/L in a median of 18,16 and 30 days in patients with mild, moderate and severe CH, respectively. There was no significant difference among the three groups of disease severity in terms of the duration of achieving treatment goals. The patients were also classified into two as those receiving initial low-dose and high-dose therapy, according to Na-L thyroxine doses. Serum fT4 levels reached the upper half of normal (>17 pmol/L) in a median of 14 days in patient initiated with high-dose, and in a median of 18 days with low-dose therapy. The median duration it took for TSH to decline below 10 mIU/L was 18 days both in high-dose and low-dose therapy groups. There was no significant difference between patients on high-dose and low-dose therapy in terms of the duration of achieving treamtnet goals. As a result, it was observed as opposed to clinical guidelines that not all patients diagnosed with CH required high-dose Na-L thyroxine. In this study, it is recommended that patients with mild, moderate and severe CH initially receive 6-8 mcg/kg/day, 8-10 mcg/kg/day and 10 mcg/kg/day or higher doses of Na-Lthyroxine, respectively.