On this page
Study tools
Write your answer
Saved on this device. No marking — you are the marker.
Stem
A 12-day-old term female infant is referred by the newborn screening laboratory with a heel-prick TSH of 96 mU/L (cut-off 20 mU/L) taken on day 5. In clinic she is mildly jaundiced, feeds sluggishly, has a large posterior fontanelle, a protuberant abdomen with an umbilical hernia, and a 1 cm palpable mass in the neck midline. Mother has a history of Graves' disease, currently in remission on no medication. Venous samples have been sent.
Questions
a) Diagnosis and immediate management? (2 marks) Diagnosis: congenital hypothyroidism (primary) — elevated newborn-screen TSH with compatible clinical features. Immediate management: start levothyroxine 10 to 15 mcg/kg/day orally, once daily, the same day — treat first, investigate later; do not wait for venous results, ultrasound, or scintigraphy. Reassure parents and refer to paediatric endocrinology.
b) What three bedside findings are most characteristic of neonatal CH, and why is she only mildly symptomatic? (3 marks) Characteristic: prolonged (unconjugated) jaundice, large posterior fontanelle (over 5 mm at term), umbilical hernia with macroglossia, hypotonia and hoarse cry. She is only mildly symptomatic because maternal thyroxine crosses the placenta and sustains fetal/neonatal levels for the first weeks; clinical signs emerge as maternal T4 is metabolised — which is exactly why universal newborn screening is essential (clinical detection alone is too late).
c) Confirmatory and classifying investigations? (3 marks) Confirm: venous TSH (high) and free T4 (low) — the diagnostic pattern of primary CH (reference ranges are age-specific). Classify the cause (after treatment started): thyroid ultrasound and technetium-99m or iodine-123 scintigraphy to localise the gland (ectopic, absent, or in-situ goitre — the midline mass here may be ectopic thyroid). Maternal TSH-receptor antibodies (her Graves' history raises the possibility of transient maternal-blocking-antibody CH). Bone age X-ray (knee/foot) gauges severity. Genetic tests if dyshormonogenesis or Pendred suspected. Note: central CH (low TSH + low free T4) is missed by TSH-only screening.
d) Monitoring schedule and the role of re-evaluation at age 3? (2 marks) Monitor TSH and free T4 at 2 and 4 weeks, then every 1 to 2 months in the first year, every 2 to 3 months in the second, every 3 to 12 months thereafter, and 4 weeks after any dose change. Target: free T4 upper half of the age-specific range, TSH 0.5 to 5 mU/L. At age 3 (after the critical neurodevelopmental window) perform a trial off levothyroxine for 4 to 6 weeks and recheck — rising TSH/falling free T4 confirms permanent CH (lifelong treatment); persistent normal values indicate transient CH (common with maternal blocking antibodies) and treatment can stop.
Marking guide
- a (2): diagnosis 1 mark; levothyroxine 10 to 15 mcg/kg/day immediately + treat-first principle 1 mark.
- b (3): three characteristic signs 1.5; reason (maternal T4 transplacental) 1; link to screening rationale 0.5.
- c (3): venous TSH + free T4 1; ultrasound + scintigraphy 1; maternal antibodies (+ genetics/bone age) 1.
- d (2): monitoring schedule 1; age-3 trial-off-treatment to distinguish permanent vs transient 1.