Thyroid Function and Disease in Adolescents and Young Adults



Thyroid Function and Disease in Adolescents and Young Adults


Cecilia A. Larson





KEY WORDS



  • Goiter


  • Graves disease


  • Hyperthyroidism


  • Hypothyroidism


  • Thyroid cancer


  • Thyroid nodules


  • TSH


The thyroid is both affected by and contributes to diverse aspects of development including physical and intellectual growth and sexual development. There are thyroid receptors throughout the body that mediate the effects of thyroid hormone that is itself regulated by pituitary thyroid-stimulating hormone (TSH), which in turn is regulated by the hypothalamic hormone thyroid-releasing hormone (TRH). Disruption of the normal process of thyroid regulation affects thyroid function, causing either underactivity (hypothyroidism) or overactivity (hyperthyroidism) of the thyroid gland. In addition to disorders of thyroid function, the adolescents and young adults (AYAs) is susceptible to structural disorders of the thyroid including thyromegaly and nodular thyroid disease. Timely detection and treatment of thyroid disease during adolescence and early adulthood is essential for normal growth and development. This chapter discusses both functional and growth disorders of the thyroid and presents an approach to detection, evaluation, and management of these disorders. The framework for recognition of thyroid disorders relies on an understanding of thyroid development, a complete medical history, physical examination, and laboratory and imaging evaluations.


THYROID MIGRATION, GROWTH, AND FUNCTION DURING DEVELOPMENT



  • The thyroid gland forms during the first trimester of fetal development from the medial and lateral anlagen and follows a complex migratory path.


  • Insufficient migration can lead to a lingual thyroid. Lingual thyroids may cause obstruction of the upper airway or develop thyroid cancer, but are not routinely removed if these complications do not develop.


  • Partial nonclosure of the migratory tract can lead to a thyroglossal duct cyst; thyroglossal duct cysts are usually benign and not of clinical significance unless infection of the cyst occurs, which may require surgical intervention.


  • Postnatally to age 8 years, thyroid growth is similar and steady in males and females.


  • During puberty, there is a more than four-fold increase in thyroid volume, which correlates not only with age and gender, but also with weight, height, body mass index, and pubertal stage.1


  • By the end of puberty, the average weight of the female thyroid is 14.4 g, and for the male, it is 16.4 g.2


  • Despite the significant increased growth of the thyroid during puberty, levels of free thyroxine (fT4) and TSH decrease from age 1 year to adulthood.


  • There is an increase in thyroid disorders of both structure and function during puberty.


FOCUSED MEDICAL HISTORY

Medical conditions and genetic syndrome that are associated with an increased risk of thyroid functional disorders:



  • Trisomy 21


  • Turner syndrome


  • Klinefelter syndrome


  • Autoimmune disorders (personal or family history)



    • Rheumatoid arthritis


    • Diabetes mellitus type 1


    • Celiac disease


    • Autoimmune polyglandular syndrome

Iodine exposure increases risk of thyroid functional disorders



  • Computerized axial tomogram (CT) scan with iodinated contrast


  • Kelp or seaweed supplements


  • Amiodarone which contains iodine

Medications that can affect thyroid function



  • Lithium


  • Valproate


  • Amiodarone


  • Interferon


  • Thionamides


  • Interleukin-2


  • Tyrosine kinase inhibitors


  • Dopamine


  • Dobutamine


  • Glucocorticoids


  • Bexarotene

Thyroid cancer risk is increased in certain syndromes and with positive family history of certain types of thyroid cancer:



  • Cowden syndrome


  • Bannayan-Riley-Ruvalcaba syndrome


  • Gardner syndrome


  • Multiple endocrine neoplasia (MEN) type 2


  • Familial medullary thyroid cancer









    TABLE 12.1 Clinical Effects of Thyroid Hormone





























































    Clinical Effect

    Hyperthyroidism

    Hypothyroidism


    Height velocity

    Increased

    Decreased


    Weight

    Decreased

    Increased


    Temperature

    Increased in extreme cases

    Decreased in extreme cases


    Hair and skin

    Oily and hair loss diffusely


    Pretibial myxedemaa

    Dry


    Myxedema generalized


    Fingernails

    Ridges

    Brittle


    Bowels

    Increased frequency

    Constipation


    Cardiac

    Increased heart rate


    Atrial fibrillation

    Decreased heart rate


    Menstruation

    Lighter flow, irregular menses

    Heavier flow, irregular menses


    Skeleton

    Bone loss


    Advanced bone age

    Normal bone density


    Delayed bone age


    Blood pressure

    Systolic hypertension


    Increased mean arterial pressure

    Diastolic hypertension


    Eyes

    Stare, lid lag, dry eye exophthalmosa

    Periorbital edema


    Reflexes

    Normal

    Delayed relaxation


    Cognition

    Decreased school performance

    Decreased school performance


    a Associated specifically with Graves Hyperthyroidism.



