Congenital Hypothyroidism and Thyroid Cancer

Abstract

Congenital hypothyroidism (CH) is a condition of thyroid hormone deficiency present at birth and can result in severe neurodevelopmental impairment, growth failure and permanent mental retardation if treatment is delayed for several months after birth (1-3). Girls are more frequently affected than boys (female to male ratios ranging from 2:1 to 4:1)(4). The mental retardation and neurodevelopmental impairment include poor motor coordination, ataxia, spastic diplegia, muscular hypotonia, strabismus, learning disability and diminished attention span (5). Consequently, most countries operate neonatal screening programs to enable early detection of cases and therapeutic intervention. Treatment consists of a daily dose of thyroid hormone (thyroxine) by mouth (6, 7). Because the treatment is simple, effective, and inexpensive, nearly all of the developed world practices newborn screening to detect and treat CH in the first weeks of life. The diagnosis is based on the measurement of TSH on the second or third day of life. If the TSH is high, the infant's doctor and parents are called and a referral to a pediatric endocrinologist is recommended to confirm the diagnosis and initiate treatment (6). Often a technetium (Tc-99m pertechnetate) thyroid scan is performed to detect a structurally abnormal gland. The Tc-99m pertechnetate exam will help differentiate thyroid dysgenesis from thyroid dyshormonogenesis. Most children born with CH and correctly treated with thyroxine grow and develop normally in all respects. Even most of those with athyreosis and undetectable T4 levels at birth develop with normal intelligence. However, in some cases mild learning problems, subtle neurological dysfunctions, and subnormal IQ have been reported (2, 5). In a 5 year followup study of children with CH, Arenz et al reported that children with an initial thyroidstimulating hormone (TSH) value of >200 mU/L performed significantly worse in motor skills than children with TSH value of < or =200 mU/L although intellectual development was normal (8). Glorieux et al reported that 27 patients with congenital hypothyroidism diagnosed by neonatal screening were examined at the age of 12 years. The 12 patients with severe hypothyroidism at diagnosis (thyroxine < 26 nmol/L, and area-of-the-knee epiphyses < 0.05 cm2) had a lower IQ than the 15 patients with less severe hypothyroidism (9). Salerno et al evaluate the intellectual outcome in 40 12-year-old patients with CH detected by neonatal screening, 13 patients showed subnormal IQ score (72.4+/-4.9) compared with their siblings (86.7+/-9.6; P<0.0001) and with the other patients (96.1+/-9.6; P<0.0001). The low IQ score was associated with lower serum concentrations of thyroxine at