Transient Congenital Hypothyroidism in Turkey: An Analysis on Frequency and Natural Course

Abstract

Objective: Prevalence of congenital hypothyroidism (CH) in Turkey at birth was reported to be as high as 1:650 in 2008-2010. Incidence rates of permanent and transient CH separately are unknown due to lack of follow-up data. We aimed to evaluate the impact of transient hypothyroidism on increasing incidence of CH and to determine the natural course and the clinical, biochemical, and imaging characteristics of transient CH.Methods: Baseline and follow-up data of the infants with CH detected at screening in six provinces in the Black Sea Region were analyzed retrospectively during a time period covering the years 2008-2010.Results: Among 138 cases (48% female), 16 (12%) showed transient hyperthyrotropinemia which resolved without intervention. Of the treated 122 cases, 63 (52%) had transient CH. While its frequency was 35% in 2008, it increased to 56% in 2009-2010, following a lowering of the thyroid stimulating hormone cutoff value. The frequency was higher in inland provinces than in coast (67% vs. 43%; p=0.01).Clinical characteristics of permanent and transient cases were similar except female-to-male sex ratios (1.5:1 vs. 0.6:1; p=0.02). L-thyroxine was discontinued in 70% of transient cases before 3 years of age at a median age of 19 (2-36) months. The only indication for early discontinuation of treatment was a low L-thyroxine dose, which was 1.25±0.27 µg/kg/day at withdrawal time.Conclusion: Our regional follow-up data showed that more than half of newborns with primary CH had transient thyroid dysfunction. In the majority of cases, discrimination between transient and permanent CH can be made before age 3 years, as indicated by cessation of L-thyroxine treatment.

Impact of Lower Screening TSH Cutoff Level on the Increasing Prevalence of Congenital Hypothyroidism

“…A similar finding was reported from Italy, for a period of 20 years [6]. Kara [10]. In general, lower cutoff levels in screening programs have led to an increase in the proportion of detected cases of transient hypothyroidism, leading to an increase in the overall prevalence of primary CH.…”

“…However, it was not in accordance with some reports stating that transient and permanent forms of CH have contributed jointly to the increased CH prevalence [10]. The increased prevalence of CH after reducing the cutoff point is not necessarily a single predictor of transient TSH elevation [3], but in our case the prevalence of transient CH increased more than 8-fold.…”

“…The increased prevalence of CH after reducing the cutoff point is not necessarily a single predictor of transient TSH elevation [3], but in our case the prevalence of transient CH increased more than 8-fold. Similarly, an approximate 5-fold increase in the prevalence of transient CH has been reported in Turkey after reducing the cutoff point (1/1154 vs. 1/6202) [10,20]. The percentage of transient CH within the entire CH group revealed in our study showed an increment from 5.5% of all CH to 29.2%, indicating the important contribution of the lower TSH cutoff level in detecting additional cases of transient CH.…”

“…The majority of cases detected using a lower TSH cutoff tend to have milder hypothyroidism, with imaging often demonstrating an eutopic, "gland in situ". However, some cases turn out to have transient CH [5,7,[9][10][11].…”

Impact of Lower Screening TSH Cutoff Level on the Increasing Incidence of Congenital Hypothyroidism

“…Majority of cases detected using lower TSH cutoff tend to have milder hypothyroidism, with imaging often demonstrating an eutopic, "gland in-situ". However, some cases turn out to have transient CH [5,7,[9][10][11].…”