Low TSH and T4 in child

[kimdee]

My one year old son has slow motor skill development and has been seeing a neurologist. Blood tests were done and his TSH and T4 are both low. Not extremely low, but below what is normal. He had an MRI done yesterday of the brain, pituatry and hythmalus (sp.) and so far it looks good.

The doctors at this point don't seem overly concerned about this bloodwork, but it is really bugging me. Any ideas on why both numbers would be low as opposed to one high and one low?

[Mark Lupo, M.D.]

This sounds like non-thyroid illness.  In other words, your son may have stress/illness related to the motor skill development and this may cause a slightly low TSH and T4.  Would repeat the levels in 4-6 weeks along with a T3 -- IF all are falling then would reconsider pituitary problems and see a pediatric endocrinologist for full evaluation.

[B_Johnson]

Depends how low.

Low TSH and T4 implies that the cause is either in the hypothalmus (not secreting TRH to stimulate the pituitary)or the pituitary (not secreting TSH to stimulate the thyroid to produce T4 (thyroid hormone)).  Low T4 would be expected because of low TSH.

Brain imagining was done to make sure that there are no structural abnormalities or tumor within the pituitary or hypothalmus that would result in decreased activity.

Thyroid replacement (depending on how low) is important in a developing child in order for proper development of the nervous and other systems.  Later in life thyroid hormone mainly serves to control metabolism.. but as a child it is very important.