Definition
• Deficiency of thyroid hormone production and decreased end-organ action
• Acquired (presents >6 mo) or congenital; 1° (↓ glandular production) or 2° (central)
Epidemiology and Etiology (Pediatr Rev 2009;30:251)
• Congenital: Most commonly absence of thyroid or ectopic thyroid tissue (lingual thyroid). Most sporadic, only 10–15% 2/2 inherited defects. Infants can have goiter w/ or w/o hypothyroidism if mother has iodine excess or def
• Acquired: Hashimoto’s (chronic lymphocytic thyroiditis), most common in US; iodine deficiency is most common worldwide. Other causes: XRT, infiltrative dz, large hemangioendothelioma (↑ T4 to rT3 conversion)
• Pt at increased risk: Down syndrome, T1DM, Turner, Klinefelter
Clinical Manifestations (Pediatr Rev 2009;30:251)
• Congenital Hypothyroidism: W/o Rx results in MR, severe growth failure (cretinism)
• Neonates (1st 2 wk of life)
• Post-term and LGA, hypothermia, poor feeding, large fontanelles, protuberant abdomen, edema of hands, feet, eyelids, neonatal jaundice (prolonged)
• >1 mo: ↓ activity, lethargy, constipation, FTT, poor suck, resp distress, darkened and mottled skin (carotenemia)
• >3 mo: As above w/ macroglossia, myxedema, hoarse cry, umbilical hernia, poor linear growth (can be earlier in severe in utero hypothyroidism)
• Acquired hypothyroidism
• Classic symptoms: Growth delay, impaired school performance, sluggishness, cold intolerance, lethargy, constipation, dry skin, brittle hair, myalgias
• Onset 6 mo–3 yo: Hoarse cry, umbilical hernia, coarse facies, dry skin, dec in linear growth, constipation, pseudohypertrophy (inc size of arm/leg muscles)
• Onset in childhood: Classic sx rarely w/ precocious sexual development (thelarche w/o pubarche in girls or gonadarche w/o pubarche in boys)
• Onset in adolescence: Classic sx but w/ delayed puberty; girls may have galactorrhea
• Physical exam: Evidence of above; bradycardia, HTN, slowed DTRs, +/− myxedema (thickened, nonpitting edematous Δ’s in soft tissue)
• Often w/ palpable thyroid (goiter) can be sym or asym; firm gland in thyroiditis, nodular gland raises concern for neoplasm but it is rare in pediatrics
• Severe cases can progress to myxedema coma
Diagnostic Studies (Pediatr Rev 2009;30:251)
• TSH and free T4 diagnose majority of cases; if gland nonpalpable, consider thyroid U/S or I-123 or technetium scan to r/o absent or ectopic gland
• Infants: Newborn screens identify most babies. Most states use T4 with f/u TSH
• Newborn nml ranges differ from adults; vary w/ age, highest on DOL1 (see table in the next page: Esotrix normal values)
• If low T4 and nml TSH, retest and screen for TBG deficiency (check free T4) which does not require treatment
• If abnormal, can consider radionuclide scan (I-123/Tc) to look for thyroid tissue (considered optional in AAP guidelines)
• Older children, adults: Screen with TSH and free T4. If abn, check thyroid (antithyroid peroxidase Ab, antithyroglobulin Ab)
Treatment (Pediatr Rev 2009;30:251–258)
• Congenital: Rx w/ levothyroxine; in infants w/ low T4 and TSH > 40 mU/L treat immediately with 10–15 mcg/kg QD, do not wait for confirmatory lab results
• Parental instruction: Crush T4 tab and mix w/ human milk, formula, or water. AVOID soy or Fe supplements with med admin
• 10–20% will have transient hypothyroidism but all infants should be treated until 3 yo, then one can consider 1 mo trial off T4
• Check TSH/FT4 q1–2mo in 1st year, every 3 mo in 2nd yr, every 4 mo till 6 yr, every 6 mo until adult ht, then yearly. Goals: TSH < 5 mU/L, FT4 = 10–16 mcg/dL
• Acquired: Initial dose depends on etiology, age, gender, TSH, body weight. Avg starting doses: 50 mcg (younger child), 75–100 mcg (older child/adolesc & adult). Titrate to low-nml TSH
Complications (Pediatr Rev 2004;25:94)
• Hypothyroidism prenatally w/o perinatal Rx, or delayed/insufficient Rx in cong hypothyroidism results in impaired intellect
• Hypothyroidism >3 yo generally reversible w/ Rx unless symptomatic >1 yr → results in short stature; assoc w/ hyperlipidemia, anemia, SCFE, & chronic constipation w/o Rx. Treatment of longstanding hypothyroidism may not prevent adult short stature