TRANSIENT CONGENITAL HYPOTHYROIDISM

CUT OFF VALUE FOR DIAGNOSIS AND TIME TO NORMALIZATION OF THYROID FUNCTION

Abstract

INTRODUCTION
Congenital hypothyroidism is one of the most commonly known cause of preventable mental retardation but detection at birth is difficult. As a continuum of this, screening programme was developed worldwide, which identified not only permanent hypothyroidism, but also group of disorders which was unidentified before due to unapparent clinical course namely transient congenital hypothyroidism (elevated thyroid stimulating hormone (TSH), decreased free thyroxine (FT4)) and transient congenital hyperthyrotropinaemia (elevated TSH, normal FT4). This study intended to look into cut off value for earlier discrimination between transient and permanent hypothyroidism, to determine median time for thyroid function to normalize upon cessation of treatment in transient group and its affecting factors.

METHODOLOGY
55 cases of congenital hypothyroidism were identified from retrospective record reviews. 37 cases were with permanent hypothyroidism and 18 cases were with transient hypothyroidism. The optimal cut off value of initial TSH and FT4 level were analyzed using receiver operating characteristics (ROC) curve analysis for both groups. Kaplan-Meier survival analysis was conducted to estimate median time for thyroid function to normalize within the transient hypothyroidism group. Both Simple and Multiple Cox Regression analysis were used to determine factors affecting the median time.

RESULTS
The cut off value for initial free T4 was 13.45 pmol/L with area under ROC curve of 70.5% (sensitivity 72.2%, specificity 64.7%). The median time obtained was 12 weeks and both the initial TSH and initial free T4 (p value <0.05) were the significant affecting factors identified.

CONCLUSION
The initial free T4 has a predictive value to differentiate between transient and permanent hypothyroid. It takes 12 weeks for thyroid function to normalize once treatment ceased and both initial TSH and initial free T4 affects the median time.