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The treatment of hypothyroidism with levothyroxine is guided by labwork.  You may have heard that treatment is based on symptoms or resolution of symptoms.  Though, it is important to note any changes in the symptom, the dose of the medication is mostly guided by your lab results.   There are several reasons for this.  First, the symptoms may not be related to hypothyroidism.  They may not resolve with treatment or normalization of the labs.  Increasing the dose based on symptoms alone may cause the levels to swing to the other extreme and cause hyperthyroidism.  The organs and body are seeing too much thyroid hormone and most likely will develop new problems such as difficulty sleeping, concentrating, growth issues, increased heart rate, sweating, and increased stool frequency.

In general there are guidelines on increasing the dose such that the levels the TSH is the low end of normal but not suppressed and the ft4 is at the upper end of normal.  In individuals who do not have a disorder of hormone production from the hypothalamus or pituitary the treatment goals are based on the thyroxine levels.

What medication to use?  Levothyroxine is the recommended medication.  It is given in tablet form and can be crushed for those children that are too young to swallow the tablet whole.  

Generic vs brand?  In general both generic and brand names contain the same active ingredient or medication but have different inactive ingredients.  Brand name medications cost more than generic medications.  Brand name medications pharmacokinetics though maybe different or have more reliable dosing.  In some instances, such as severe congenital hypothyroidism it might be recommended that brand name medication such as Synthroid be used instead of generic. 

Levothyroxine vs liothyronine?  Levothryoxine is activated into the active form or triiodothyronine.  In majority of individuals, providing thyroid hormone replacement in the form of levothryoxine will treat the hypothyroidism effectively.  In rare cases, your physician may determine that there maybe a benefit from adding T3 supplementation.

Dessicated thyroid hormone?  Desiccated thyroid hormone in not FDA approved to be used in in pediatric patients.  The pills do not have consistent dosing as they are derived from dried animal thyroid glands.  Each batch had different amounts of T4 and T3 making it harder to get the blood levels into the normal range.

Generic Levothyroxine Compared with synthroid in Young Children with Congenital Hypothyroidism. JCEM 2013

Carswell, J. M., Gordon, J. H., Popovsky, E., Hale, A., & Brown, R. S. (2013). Generic and Brand-Name l-Thyroxine Are Not Bioequivalent for Children With Severe Congenital Hypothyroidism. The Journal of Clinical Endocrinology and Metabolism, 98(2), 610-617. 

https://doi.org/10.1210/jc.2012-3125

https://www.thyroid.org/brand-generic-medication/

https://www.verywellhealth.com/levothyroxine-brand-name-vs-generic-versions-1124055

Congenital hypothyroidism (CH) is typically detected through the newborn screen.  The newborn screen is performed with a collection of heel prick obtained blood sample on special filter paper.  The newborn screen evaluates for several disorders in addition to congenital hypothyroidism.  The timing of the newborn screen is very important and needs to be done after 24 hours of life.  The reason for this is that there is a surge of thyroid stimulating hormone (TSH) that occurs shortly after birth.  The elevation in TSH that occurs in the first 24 hours can falsely make the screen positive.  Some states will also do a second screen between 10-14 days of life.  There are established norms of TSH values that take this into account along with prematurity after the first day of life.

The newborn screen is crucial since most babies born with congenital hypothyroidism do not display any obvious signs or symptoms at birth or shortly after birth.  If treatment is not initiated in a timely manner, the infant is at risk for developing sequelae of not having normal thyroid levels.  These include abnormal weight gain and linear growth, jaundice, anemia, decreased tone, delayed milestones, and intellectual disability.  All these can be avoided with timely diagnosis and initiation of treatment.

Which thyroid hormones does a newborn screen evaluate for?  There are several different types of newborn screening methods.  A newborn screen can evaluate and report TSH, total thyroxine, or both.  This will depend on which state does the testing.  Most states will screen with a TSH and secondarily report a T4 if the TSH is abnormal.

There will be a very small number of infants that will have a false negative on the newborn screen.  This means the infant has the diagnosis but it was not detected by the screen.  The following are risk factors that are associated with a false negative screen: preterm birth, low birth weight, same-sex twins, or family history of hypothyroidism.1  It would be advisable to obtain repeat thyroid function testing in these high risk infants.