  • Familial papillary thyroid cancer (PTC)


  • Carney complex type 1

Ionizing radiation exposure increases risk of both functional (hypothyroidism) and structural disorders, increasing the risk of both benign nodule and cancer formation.



  • Radiation treatment for childhood cancers


  • Fallout from nuclear reactor accidents

The review of symptoms is especially relevant since thyroid hormone affects so many different tissues and organ systems. For a list of functional symptoms associated with thyroid activity, see Table 12.1

Structural symptoms such as airway or esophageal obstruction and hoarseness are less common than functional symptoms, although structural signs such as an enlarged thyroid commonly lead to thyroid evaluation.

While thyroid function and gland size and structure are sometimes related, it is important to recognize that hypo-, hyper-, and eu-thyroidism can exist in normal, small, enlarged (goitrous), or nodular thyroid glands. Thus, it is critical to assess both structure and function of the thyroid.


PHYSICAL EVALUATION OF THYROID STRUCTURE



  • Inspection, palpation, and imaging by ultrasound, CT, or magnetic resonance imaging all provide information about the physical aspects of the thyroid gland.


  • Inspection (see Fig. 12.1) and palpation are best evaluated while the patient swallows, causing the thyroid to elevate. Ultrasound of the thyroid is the preferred imagine modality to assess thyroid gland structure. It allows for quantification of the size of the gland or a lesion, so it can be monitored and compared with a subsequent ultrasound. In addition, it can also identify features that aid in clarifying the diagnosis of thyroid enlargement:



    • Autoimmune thyroiditis



      • Diffuse heterogeneity is present.


    • Nodule(s)



      • Low risk for cancer:



        • Hyperechoic


        • Peripheral vascularity


        • Spongiform appearance


        • Resembles puff or Napoleon Pastry


        • Comet-tail shadowing


      • Increased risk for cancer:



        • Hypoechoic


        • Microcalcifications


        • Central vascularity


        • Irregular margins


        • Incomplete halo


        • Nodule is taller than wide


        • Significant growth of nodule


LABORATORY EVALUATION OF THYROID FUNCTION

Thyroid function is typically assessed by measuring blood tests associated with thyroid activity, and can aid in determining whether the signs and symptoms that the individual displays are indeed related to thyroid status. The most useful test is TSH, followed by fT4. In selected situations, total triiodothyronine (T3), reverse T3 (rT3), and thyroid antibody testing is necessary and helpful in establishing a diagnosis and/or monitoring response to therapy.



  • TSH is the most sensitive assay of thyroid function in steady-state situations.


  • When TSH is abnormal, or if a central (hypothalamic or pituitary) abnormality is suspected, fT4 is also measured.


  • Total T3 is helpful when TSH is suppressed to identify and monitor response to antithyroid treatment in Graves disease.


  • In inflammatory thyrotoxicosis due to release of preformed thyroid hormone, the ratio of T4:T3 is preserved (4:1).


  • When acute illness is a factor, rT3 levels can be measured, which if elevated suggests that the changes observed in TSH, early suppression followed by elevation, are associated with the acute illness and recovery phases. A “sick-euthyroid” pattern may also be reflected by a low total T3, a pattern common in AYAs with eating disorders.


  • The most specific thyroid antibody is thyroid-stimulating antibody (TSAb), which is typically measured in hyperthyroid patients to confirm Graves disease.


  • Thyroid peroxidase (TPO) antibody is the most sensitive antibody to detect autoimmune thyroid disease and can be elevated in patients with either hypo- or hyperthyroidism. It is most helpful in subclinical hypothyroidism where fT4 is normal and there is a mild TSH elevation <10 mU/L, where the presence of elevated TPO antibodies is associated with higher risk for overt hypothyroidism and can be an indication for thyroid hormone treatment.


RADIOLOGIC EVALUATION OF THYROID FUNCTION

The nuclear medicine thyroid scans allow the use of a small dose of a radioactive tracer whose thyroid and whole-body uptake can be imaged and quantified. There are three main uses of nuclear medicine studies for thyroid disorders:

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Sep 7, 2016 | Posted by in ONCOLOGY | Comments Off on Thyroid Function and Disease in Adolescents and Young Adults

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