Growth prognosis and growth after menarche in primary hypothyroidism

The long term growth of 20 girls and nine boys with juvenile primary hypothyroidism was studied until they reached final height. At diagnosis the girls had a mean age of 8.8 years (range 3.0-13.0); mean bone age was 5.4 years. The mean age of the boys at diagnosis was 9.5 years (range 3.7-14.2); mean bone age was 6.3 years. The patients were treated with thyroxine 100 micrograms/m2/day and serum thyroxine concentrations were maintained in the normal range. During treatment the rate of skeletal maturation exceeded the change in chronological age. Initial mean height SD score for bone age before treatment in the girls was +0.59 and after 11 years of treatment fell to -0.55 Mean height SD score for bone age in the boys decreased from +1.6 to -0.87 during treatment. In the girls the onset of puberty was 1.2 years later than the normal population but the duration of puberty was reduced. Mean age (SD) of menarche was 13.8 (1.7) years. The pattern of growth in girls with treated hypothyroidism was abnormal as growth continued after menarche, at a time when normal girls have almost stopped growing. During the second year after menarche our patients still had a mean growth velocity of 4.1 cm/year. Our data suggest that juvenile primary hypothyroidism results in a permanent height deficit. In addition, there is a loss of the normal harmony between growth and sexual maturation in girls, despite adequate treatment, in that growth continues for much longer after menarche than in normal girls.