Thyroid Disease

Thyroid disease frequently arises from autoimmune processes that stimulate overproduction of hormones or cause gland destruction which subsequently leads to underproduction of hormones.

Epidemiology

• Incidence
  • Hypothyroidism
    • 6-8/10,000
    • Increases with age
  • Hyperthyroidism
    • 1-2% of the population
• Age – Age of onset 40-60 years for both types
• Sex – 5-8 times more common in females for both types

Hypothyroidism

• Caused by underproduction of hormones
• Etiologies
  • Autoimmunity
  • Iatrogenic (treatment of hyperthyroidism)
  • Iodine deficiency (worldwide)
  • Drugs
• Clinical Presentation
  • Insidious onset is common
  • Fatigue, hair loss, cold intolerance, weight gain, dry coarse skin, alopecia, bradycardia, carpal tunnel syndrome, skin thickening (myxedema), constipation
  • Most serious manifestation is myxedema coma
• Diagnosis
  • Initial evaluation should include thyroid stimulating hormone (TSH) followed with Free T₄ (FT₄)
  • Hypothyroidism during pregnancy may cause fetal demise and low IQ in liveborn (endemic cretinism) infants
    • Order TSH and TPO antibody testing for patients who have a prior diagnosis of or family history of hypothyroidism
    • Elevated TPO antibodies associated with post-partum thyroiditis
• Treatment
  • Hypothyroid pregnant patients may require increase of replacement
    • Monitor with TSH and Free T₄ or T₄

Hyperthyroidism (Thyrotoxicosis)

• Caused by overproduction of thyroid hormones
• Etiologies
  • Graves disease accounts for 60-80% of cases
    • Autoimmune – thyroid stimulating immune globulins (TSI IgG) bind to thyrotropin receptors on the thyroid gland
  • Toxic multinodular or uninodular goiter
    • Secrete hormone autonomously
  • Thyroiditis
    • Postpartum
    • Subacute
  • Other – TSH secreting tumors (rare), ingestion of T₃, T₄, drug-induced (amiodarone)
• Clinical Presentation
  • Hyperactivity, heat intolerance, fatigue, weakness, diarrhea, tachycardia, tremor, goiter, weight loss
  • Diffuse nontender enlargement of the gland
  • Ophthalmopathy – occurs in 30% of patients and consists of protrusion of the eyes & periorbital swelling
• Diagnosis
  • Initial evaluation involves TSH measurement (decreased), Free T₄ (increased)
  • Further evaluation may include thyroid antibody evaluation
• Treatment usually required

Pregnancy-related thyroid disease

• Pathophysiology
  • Thyroid binding globulin levels (TBG) are elevated as estrogen increases
  • Increased TBG causes a shift in T₃ and T₄ reference ranges 1.5 times the nonpregnant state; always use trimester specific reference values
  • Reference intervals for free T₄ have not been well established in pregnant patients, and so some authors advocate use of total T₄ in place of free T₄ during pregnancy
  • TSH falls and may be below the lower adult reference limit in 20% of pregnancies
• Hypothyroidism in 0.3-0.7% of pregnancies
  • Associated with infertility, low birth weight, low fetal IQ, fetal demise, hypertension, placenta abruptio and post partum hemorrhage
  • Patient complains of low energy, inappropriate weight gain, constipation, goiter, cold intolerance and bradycardia
  • May or may not affect fetus
  • Most common cause is chronic autoimmune thyroiditis
• Hyperthyroidism in 0.2% of pregnancies
  • Associated with spontaneous abortions, infertility, still births, low birth weight, pre-term delivery, fetal or neonatal hyperthyroidism, congestive heart failure in mother
    • In 2% of pregnancies, T₄ is supranormal around 10-12 weeks because hCG is at its peak and TSH is at its nadir
  • Patient complains of weight loss, goiter, muscle weakness, palpitations, onycholysis, tachycardia and eye changes
  • Conditions causing thyroid dysfunction during pregnancy
    • Hyperemesis gravidarum,
    • Trophoblastic tumors such as choriocarcinoma
    • TSH receptor mutations
  • Gestational transient thyrotoxicosis
    • Frequently associated with hyperemesis gravidarum in first trimester

Hypopituitarism  

Osteoporosis

Thyroid Cancer  

Thyroid, Autoimmune  

Indications for Ordering

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