You found a newborn having low total thyroxine (T4) level on newborn screening. The level was drawn 24 hours after a term, healthy female neonate was born. Pregnancy was uncomplicated, and there was no maternal history of thyroid disease. Repeat testing in your office at 7 days after birth shows a thyroid-stimulating hormone level of 200 mIU/L and a low free thyroxine (FT4) level of 0.2 ng/dL (2.57 pmol/L) in this otherwise healthy girl. Her weight is 3 kg. Findings on physical examination are unremarkable.
Of the following, the BEST next step in the management of this patient is to
A. Begin treatment with levothyroxine (LT4)
B. Begin treatment with liothyronine (LT3)
C. Measure serum thyroglobulin level
D. Order a thyroid radionuclide uptake and scan
E. Order thyroid ultrasonography
ANSWER: WEDNESDAY 28/11/2018 AT 10 AM.
The infant described in this vignette has had 2 abnormal thyroid function test results indicating profound hypothyroidism. Therefore, treatment should be initiated with levothyroxine (LT4) immediately. In clear cases of congenital hypothyroidism (CH), treatment should never be delayed to obtain another study, such as a thyroid uptake scan or ultrasonography. These studies can be performed after treatment is initiated.
ReplyDeleteThe best developmental outcomes occur with levothyroxine therapy started by 2 weeks of age at 10 μg/kg or more per day, compared with lower doses or later start of therapy. There are only minor differences in intelligence, school achievement, and neuropsychological test results in adults with CH that was treated early with levothyroxine compared with control groups of classmates and siblings. However, even with early treatment impaired visuospatial processing, selective memory and sensorimotor defects can occur.
In contrast, the prognosis for normal mental and neurologic performance is less certain for infants with CH that is not detected early by newborn screening or treated later on. If treatment is delayed even a few months, 77% of infants show some signs of developmental delay and may have impairment of arithmetic ability, speech, or fine motor coordination in later life.
Knowledge of the normal range for thyroid function tests in the first year of life is important in deciding whom to treat and how soon treatment is needed to prevent adverse developmental outcomes. Shortly after birth, there is a cold-stimulated surge of thyrotropin (TSH) in the infant that peaks by 30 minutes of life. TSH levels then gradually decrease, so that by 24 hours the TSH level is typically less than 20 to 25 mIU/L. If the TSH level is greater than 25 mIU/L at 24 hours of life, a confirmatory test should be performed. Confirmatory serum testing should be performed in infants before 2 weeks of age, when the upper TSH range has decreased to approximately 10 mIU/L. For persistent elevation of TSH (as seen in the infant in this vignette), treatment should be started with levothyroxine immediately at 10 to 15 pg/kg per day. There is no current recommendation for using liothyronine (LT3) in the routine care of infants with congenital hypothyroidism.
The treatment of infants with TSH elevations between 5 and 10 mIU/L that persist after the first month of life is controversial. A TSH range of 1.7 to 9.1 mIU/L has been reported for children 2 to 20 weeks of age. Other studies report that repeated episodes of TSH levels greater than 5 mIU/L after the age of 6 months were the most important variables associated with developmental delay. Thus, if treatment is begun for a mild elevation of TSH between 5 and 10 mIU/L in the first year of life, consideration should be given to an underlying transient cause, and a trial off therapy at 3 years of age should be considered.
Measurement of serum thyroglobulin (TBG) can be performed if confirmatory testing reveals a normal free thyroxine (FT4) level when the initial total thyroxine (T4) level on screening was low. TBG deficiency can lead to a low total T4 measurement due to a decreased amount of thyroid hormone bound to TBG, but this is not clinically relevant because the FT4 will be normal.
CORRECT OPTION IS ‘A’
Great and thank you sir
ReplyDeleteGreeeeettttttt
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