Prepubertal and pubertal growth, timing and duration of puberty and attained adult height in patients with congenital hypothyroidism (CH) detected by the neonatal screening programme for CH--a longitudinal study

Abstract

Objective: We have evaluated parameters of growth, the pubertal process and attained adult height in patients with congenital hypothyroidism (CH) of various aetiologies, diagnosed by the neonatal screening programme, and followed up longitudinally. To the best of our knowledge, no such data are available in the published literature. Our aim was to define the most important factors affecting these parameters.

Patients and measurements: Thirty patients with CH (20 females and 10 males) diagnosed by neonatal screening (dysgenetic (n = 15), ectopic thyroid (n = 11), and enzymatic defect (n = 4)), treated with levo-thyroxine (L-T4) since the age of < or = 4 months, and followed up at intervals of 1-6 months for a mean period of 11.4 (range 5-19.6) years were evaluated. Detailed anthropometric measurements were performed by the same trained nurse, and pubertal stages were evaluated according to Tanner's criteria for breast or genitalia and pubic hair. Serum T4 and TSH levels were measured at each clinic visit using commercial kits. Bone age (BA) was determined at 6-12 months intervals using the Greulich & Pyle method. Seventeen patients attained adult height at the time of the report.

Results: Mean L-T4 dose of 7.9 (range 5.2-14.0) to 2.4 (range 1.3-3.4) micrograms/kg/day at various ages corrected the serum free T4(f-T4) levels to normal (> 10 pmol/l) in 95% of determinations, and the TSH level was reduced to < 10 mIU/l in 54% of the determinations during the follow-up period. Length at initiation of therapy (mean -0.15, (range -2.5-2.1) SDS), height at onset of puberty (mean -0.4, (range -1.8-1.8) SDS) and adult height (mean 0.2 (range -1.4-2.0) SDS, n = 17) were within the normal range (0.00 +/- 2 SDS). Onset and duration of puberty were normal in both sexes, and total pubertal growth contributed 19.1% (M) and 16.4% (F) to adult height. Peak height velocity (mean 10-6 (range 7.3-15.1) (M) and mean 8.0 (range 6.2-15.5) (F) cm/year) was within the normal range and occurred at the expected BA (14y; M and 12y; F). The attained average adult height was in close proximity to the average target height in both males and females. A significant positive correlation was found between the average L-T4 daily dose administered during the first 6 months of treatment and the attained adult height.

Conclusions: Early detection by neonatal screening and treatment of congenital hypothyroidism enables normal prepubertal and pubertal growth and achievement of normal adult height, following normal puberty. Adult height in congenital hypothyroidism is significantly correlated with parental height and the mean L-T4 daily dose administered over the first 6 months of treatment. A dose of at least 8.5 micrograms/kg/day is recommended during this period. Periodical adjustments of L-T4 daily dose should be guided by clinical observation and serum free T4 levels.