“Our body always strives for balance and the endocrine system is an essential piece of how that happens."

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Quick Endocrine Review

The Endocrine System is composed of nine glands that produce and respond to hormones in the body to maintain homeostasis. Our body always strives for balance and the endocrine system is an essential piece of how that happens. The glands of the endocrine system include the hypothalamus, pituitary, pineal, thyroid, pancreas, adrenal, testes, and ovaries. Most of the hormones regulated by these glands are regulated through feedback loops. Endocrine disorders aren't super common in neonates but lets review a few of them.

Hypothyroidism

The thyroid has many important functions: regulating body temperature, influencing metabolism, cell growth and cellular differentiation. Thyroid hormones are released as a part of the hypothalamus-pituitary-thyroid axis. Low concentrations of thyroid hormones (T3 & T4) stimulated the release of thyroid-releasing hormone (TRH) by the hypothalamus. The TRH binds to receptor cells in the anterior pituitary gland which causes the release of thyroid stimulating hormone (TSH). TSH binds to receptor cells in the thyroid stimulating the synthesis and release of thyroid hormones (T3 and T4). When there are adequate amounts of circulating T3 and T4 the negative feedback loop tells the hypothalamus to stop producing TRH.

Congenital hypothyroidism is the most common endocrine disorder that presents in the neonatal period. When congenital hypothyroidism goes undetected and untreated the infant is at risk of intellectual disability. Congenital hypothyroidism occurs due to thyroid dysgenesis (incomplete development of the thyroid), thyroid dyshormonogenesis (inadequate thyroid hormone production), or central hypothyroidism (deficiency or irregularity in the hypothalamus or pituitary gland).

Congenital hypothyroidism affects nearly every bodily system. Clinical signs include hypothermia, bradycardia, edema, prolonged jaundice, lethargy, poor feeding, constipation, and a hoarse cry. Infants may have a goiter, large posterior fontanelle, umbilical hernia, macroglossia, and hypotonia. Diagnostic evaluation may be initiated due to a positive result on a state newborn screen. However, false positives can occur if the screen is collected in the first 24 hours of life due to the physiologic spike in TSH after birth.

Confirmatory testing of primary hypothyroidism would reveal high TSH and low T4 levels. In the rare case of central hypothyroidism, TSH would be normal or low and free T4 would be low. Treatment is aimed at normalizing T4 levels with thyroid hormone replacement therapy (Levothyroxine). Levothyroxine should be administered 1/2 hour prior to a feeding and not with medications known to affect absorption (e.g. iron, calcium). Tablets are crushed and mixed with breastmilk, formula, or water. They cannot be mixed with soy based formulas.

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Congenital Adrenal Hyperplasia

The adrenal glands are an extremely important organ that produces hormones to help regulate metabolism, the immune system, blood pressure, the response to stress, and synthesis of sex hormones. The adrenal gland produces glucocorticoids (cortisol) and mineralcorticoids (aldosterone). This is partially done through the Hypothalamic-Pituitary-Adrenal (HPA) axis.

Let's review the HPA axis real quick: In response to stress the hypothalamus releases corticotropin releasing hormone (CRH) and arginine (vasopressin). CRH travels to the anterior pituitary gland where it stimulates the release of adrenocorticotropic hormone (ACTH). ACTH travels to the adrenal cortex where it stimulates the release of cortisol. When the levels of cortisol are in the upper limit of normal, this sends a negative feedback loop to the hypothalamus to stop producing CRH.

Cortisol is an important stress hormone which drives glucose homeostasis, protein catabolism, peripheral insulin resistance, fat deposition, and maintaining cardiac output. Aldosterone is essential to maintaining euvolemia and adequate blood pressure by increasing sodium reabsoption, potassium excretion, and water retention. Aldosterone is regulated by the renin-angiotensin system and K+ concentrations.

Congenital Adrenal Hyperplasia (CAH) is an autosomal recessive disorder that disrupts the production of cortisol and aldosterone due to an enzyme deficiency.

The most common enzyme deficiency causing CAH is 21-hydroxylase (OHD) deficiency. 21-OHD is an enzyme required to synthesize cortisol. When there is 21-OHD deficiency progesterone cannot be converted into cortisol and aldosterone. The absence of cortisol stimulates and overproduction of ACTH, causing overgrowth (hyperplasia) of the adrenal gland. In addition, the precursor to cortisol (17-OHD) accumulates since its conversion to cortisol is blocked. This causes an overproduction of androgens which causes virilization is genetically female newborns. In addition, the lack of cortisol and aldosterone causes the infant to become hypoglycemic, go into a salt wasting state, lose intravascular volume, become hypotensive, and eventually go into shock.

