Hypothyroidism 甲状腺功能减退

Hypothyroidism is a condition that comes from your thyroid gland producing inadequate amounts of thyroid hormones in the bloodstream. Common symptoms of hypothyroidism include fatigue, sensitivity to cold, constipation, dry skin, weight gain, puffy face, hoarseness, muscle weakness, elevated cholesterol, muscle aches, tenderness, stiffness, joint pain, swelling, irregular or heavy menstrual periods in women, thinning hair, depression, impaired memory, and slowed heart rate (Mayo Clinic, 2018).

Clinical manifestations:

• Fatigue and lethargy
• Weight gain
• Complaints of cold hands and feet
• Temperature and pulse become subnormal; patient cannot tolerate cold and desires increased room temperature
• Reduced attention span; impaired short-term memory
• Severe constipation
• Generalized appearance of thick, puffy skin; subcutaneous swelling in hands, feet, and eyelids
• Thinning hair, loss of the lateral one-third of eyebrow
• Menorrhagia or amenorrhea
• Neurologic signs include polyneuropathy, cerebellar ataxia, muscle aches or weakness, clumsiness, prolonged deep tendon reflexes
• Hyperlipoproteinemia and hypercholesterolemia
• Enlarged heart on chest x-ray
• Increased susceptibility to all hypnotic and sedative drugs and anesthetic agents
• Syndrome of subclinical hypothyroidism: state in which the patient is asymptomatic and the free T4 level is within the normal range; however, the TSH level is elevated, suggesting impending thyroid gland failure. Therefore, many clinicians may elect to treat this condition as if the patient were symptomatic.

Hypothyroidism is the most common endocrine disease in the United States. In the general population, the prevalence is 3.8-4.6%. The incidence of hypothyroidism is almost seven to ten times higher worldwide in women than men:  4.2/1000 in women and 0.6/1000 in men and in the UK, as woman over the age of sixty are at highest risk of needing replacement medication to treat a deficiency of thyroid hormone. In addition, studies conclude that the incidence of this disease is rising (Chakera, A., et al, 2012).

Older adults have an increased risk of developing hypothyroidism. However, many of the symptoms of hypothyroidism are not recognized as such in this age group, or they may be asymptomatic (American Thyroid Association, n.d.). In this age group thyroid function tests should be run if there are even slight indications of thyroid disease or if there is a family history. It should be noted that there is a correlation in older adults with subclinical hypothyroidism of increased risk of atherosclerosis, myocardial infarction, and heart failure (Kostoglou-Athanassiou & Ntalles, 2010).

Primary hypothyroidism is the most common form of hypothyroidism; it is when there is a destruction of normal thyroid tissue by genetic factors or environmental factors such as smoking, obesity or pregnancy. Central and secondary hypothyroidism is another type of hypothyroidism which is rare and starts at the level of the pituitary and results in the decrease secretion of thyroid-stimulating hormone (TSH). The last kind of hypothyroidism is sub-clinical, mild or tertiary hypothyroidism that occurs only in adults and is the reduced Thyrotropin hormone (TRH) which is not being released from the hypothalamus which reduces TSH (Braun, 2017):

• Primary hypothyroidism is considered an autoimmune disease in 50% od patients. The causative factors are:
  • The immune system produces antibodies that attack the thyroid gland causing autoimmune thyroiditis and thus the inability to produce hormones.
  • Thyroid hormones (T3 and T4) are diminished and unable to function.
  • Low levels of circulating T3, T4 cause an increase of TSH from the pituitary.
• Additional exogenous etiology includes:
  • Partial or complete thyroidectomy
  • Treatment for hyperthyroidism
  • Previous radiation to the head or neck
  • Medications such as lithium or amiodarone
• Secondary hypothyroidism claims the following causes:
  • Pituitary disorder, such as benign pituitary adenoma
  • Causes failure to produce adequate TSH
  • Iodine deficiency, needed to produce thyroid hormones
  • Pregnancy ~ may also be considered autoimmune

(The Mayo Clinic, 1012)

Diagnostic evaluation:

1. Low T3 and T4 level
2. Elevated TSH levels in primary hypothyroidism (Serum TSH help determine whether the disorder is primary or secondary)
   • Increased serum TSH is due to Thyroid Insufficiency
   • Decreased or normal is due to hypothalamic or pituitary insufficiency
3. Elevation of serum cholesterol
4. Electrocardiogram- sinus bradycardia, low voltage of QRS complexes, and flat or inverted T waves
5. Elevation of thyroid peroxidase antibodies (TPO Ab) and antithyroglobulin antibodies

The standard of treatment for hypothyroidism is a medication called Levothyroxine (LT4) or also known as Synthroid. Levothyroxine is a synthetic thyroid replacement and is very effective in replacing the low levels of TSH in the blood stream. It is easy to use, affordable and has very little side effects making it the continued standard. However, TSH levels are monitored to ensure proper dosing. Adverse effects caused by levothyroxine are typically due to overdosing and may include cardiac dysrhythmias, insomnia, headache, tremor, anxiety, nausea, diarrhea, cramps, weight loss, sweating, heat intolerance, fever, and menstrual irregularities (Lilley, Rainforth-Collins, & Snyder, 2017).

References:

American Thyroid Association. (n.d.). Older patients and thyroid disease. Retrieved from https://www.thyroid.org/thyroid-disease-older-patient/

Braun, C. A., & Anderson, C. M. (2017) Applied pathophysiology: A conceptual approach to the mechanisms of disease (3^rd. ed)

Chakera, A.J., Pearce, S., Vaidya, B., (2012) Treatment for primary hypothyroidism: current approaches and future possibilities. Drug Des Devel Ther. 2012; 6: 1-11.

Kostoglou-Athanassiou, I., & Ntalles, K. (2010). Hypothyroidism – new aspects of an old disease. Hippokratia, 14(2), 82–87.

Lilley, L. L., Collins, S. R., & Snyder, J. S. (2017) Pharmacology and the nursing process (8^th ed.). Canada:Elsevier

Mayo Clinic. (2018). Hypothyroidism (underactive thyroid). Retrieved from https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284

The Mayo Clinic, 2012. Hypothyroidism.