Occasionally, however, I see a report in the literature about a patient with hypothyroidism masked by Down's syndrome. This points out the need to keep one's diagnostic skills honed in order to pick up the occasional hypothyroid infant or young child who may have escaped detection. The hypothyroid newborn can present with a wide range of symptoms that might be attributed to various other disorders. As time passes one may also notice macroglossia, umbilical hernia and patent fontanelles. Other skeletal effects of overdosing are closure of epiphyses and possible osteoporosis.
Overtreated infants are irritable, nervous and have problems gaining weight.
Chronic under-replacement retards physical and intellectual growth and poses all of the eventual problems consistent with hypothyroidism. Neonatal titration . I see the patient and monitor T4 and T3 resin uptake, and run a highly sensitive TSH assay every 1 to 2 months in the first year and every 3 to 4 months during the second year, the period of exceptionally rapid growth and hormone demand. There is recent evidence that small and transient variations in highly sensitive TSH concentrations are not particularly significant. The hypothyroid child may be protected against overtreatment by increased deiodination of thyroxine to the relatively inactive reverse triiodothyronine instead of to triiodothyronine, which appears to be the most important in regulating TSH levels.