The physiology of CAH is interesting (and a little confusing) and you are probably wondering "what will I actually see when caring for a baby with CAH?". There are two forms: "Classic" and "Non-Classic". The non-classic form may not present until puberty with hirsutism and menstrual irregularity in young women, or there may be no symptoms so we would see the Classic form of CAH in the NICU.

In the classic form genetically female infants are often identified to have CAH at birth due to their abnormal genitalia. CAH is the most common cause of ambiguous genitalia in the neonate (good to know if your studying for your certification exam). Findings may include clitoromegaly and posterior fusion of the labia majora with rugae. In very severe cases, these babies can be mistaken for genetically male newborns due to the clitoral hypertrophy that is so marked that it resembles a penile urethra. The ambiguous genitalia in females can be life saving as it helps identify CAH and ensure treatment is initiated.

Male infants may not be identified as quickly at birth as they will appear phenotypically male. When CAH is not identified early, newborns can present with symptoms of adrenal collapse (vomiting, weight loss, lethargy, dehydration, hyponatremia, hyperkalemia, hypoglycemia, hypovolemia, and shock) typically around 7-14 days of life.

CAH can be diagnosed by newborn screening before the salt losing state. However, false positives can occur on the newborn screen in premature and acutely ill infants or when the lab is drawn prior to 24-48 hours of life. Confirmatory diagnostic findings include an elevated 17-OHD. Cortisol and ACTH levels may assist with diagnosis and serum electrolytes should be closely monitored.

Treatment is provided by administering glucocorticoids and mineralcorticoids to restore physiologic levels of cortisol and suppress ACTH and androgen overproduction. Infants in an adrenal crisis require volume resuscitation and correction of electrolyte imbalance. Children with CAH require lifelong hormone replacement therapy and follow up.

NICU nurses are essential to helping families cope with this scary diagnosis. We must teach families how to administer lifelong steroid therapies. Stress dosing must also be reviewed in cases when the infant becomes acutely ill. Parent must learn how to provide stress dosing and IM injections in case the infant is acutely ill or unable to take medication by mouth.

Check out this great video on stress dosing by CHOP

Adrenal Insufficiency

Premature neonates have limited ability to maintain cortisol homeostasis due to adrenal insufficiency. The preterm neonates has an immature HPA axis and an inadequate pituitary response to CRH which results in low cortisol production. As with many organs, the adrenal gland is not functionally mature when a newborn is delivered preterm and therefore does not respond to stress as a mature term adrenal gland would.

Common signs of adrenal insufficiency include hypoglycemia, poor perfusion, and hypotension refractory to volume replacement and inotrope therapy. Diagnosis of adrenal insufficiency can be challenging due to the non-specific signs. Random cortisol levels can be collected, however no specific cortisol threshold is widely accepted as diagnostic. ACTH stimulation testing may be performed to assess the adrenal glands response to synthetic ACTH.

NICU nurses are critical to an accurate ACTH stimulation test. The test involves drawing a cortisol level, administering a synthetic ACTH, then drawing another cortisol level exactly 30 minutes after the ACTH administration.

Treatment of adrenal insufficiency involves administration of hydrocortisone.

What other endocrine disorders have you seen in the NICU? Email me and let me know what other topics you'd love to see in my newsletter or my instagram! 😊

Wishing you all the best!

Amanda xoxo

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References:

Brady J, Cannupp A, Myers J, Jnah AJ. Congenital Hypothyroidism. Neonatal Netw. 2021;40(6):377-385. doi:10.1891/11-T-699

Allis K. A Broken Pathway: Understanding Congenital Adrenal Hyperplasia in the Newborn. Neonatal Netw. 2021;40(5):286-294. doi:10.1891/11-T-694

Verklan, et al., Core Curriculum for Neonatal Intensive Care Nursing, Elsevier, 2021

Merke (2022). Treatment of classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency in infants and children. Retrieved from uptodate.com

Holmstrom LE, Jnah AJ. Relative Adrenal Insufficiency: Crisis Averted?. Neonatal Netw. 2021;40(6):369-376. doi:10.1891/11-T-703

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