Thyroid Dysfunction: Thyroid Glands Disorders
• Approximately 20 million Americans are afflicted with thyroid disease.
• 60% of the population with thyroid disorders are believed to be unaware of their abnormality.
• Women are five to eight times more likely than men to have a thyroid problem.
• Palpable thyroid nodules are found in 5% to 7% of the North American population.
• Thyroid imaging studies (radioisotope scans or ultrasounds) increase the number of nodules found in an individual and in a population. However, thyroid cancers are rare (<5% of thyroid nodules) and deaths from thyroid cancer are also very uncommon.
• Hypothyroidism (clinical and subclinical) is 10 times more prevalent than hyperthyroidism (clinical or subclinical).
• Screening for a thyroid disorder with a TSH value is controversial.
• Most thyroid diseases require lifelong follow-up and medical management.
• Thyroxine (T4) is the principal product of the thyroid gland. However, T4 is sometimes considered a prohormone because it must be converted to triiodothyronine (T3) to exert its biological effects.
• T4 is highly protein bound, for example, 99.96% is bound to thyroxine-binding globulin (TBG), albumin, transthyretin, and lipoproteins.
• Half-life of T4 is 7 days.
• T3 is also highly protein bound (99.3%).
• Half-life of T3 is 24 hours.
• TSH controls the secretion of T4 and T3 from the thyroid gland. TSH is a glycoprotein hormone with two subunits, A (common to follicle-stimulating hormone [FSH], luteinizing hormone [LH], and human chorionic gonadotropin [HCG]) and B (unique to TSH). The half-life of TSH is 50 minutes, and its secretion is facilitated by thyrotropin-releasing hormone (TRH) secreted from the hypothalamus.
• Primary factor inhibiting TSH synthesis and secretion is T3.
Prevalence of Thyroid Dysfunction
• Hypothyroidism is present in 2% of the adult population.
• Subclinical hypothyroidism likely accounts for an additional 5% to 17%.
• Hyperthyroidism is present in <0.2% of the adult population.
• Subclinical hyperthyroidism likely accounts for an additional 0.1% to 6.0%.
Risk of Developing Thyroid Dysfunction
• Previous thyroid dysfunction
• Surgery or radiotherapy involving the gland or neck
• Diabetes mellitus, type 1
• Pernicious anemia
• Medications (lithium, amiodarone, interferon)
• Family history of thyroid disease, pernicious anemia, type 1 diabetes mellitus, or primary adrenal insufficiency
Abnormal Laboratory Tests that Accompany Hypothyroidism
• Increased creatine phosphokinase (CPK)
• Increased lactic dehydrogenase (LD)
Abnormal Laboratory Tests that Accompany Hyperthyroidism
• Increased alkaline phosphatase
• Hepatocellular enzyme elevation
• Abnormal electrocardiogram (ECG) (atrial fibrillation, atrial flutter, or supraventricular tachycardia [SVT])
• Low cholesterol
• Increased ferritin
• Increased angiotensin-converting enzyme