hypothyroidism%20(pediatric)
HYPOTHYROIDISM (PEDIATRIC)
Hypothyroidism is due to decreased or absent production of thyroid hormone.
Primary hypothyroidism is caused by generalized tissue resistance to thyroid hormone and disorders that affect the thyroid gland directly. It is responsible for majority of hypothyroid cases.
Central hypothyroidism is caused by hypothalamic or pituitary disorders.

Follow Up

  • Treatment adequacy is monitored by measuring serum free thyroxine (FT4) & thyroid-stimulating hormone (TSH) levels
  • T4 dose adjusted by 25-50 mcg increments based on the serum TSH level measured 2-4 weeks after starting treatment & every 4-6 weeks thereafter until normal TSH is reached
    • In children, serum TSH & FT4 levels should be assessed based on age-specific & method-specific reference ranges
  • Once a target level of serum TSH is reached, measure TSH & FT4 levels every 2-3 months, provided that no other medications are taken that may change the bioavailability or absorption of the T4
    • When patient has to switch to a different T4 brand, serum TSH must be checked 2-4 weeks later, then doses adjusted accordingly
    • Intake of other medications that may alter T4 bioavailability warrants rechecking of serum TSH after 4-6 weeks & adjusting of T4 doses if needed

Considerations

Central hypothyroidism

  • TSH is not used as a marker of adequate treatment
  • Serum FT4 is a useful index

Congenital hypothyroidism

  • Infants are monitored frequently in the first 2 years of life using serum TSH as primary parameter & FT4 as the secondary parameter, employing age-appropriate reference intervals
  • During the 1st year of life, total T4 & FT4 is maintained in the upper half of the normal reference range
  • Monitoring:
    • Recheck T4, TSH
    • 2-4 weeks after initial treatment has begun
    • Every 1-2 months in first 6 months of life
    • Every 3-4 months between 6 months-3 years of age
    • Every 6-12 months from 3 years of age until end of growth
    • For patients suspected of treatment noncompliance or w/ abnormal lab results, monitor more frequently
    • Obtain FT4 & TSH measurements 4-6 weeks after T4 dose adjustments
    • Blood samples for FT4 & TSH measurements should be collected ≥4 hours after T4 intake
  • Several studies have suggested monthly monitoring for patients w/ the following:
    • Dose adjustment w/in 1 month from prior visit
    • Total T4/FT4 measurements w/in the lower half w/in 1 month from prior visit
    • TSH of 5-10 mU/ml & total T4/FT4 measurements w/in the lower half w/in 1 month from prior visit
    • TSH >10 mU/ml w/in 1 month from prior visit, even if total T4/FT4 levels are in the upper limit of normal
    • TSH <0.1 mU/ml
  • Assess permanence of congenital hypothyroidism
    • If initial thyroid scan shows ectopic/absent gland, congenital hypothyroidism is permanent
    • If initial TSH is <50 mIU/L & no increase in TSH after newborn period, then trial off therapy at 3 years of age
    • If TSH increases off therapy, consider permanent congenital hypothyroidism
    • Should be performed in children >3 years
  • If circulating T4 levels remain persistently low & TSH remains high despite progressively larger replacement doses of T4, it is important to determine the possibility of poor compliance
    • The most frequent reason for failure to respond to replacement therapy has been interference w/ adsorption by soy-based formulas or w/ medications that contain iron

Thyroid Re-evaluation

  • Thyroid axis re-evaluation should be done 4-6 weeks after temporary withdrawal of treatment in patients ≥ 3 years of age
  • May be performed in patients <3 years w/ occassional increased TSH levels (eg positive TSH receptor antibodies, eutopic thyroid gland seen on imaging)
  • Indicated for the following:
    • If not done during infancy
    • Child was born preterm or ill during initial evaluation & treatment
    • Patients w/o known enzyme defects
    • Normal goiter w/ or w/o goiter at initial evaluation
    • Neonates w/ positive thyroid antibodies
    • Patients w/o dosage increase/adjustments since start of treatment
  • Should be deferred for those:
    • W/ diagnosed thyroid ectopy, apparent athyreosis, or true athyreosis via imaging
    • Diagnosed w/ dyshormonogenesis via genetic testing
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