Intellectual Outcome at 12 Years of Age in Children with Congenital Hypothyroidism
December 1, 1999 3 minutes read
Intellectual Outcome at 12 Years of Age in Children with Congenital Hypothyroidism
ABSTRACT & COMMENTARY
Synopsis: Children with congenital hypothyroidism have intellectual defects that may be related to the severity of the disease at birth and inadequate replacement therapy.
Source: Salerno M, et al. Intellectual outcome at 12 years of age in congenital hypothyroidism. Eur J Endocrinol 1999; 141:105-110.
The intelligence quotient (iq) of 40 children diagnosed as having congenital hypothyroidism by neonatal genetic screening was determined in follow-up studies when they reached 12 years of age using the Wechsler Intelligence Scale for Children-Revised and compared with a control group made up of their healthy siblings. The mean IQ score of the hypothyroid children was not significantly different from the control group (88.4 ± 13 vs 93.4 ± 10.7). However, 13 patients showed subnormal IQ scores that were significantly lower when compared with their siblings (72 ± 4.9 vs 86.7 ± 9.6; P < 0.0001). The low IQ scores were associated with lower serum concentrations of thyroxine at diagnosis, poor treatment compliance during follow-up, and lower familial IQ. Even though the mean IQ scores in patients with congenital hypothyroidism fall within the norm for a carefully selected, related control group, low performance on IQ testing may be present in infants with more severe hypothyroidism and in those with inadequate compliance with replacement therapy.
Comment by Myron Genel, MD, FAAP
Without question, one of the public health triumphs of the past 25 years has been the development and widespread application of newborn screening for congenital hypothyroidism. Early identification and the provision of appropriate replacement therapy with levothyroxine prevents the profound mental retardation that often occurred when the diagnosis relied on clinical symptoms and a high index of suspicion. While the advent of universal neonatal screening programs makes possible early diagnosis, optimal outcomes are dependent upon a number of other factors, as is illustrated by this Italian report of the intellectual outcome at 12 years of age in 40 children detected by a regional screening program. Of these 40 children, 13 had IQs less than 80; for the most part, these were infants with the most profound chemical hypothyroidism when detected. Overall performance IQs were less in the hypothyroid children compared to their siblings, even though, as a group, full-scale and verbal IQs were not significantly different. It is useful to note that therapy was not begun until a mean age of 28 days; optimally, this should be accomplished in half of this time. The starting dosage of levothyroxine, as recognized by Salerno and colleagues, was low, averaging 6.8 mcg/kg/d, whereas current recommendations are for dosages of 10-15 mcg/kg/d. Additional factors include compliance to a daily treatment regimen and the pervasive effect on child rearing of having a child with a chronic and potentially disabling condition. Operationally, screening programs have improved significantly in the past two decades. Even so, only with prompt treatment, adequate therapy, and compliance with a daily treatment program can the full benefits be achieved.
Children with congenital hypothyroidism diagnosed in the neonatal period:
a. have much lower mean IQ scores compared to the mean IQ of a control group consisting of their healthy siblings.
b. have significantly lower IQs when compared individually to their healthy siblings.
c. IQ scores were lowest in children with relatively mild chemical indicators of hypothyroidism.
d. should be treated with 6 mcg/kg/d of levothyroxine.
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