What happens after your provider or medical team gets an alert for a positive screen from the state?  Your provider or medical team will contact you and arrange for your baby to get bloodwork tests to confirm the newborn screen results or a second newborn is performed.  In most places, there is a laboratory that is available that has a quick turnaround in results (within a day).  If the repeat labs are consistent with congenital hypothyroidism then you will be contacted by the provider to start treatment right away.  You will be counseled on the medication, how to take it properly, what to do when a dose is missed, what to avoid with giving the medications, and when to have blood work repeated to assess if the dose is adequate.

What happens if the test results are equivocal?  Your infant will undergo follow-up testing until the labs normalize or a decision is made to initiate medication.

Your primary care team will most likely refer your infant to a pediatric endocrinologist who specializes in thyroid disorders.

For more information on newborn screening or congenital hypothyroidism:

CDC:https://www.cdc.gov/newbornscreening/

https://medlineplus.gov/genetics/condition/congenital-hypothyroidism/

https://www.magicfoundation.org/

https://www.thyroid.org/

The state of Colorado: https://cdphe.colorado.gov/laboratory-services/newborn-screening

1.Zhejiang Da Xue Xue Bao Yi Xue Ban 2022 Jun 25;51(3):314-320. doi: 10.3724/zdxbyxb-2022-0213.

Case of Hypothyroidism Due to Iodine Deficiency:

Iodine deficiency is a common cause of hypothyroidism in third world countries in malnourished populations.  Its rare in the US but has been reported.  In this case was published in Nov2022, and it involved an adolescent with mild autism spectrum who had an extremely restricted diet.  He had an enlarged gland or goiter and had negative thyroid antibodies.  Testing revealed his body was iodine deficient.  His goiter and thyroid abnormalities resolved with iodine supplementation.

Risk factors for iodine deficiency:
Picky eater/food aversion
Mulitple food allergies
Vegan Diet
Autism Spectrum Disorder

Common sources of iodine:
Milk
Bread
Iodinized salt
Seafood

Recommended Dietary Reference Intakes (The Harriet Lane Handbook, 20th ed.)

Moore CE, Sasidharan Pillai S, Austin J, Fredette ME, Serrano-Gonzalez M. Severe Hypothyroidism and Large Goiter due to Iodine Deficiency in an Adolescent Male in the United States: A Case Report and Review of the Literature. Case Rep Endocrinol. 2022 Nov 2;2022:7235102. doi: 10.1155/2022/7235102. PMID: 36387937; PMCID: PMC9646315.

Acquired hypothyroidism refers to hypothyroidism that develops after the first year of life.   It typically occurs in childhood or adolescence.  The most common cause of acquired hypothyroidism is due to auto immunity.  It is a condition that arises when the body's immune system attacks the thyroid cells.  Autoimmune conditions can cause either a transient over-active or a transient or permanent under-active or non-functioning gland. An individual can have both an overactive and an under active phases during this autoimmune-related destructive phase.

I treated a patient with a profound case of acquired hypothyroidism several years ago.   Before endocrine consultation, her pediatrician had noticed the patient was not being growing well.  This prompted an evaluation to include thyroid function testing. The test results revealed severe hypothyroidism with undetectable endogenous thyroid hormone production (extremely elevated TSH and low ft4).

During my consultation with the family, the mother informed me that her daughter transitioned to sedentary type activities over the last several years.  She was previously more active but over the years developed a preference for reading and drawing.  Due to her severe hypothyroidism, she was placed on thyroid hormone with a with a very gradual increase in the dose to ensure tolerability.  Gradually over the next several months her thyroid function normalized on thyroid hormone replacement.  In parallel,  her linear growth picked up nicely.  She also started to have other physical changes.   Her face became less coarse appearing, puffy as her thyroid labs normalized.  Mother also noted that she became for active and now did not sit for prolonged times.

Acquired hypothyroidism is treated with thyroid hormone replacement. Thyroid hormone replacement is very important for a growing child because it is needed for muscle function, bone health and growth and development.  It does require close lab monitoring for dose adjustments.   A child will outgrow their dose over time, but dosage adjustments are strictly based on lab results and are not weight based per se.  During puberty, thyroid function tests are done more frequently as a child is more likely to outgrow their dose and need dose adjustments.