Is it really secondary hypothyroidism?

[Nicholasmom]

My son was reffered to edocrinologist due to short stature at age 12 mos. He also is about 3 mos. delayed on gross motor skills and was sleeping 18 + hours/day. His bone age was estimated to be around 6 mos. However there was a discrepency as follows: lack of calcifications of the carpal area assessed to be 3 mos., metacarpals and phalangeals assesed to be 6 mos. and distal radius assessed to be 15 mos. In Feb.his TSH level was 1.24. A free T4 was not initially done. 2 weeks later his TSH was 3.97 5IU/mL and his free T4 was .5 ng/dL . At the time of the blood draw he was taking Amoxicillin for a strep infection.He was diagnosed with secondary hypothyroidism. Cortisol level was 5.6 ug/DL, ACTH 16 (11:29 a.m.) After being on 25mcg synthroid for 6 weeks his TSH is .05 and his free T4 is.9. MRI revealed normal pituitary/hypothalmus. At 6 mos age he had surgery for bilteral orciopexy and inguinal hernia repair. At 4 mos.age his LH was 1 MIU/ML and FSH GNDOTRP BLD was 1.1 MIU/ML. He then received 2 injections of HCG with no futher bloodwork since the Dr. felt the injections did stimulate some production in the testes that allowed some descent. Also he has remained in 5th percentile for weight and has had severe reflux. Zantac and  Prevacid didn't seem to help this. However, we have seen some considerable improvement since changing to solid foods and whole milk at 12 mos. After being ill recently( 3 days of running a temp) followed by a viral- type rash he had a 2-3 day period of weakness, yet he seemed very hyper. Constantly moving hands and feet like an infant does. Now he is behaving normally and has resumed his normal activity level while awake,but he is sleeping 16-18 hours/day again.Why would his TSH level double in 2 weeks time? Why the bone age discrepency? Are there other stimulation test or bloodwork to be done? Any explanations for the recent symptoms following virus? Not sure where to turn next.
Thanks!

[Deanna L Aftab Guy, MD]

alot of workup has been done, you need to stay in touch with your endocrinologist with these questions as well. Firstly, thyroid functions vary from lab to lab and if we tested ourselves we would find different numbers every time, all in normal limits though, his are all normal, the free T4 was low end of normal but he was sick at the time and his tsh was normal. The thyroid labs are not fixed, we have varying levels depending on when we took our medicine and our body's response. So comparing one test to another is not the best thing to do necessarily unless we are assessing a patients medication level. They treated him and repeat was normal range, therefore he is good on that end. Bone age is not very accurate at all under age 2, they have to do it of the knee, so do not pay much attention to that of a wrist under age 2 and a delay is good since he has room to grow. I would not do any stimulation testing or any other testing other than monitor his thyroid and growth velocity and once a year bone ages, or perhaps not again till he is two. The virus episode is unclear and definitely a question for your pediatrician.
Do not seek other specialists, just stick with your pediatrician and endocrinologist, if you are not seeing a pediatric endocrinologist(it sounds like you are) then ask for a referral if possible

[Nicholasmom]

What is the normal free T4 range for a 12 month old male? We used 2 different labs recently and one had .5 as the low end of normal and the other said .9. Why the 2 different numbers? Is it necessary to treat as secondary hypothyroidism with free T4 of .5 and TSH at 3.97? What are the mental implications of an infant with low free T4 if, it in fact, was considered low. Also looking back at decline in growth rate (length) and clinical signs of gross motor delay, it seems both issues began as I returned to work and stopped breast feeding and switched to formula at about 10 moths of age. Is this a coincidence?

[Deanna L Aftab Guy, MD]

Each lab has its different standards depending on its assay so one may have more sensitive test than the other and can measure lower normal range. Some labs are 0.7-1.7 ng/dl in a child over 10 days, our lab normal is as low as 0.5-this varies by gestational age of the child when looked at in the newborn period.
So the lab has its standards that are usually reported for the age of the child tested.
If the child has overt hypothyroidism like a high tsh and a very low T4 or free T4 and this is untreated for weeks to months this can indeed lead to growth failure, constipation, developmental delay and long term concerns for intellectual compromise.
This is not the case with the labs that I am seeing from your child. I would stick with your endo and let them discuss the labs and plan of care with you carefully. They will determine if and when treatment is needed and follow the growth every 4-6 months. Bone age can be repeated when he is 2 of the wrist.

[Nicholasmom]

Thanks for your help! It is reassuring to hear we are on the right track!