In Sapporo, Japan, a neonatal screening program for congenital hypothyroidism (CH) has employed measurement of free thyroxine (T4) and TSH in the same filter-paper blood spot. This system has enabled us to identify primary CH and central CH during the neonatal period. The aim of this study was to clarify the prevalence and clinical characteristics of central CH. For this purpose, the screening program requested serum from infants with free T4 concentrations below the cut off value regardless of the TSH levels. Between January 2000 and December 2004, 83,232 newborns were screened and six central CH patients were detected as a result of follow-up of low free T4 and non-elevated TSH screening (1:13,872). This frequency is higher than in other studies. Four patients showed multiple pituitary hormone deficiency with pituitary malformations on magnetic resonance imaging. One patient was diagnosed as having Prader-Willie syndrome. The remaining patient was considered to have isolated central CH. Our study demonstrated that the frequency of central CH is 1:13,872. Free T4 measurement would also be advantageous in early recognition of multiple pituitary hormone deficiency.
Keywords: central CH; congenital hypothyroidism (CH); filter paper; free T4; neonatal mass screening.