Isolated TSH elevation >20 is usually treated.
True congenital hypothyroidism mostly dysgenesis, ie poorly formed gland, of which <2% have identified mutations (mostly thyroid peroxidise, thyroglobulin and TSH receptor proteins – EDTA sample, Dr Therese Bradley at SGH Genetics). May be due to dyshormonogenesis (10%, autosomal dominant, gland looks normal on scan), TSH Receptor defect. Do a Family History.
Mostly found on newborn screening now. Life long.
Placental thyroxine important, iodine too, on neonatal thyroid function. In the first 14/7 of life, high TSH/T4/T3 seen. Transient neonatal hypothyroidism seen, 25% of +ve guthrie tests!
If missed or untreated, classic signs are umbilical hernia, goitre, hoarse cry, coarse facies, Developmental Dysplasia of Hip!
SPEG recommend that all families should be given the opportunity for imaging, subject to availability, because more informative than blood tests alone, will aid in genetic counselling, likelihood of lifelong treatment if proven permanent CH, provides a useful guide as to thyroxine dose.
Combined isotope and ultrasound imaging (dual scanning) is preferred. Isotope scans should be performed by day 5 of start of treatment to ensure avoidance of false negatives due to TSH suppression (advisable to take thyroid function sample on day of scans to confirm reliability of results). Ultrasound may show an abnormal gland (dyshormonogenesis) or else agenesis (no gland). But in agenesis may be remnants of embryonic structural elements which can be mistaken for a gland – can persist into teenage years but max 5mm x 5mm!. Hence importance of supporting radio-isotope imaging. Experience of ultrasonographer important.
Some concern that thyroxine liquid not as consistent levels? Automatic script request from pharmacy, patient then notified when ready.
- Scottish guideline suggests typical doses at different ages, up to age 3, to encourage dose changes with growth rather than waiting till dose insufficient and hypothyroidism emerges (see table). Use TFTs to confirm compliance.
- Assess growth: weight, length until 2 years, then height, head circumference until 3 years
- Assess development – consider pre-school audiology (for subtle hearing impairment due to CH)
- Transition – patient education. Boys to GP (unless problems with control), girls – to adult endocrinology (for pre-pregnancy counselling).
Aim for fT4 > 15 pmol/l and TSH <5.0 mU/l
||LT4 dose (ug daily)
||LT4 dose (ug/kg/day)