Lab test essential. A child with hypoactive thyroid may have constipation, delayed growth, poor cognitive skills, large tongue etc. However, clinical signs and symptoms are not a good indicator of thyroid function. If there is any doubt, easily available and not too expensive tests, e.g., TSH and free T4 are essential for a proper work-up.
Symptoms. Depending on the age of the child and severity of the hypothyrodism: constipation, abdominal pain, fatigue, dry skin/hair, feeling cold, growth failure, sore joints. Infants born with this may have unique symptoms. It is medically urgent to identify newborns with underactive thyroid because thyroid hormone is integral to normal brain development in infants and kids under 2 years old.
Hypothyroidism. Similar to adults with 2 major exceptions: often hypothyroidism leads to failure to thrive or lack of weight gain vs adults which usually causes weight gain. Secondly, poor growth is often seen. Other symptoms like fatigue, dry skin, coarse hair, hair loss, forgetfulness, moodiness, constipation, cold intolerance, and exercise intolerance are similar to adults.