Severe hypothyroidism and slow onset of
adequate treatment are associated with learning and memory deficits
in children with congenital hypothyroidism
(March 2002)
The background of
the study. Early treatment of children with congenital hypothyroidism
prevents the developmental delay associated with later treatment,
but some children treated early have cognitive impairment, including
limitations in attention, language, and memory. This study evaluated
the relationships between specific cognitive abilities and the severity
and adequacy of treatment of children with congenital hypothyroidism.
How the study was done. The study
subjects were 62 children 7 to 12 years old who had congenital hypothyroidism
detected by neonatal screening between 1986 and 1992. Among them,
18 had no thyroid tissue (athyreosis), 27 had abnormally located
thyroid tissue, and 17 had normally located thyroid tissue. On average,
thyroxine (T4) treatment was initiated 17 days after birth; the
initial dose was 9 µg/kg/day.
The tests done for the study included the Vocabulary, Arithmetic,
Coding, and Symbol Search subtests of the Wechsler Intelligence
Scale for Children, and the Children's Memory Scale.
The results of the study. The clinical
characteristics, serum thyrotropin (TSH) concentrations, and initial
doses of thyroxine were similar in the children with the three different
types of thyroid disease.
The children in the athyreosis group were less likely to have normal
serum TSH concentrations during the first three months of treatment,
and their dose of T4 was adjusted more often during the first year
of treatment, as compared with the other two groups. These children
scored lower on many components of the Wechsler Intelligence Scale
for Children, whereas the scores for the other two groups were similar.
The scores on these tests and the Children's Memory Scale were lower
in all children who had high serum TSH concentrations during the
first three months of treatment, as compared with the children with
normal concentrations at these times.
The conclusions of the study. Among
children with congenital hypothyroidism, those with athyreosis and
those in whom treatment does not lower TSH secretion quickly are
at increased risk for learning and memory deficits later in life.
The original article. Song S-I,
Daneman D, Rovet J. The influence of etiology and treatment factors
on intellectual outcome in congenital hypothyroidism. J Dev Behav
Pediatr 2001;22:376-84.
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