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- What are the causes of lack of “ catch - up growth ” in a child with juvenile hypo-
thyroidism who is on optimal L - thyroxine replacement?
Failure to have a catch-up growth despite optimal L-thyroxine replacement
in children with juvenile hypothyroidism should raise a suspicion of coex-
isting disorders like celiac disease, Turner syndrome, or growth hormone
defi ciency. - How to treat and monitor juvenile hypothyroidism?
The recommended dose of L-thyroxine is higher in children as compared to
adults due to larger body surface area (in relation to body weight) and increased
clearance of thyroid hormones in children. The recommended daily dose of
L-thyroxine in children aged 1–5 years is 5 μg/Kg, while it is 4 μg/Kg in those
between 6 and 12 years of age, and 3 μg/Kg in those aged >12 years, who have
not completed the puberty. However, in postpubertal children L-thyroxine should
be administered at dose of 1.6–1.8 μg/Kg/day. Both T 4 and TSH should be moni-
tored till 3–4 years of age; TSH should be maintained in the lower half of normal
reference range (0.5–2.5 μIU/ml) and T 4 in the upper half of normal reference
range. Thereafter, TSH alone can be monitored every 3–6 monthly and main-
tained between 0.5 and 2.5 μIU/ml. Adverse effects are rare with L-thyroxine
therapy and include pseudotumor cerebri, craniosynostosis, acute psychosis, and
decline in scholastic performance. Bone age should be reassessed, if required.- What is the outcome of complications related to long - standing juvenile
hypothyroidism?
Long-standing severe juvenile hypothyroidism is associated with short stature,
delayed puberty, thyro-lactotrope hyperplasia, multicystic ovaries, precocious
puberty, pseudo-myohypertrophy, epiphyseal dysgenesis, and slipped capital
femoral epiphysis. Most of these manifestations usually reverse within 3–6 months
of optimal L-thyroxine replacement. Although height improves after L-thyroxine
therapy, fi nal adult height is often subnormal in those with long-standing juvenile
hypothyroidism. Stippled epiphysis normalizes with L-thyroxine therapy but
slipped capital femoral epiphysis need surgical intervention. - Why are clinical manifestations less severe in children with secondary
hypothyroidism as compared to those with primary hypothyroidism?
Secondary hypothyroidism is characterized by low FT 4 and low/normal to
mildly elevated TSH. Clinical manifestations are less severe in children with
secondary hypothyroidism as compared to those with primary hypothyroidism.
This is because T 4 defi ciency is usually mild in secondary hypothyroidism due
to ongoing TSH-independent T 4 synthesis, which contributes to 10–15 % of
circulating T 4. In addition, presence of concurrent multiple pituitary hormone
defi ciencies may mask the features of hypothyroidism. However, in primary
hypothyroidism T 4 defi ciency is usually severe, and markedly elevated TSH
contributes to myxedematous manifestations.
3 Thyroid Disorders in Children