To the Editor: We report an acute presentation of congenital hypothyroidism in a child almost 6 years old. The condition was not detected by newborn screening.

Screening of all neonates started in New South Wales in July 1977, with thyroid stimulating hormone (TSH) being measured in dried blood spots taken from a heel-prick blood sample (currently at 2–3 days of age). A whole-blood TSH level of 40 mIU/L or above triggers a request for full thyroid function testing, whereas with a level of 20–39 mIU/L a second sample is requested. We have screened over 2.3 million babies and detected 690 babies with congenital hypothyroidism. Ten babies with dyshormonogenesis or ectopic thyroid tissue had normal results and were missed by the screening test. Since screening started, “juvenile hypothyroidism” not associated with thyroid antibodies has all but disappeared.

A healthy girl aged 5 years 11 months presented with acute dysphagia and drooling. There were no previous dysphagic symptoms. Initially, epiglottitis was suspected; however, at endoscopy a lingual thyroid was visualised at the base of her tongue, and this was confirmed by a technetium scan. She had normal growth and development, with both height and weight at the 50th centiles, a pulse rate of 90 beats/min, and normal deep tendon reflexes.

The whole-blood TSH level at newborn screening on Day 3 was 40 mIU/L (reference range [RR], < 20 mIU/L). Thyroid function testing at another hospital on Day 10 showed a serum TSH level of 16.6 mIU/L and a serum free thyroxine (FT4) level within the normal range (12 pmol/L; RR, 11–30 pmol/L). These results were interpreted as normal, whereas, in fact, the TSH level was above the reference range for 10 days of age (< 10 mIU/L), although within the reference range for 2–7 days.

On the patient’s admission for treatment of acute dysphagia, the TSH level was 10.9 mIU/L and the FT4 level was 18 pmol/L. A diagnosis was made of compensated hypothyroidism secondary to the ectopically placed lingual thyroid. Thyroxine treatment was commenced on diagnosis, and regular follow-up arranged. Three months after the start of treatment, the results of thyroid function tests (FT4, 17 pmol/L; TSH, 2.7 mIU/L) were within the normal range.

Acute presentation of a lingual thyroid is most unusual.1 This case emphasises that further investigations must be performed when thyroid function test results are equivocal. Unfortunately, the thyroid status was considered normal because the FT4 value was within the normal range. All babies whose TSH results remain elevated while the FT4 levels are normal should have a thyroid scan, as we recommend when reporting results.