Etiological evaluation of primary congenital hypothyroidism cases

Primary congenital hypothyroidism is frequently seen endocrine disorder and one of the preventable cause of mental retardation. Aim of study was to evaluate the frequency of permanent/transient hypothyrodism, and to detect underlying reason to identfy any marker which carries potential to discriminate permanent/transient form.

Forty eight cases older than 3 years of age, diagnosed as primary congenital hypothyroidism and started thyroxin therapy in newborn-period, and followed up between January 2007-June 2013 were included in the study. Thyroid hormon levels were evaluated and thyroid ultrasonography was performed in cases who are at the end of their 3 years of age, after 6 weeks of thyroxine free period. Thyroid sintigraphy was performed if serum thyroid-stimulating hormone was high (≥ 5 mIU/mL) and perchlorate discharge test was performed if uptake was normal or increased on sintigraphy. Cases with thyroid-stimulating hormone levels ≥ 5 mIU/mL were defined as permanent primary congenital hypothyroidism group and as transient primary congenital hypothyroidism group with normal thyroid hormones during 6 months.

The mean age was 3.8±0.7 years. Mean diagnosis age was 16.6±6.5 days and 14 cases (29.2%) were diagnosed by screening program of Ministry of Health. There were 23 cases (14F, 9M) in permanent primary congenital hypothyroidism group and 12 (52.2%) of them were dysgenesis (8 hypoplasia, 4 ectopia), and 11 (47.8%) dyshormonogenesis. In transient primary congenital hypothyroidism group, there were 25 cases (17M, 8F). The mean thyroid-stimulating hormone levels at diagnosis were similar in two groups. The mean thyroxin dose in permanent primary congenital hypothyroidism group was significantly higher than transient group at the time of thyroxin cessation (2.1±0.7, 1.5±0.5 mg/kg/d, respectively, p=0.004). Thyroxin dose ≥1.6 mcg/kg/d was 72% sensitive and 69.6% specific for predicting permenant primary congenital hypothyroidism.

Transient primary congenital hypothyroidism is more frequent than expected and found often in males in the primary congenital hypothyroidism cases, started thyroxin therapy in neonatal period. While fT4, thyroid-stimulating hormone, Tg levels at diagnosis do not predict transient/permenant primary congenital hypothyroidism, thyroxin dose before the therapy cessation at the age of 3 may make the distinction between transient/permenant primary congenital hypothyroidism.