A 5.5-year-old girl was diagnosed with primary CH through screening at the age of 2 weeks. She was a firstborn child of young, healthy parents. The child was delivered after 39 weeks of gestation with forceps-assisted vaginal delivery. The anthropometric parameters were adequate for the gestational age. The Apgar score was 5 and 7 in the first and fifth minute, respectively; thus, initial oxygen stabilization was required. The heel-prick blood test for CH screening performed 72 h after birth showed an elevated TSH value of 12.3 mIU/L (DELFIA neonatal TSH, LKB). Confirmatory serum tests performed at 14th postnatal day (IMMULITE 2000 chemiluminescent enzyme immunoassay system; Siemens Healthcare Diagnostics Inc., NY, USA) showed high TSH level, 30.9 mIU/L (normal: 0.4-5.0 mIU/L) and low T4, 4.38 microg/dL (normal: 6.4-13.3 microg/dL). Ultrasound examination revealed no visible thyroid gland in the usual position and the patient was diagnosed with primary CH due to TD. Therapy with levothyroxine (10.5 microg/kg/day) was initiated and thyroid hormone levels normalized within 2 weeks. The patient was subsequently followed up at 3-month intervals. Several higher values of TSH were noted (up to 6.19 mIU/L). After the first year, she remained euthyroid with a levothyroxine dose tapered down to 1.8 microg/kg/day. Results of thyroid tests and levothyroxine dose during the follow-up are presented in Table 1. The growth and neurodevelopment were completely normal. At the age of 3 years, after several consecutive normal serum thyroid results, the levothyroxine dose was gradually decreased and then discontinued at the age of 3.5 years. At this point, she was lost from follow-up.
After 2 years off therapy (at the age of 5.5 years), the girl was referred for investigation of anemia with the following blood counts: hemoglobin (Hb), 10.0 g/dL (normal: 11.5-14.0 g/dL); red blood cell count (RBC), 4.98 x 106/microL (normal: 4.0-5.3 x 106/microL); serum iron, 3.7 micromol/L (normal: 6.6-26 micromol/L). Her height and weight were on the 50th percentile for age, there were no signs of clinical hypothyroidism, and she had normal neurocognitive development. The thyroid testing showed mildly elevated TSH (7.8 mIU/L) and low FT4 level 0.856 ng/dL (normal: 0.89-1.76 ng/dL). Thyroid peroxidase (TPO) antibodies were within normal range, 20 IU/mL (reference range: 10-35 IU/mL).
Ultrasonographic investigation of the neck (Figure 1) detected no thyroid tissue at the normal pretracheal thyroid location but presence of submentally located oval formation (12 mm x 18 mm) of iso- and hypoechoic, nonhomogeneous thyroid-like tissue, mostly with peripheral vascularization.
A thyroid scan was performed by a double-head Mediso gamma camera after an intravenous injection of 99m-technetium pertechnetate (2 MBq/kg), and standard images (anterior, lateral) were obtained in supine position. Scintigraphy showed ectopic thyroid tissue located submentally without any uptake in the normal thyroid location (Figure 2). Magnetic resonance imaging (MRI) showed marked round formation in the submental region, in the projection of the floor of the mouth (Figure 3). The follow-up thyroid hormone tests after 1 month were consistent with subclinical hypothyroidism; thus, low dose levothyroxine was re-introduced. Furthermore, close thyroid follow-up is scheduled to access child's need for therapy and dose adjustment.