Hypothyroidism%20(pediatric) Diagnosis
Classification
Differentiating Between Primary, Central and Subclinical Hypothyroidism
- Overt primary hypothyroidism: Low free thyroxine (FT4) and elevated serum thyroid-stimulating hormone (TSH)
- Subclinical primary hypothyroidism: Elevated TSH and normal FT4
- Repeat thyroid function test should be done after 3-6 months to confirm the diagnosis
- Central hypothyroidism: Low FT4 and low, normal or mildly elevated serum TSH
History
- Prolonged gestation
- Maternal history of thyroiditis (transient neonatal hypothyroidism)
- Maternal exposure to radioiodine or intake of goitrogens (eg Amiodarone, antithyroid drugs)
- Family history of hypothyroidism
- Thyroid treatment for hyperthyroidism (eg Thionamides, radioiodine or surgery)
- Viral infection followed by a painful thyroid gland with signs and symptoms of hyperthyroidism, later on manifesting signs and symptoms of hypothyroidism (subacute thyroiditis)
- Iodine sources (Iodine deficiency/endemic goiter)
- Excessive iodide intake (eg Kelps, radiocontrast dyes)
- Intake of goitrogens (eg Lithium, Amiodarone, thionamides)
- Head and neck radiation
Laboratory Tests
- Patient’s age must be considered in the interpretation of thyroid function results
Confirmation of Hypothyroidism
- Serum thyroid-stimulating hormone (TSH): Most valuable test for detecting hypothyroidism
- Free thyroxine (FT4) levels also useful for confirmation
- TSH and FT4 concentrations are higher in children, especially in the 1st week of life and throughout the 1st year
Other Thyroid Tests
- Thyroid autoantibodies: Antithyroid peroxidase and antithyroglobulin autoantibodies
- Thyroid scan, ultrasound
- Fine needle aspiration (FNA): Recommended for all palpable solitary or dominant nodules, independent of size
- FNA is preferred over thyroid scan or ultrasonography as the initial diagnostic test for thyroid nodules, although a previous ultrasound may aid the physician in performing the aspiration
Evaluation
Acquired Hypothyroidism
- If suspected, the entire function of the hypothalamic-pituitary axis should be evaluated with appropriate tests
- Once confirmed imaging studies of the brain and pituitary gland should be performed
Congenital Hypothyroidism
- Most infants appear unaffected at birth; signs and symptoms may be delayed until 6-12 weeks of age or older
- Newborn screening for congenital hyperthyroidism is crucial for early detection and treatment
- Delaying treatment after 6 weeks of life is associated with increased risk of delayed cognitive development
- Abnormal laboratory results must be communicated immediately so that empirical thyroid hormone replacement can be initiated even while waiting for confirmatory studies
Imaging
- Cranial imaging such as magnetic resonance imaging (MRI) is recommended in patients with confirmed central hypothyroidism
- Present or absent femoral/tibial epiphyses in radiographic imaging of the knee may help assess the severity of intrauterine hypothyroidism
- Scintigraphy and ultrasonography may also be used to assess the patient’s thyroid function and cause of the disease
- Performing both scintigraphy and ultrasound is highly suggested in neonates with high thyroid-stimulating hormone (TSH) levels
Screening
Newborn Screening for Congenital Hypothyroidism
- Goals of screening: To identify and treat patients at risk for the health consequences of thyroid dysfunction before they become clinically apparent
- Additional indications and ideal time for screening:
- Normal hospital delivery at term: 2-4 days of age
- Infants in neonatal intensive care units (NICU), preterm babies, home births: Within 7 days of age
- Maternal history of thyroid medication or family history of congenital hypothyroidism: Cord blood for screening
Types of Newborn Screening
- Primary thyroid-stimulating hormone (TSH), backup free thyroxine (FT4): May miss thyroid-binding globulin deficiency, central hypothyroidism, hypothyroxinemia with delayed TSH elevation
- Primary T4, backup TSH: May miss delayed TSH elevation with initial normal T4
- Primary T4 and TSH: Ideal screening approach
Interpretation of Newborn Screening Results
- Elevated TSH and low T4: Congenital hypothyroidism
- Normal TSH and low T4: Transient hypothyroxinemia, central hypothyroidism, thyroid-binding globulin deficiency, isolated low T4
- Elevated TSH and normal T4: Transient/permanent mild congenital hypothyroidism, delayed maturation of hypothalamic/pituitary axis, thyroid hormone resistance, Down syndrome, subclinical hypothyroidism
- Delayed TSH elevation and low T4: Low or very low-birth weight infants, preterm infants, sick term newborn
Confirmation of Results
- Infants with abnormal or borderline screening results should have free T4 and TSH drawn for definitive testing
- Thyroid hormone replacement may be empirically initiated while awaiting confirmatory results
Secondary Screening for Congenital Hypothyroidism
Recommended for the following:
- Preterm neonates
- Infants with low-birth weight (LBW)
- Infants with very low-birth weight (VLBW)
- Unhealthy infants/preterm neonates previously admitted in the NICU
- Newborn screening done within 1st 24 hours after birth
- Multiple pregnancy