Hyperthyroidism

Hyperthyroidism is a state of high circulating thyroid hormones, arising either from overproduction from the thyroid gland or extrathyroidal, including exogenous, sources. Thyrotoxicosis refers to the clinical syndrome that results from excess thyroid hormone. Thyroid storm is the most severe form of thyrotoxicosis, resulting in the extreme alteration of usual hyperthyroid signs and symptoms. The diagnosis can occur in patients with or without preexisting hyperthyroidism. It is a rare diagnosis and usually triggered by precipitants such as trauma, myocardial infarction, surgery (including thyroid surgery for hyperthyroidism or other surgeries in general), or infection.  Thyroid storm is a medical emergency, warranting immediate administration of medications to block the production and release of thyroid hormone, and supportive management of systemic illness.
 
Causes of Hyperthyroidism

• Graves’ Disease

• Thyroid tumor/nodule

• Excessive intake of thyroid hormones

• Abnormal secretion of TSH

• Thyroiditis

• Excessive iodine intake

 
Signs and Symptoms of Hyperthyroidism

• Hot flashes, sweating

• Tachycardia

• Hypertension

• Anxiety, nervousness

• Weight loss

• Hair loss

• Difficulty sleeping, restlessness

• Tremors in the hands

• Weakness

• Diarrhea

• Emotional instability, irritability or fatigue

• Goiter

• Moist, sweaty skin

• Exophthalmos, lid lag

Treatment of Hyperthyroidism
There are two main antithyroid drugs available: methimazole and propylthiouracil. It is important to note that these medications can cause occasional suppression of white blood cell production. Medications are also available to immediately treat the symptoms caused by excessive thyroid hormones, for example, a beta-blocker to manage tachycardia. 

Radioactive iodine is another option to treat hyperthyroidism. A one-time oral treatment ablates the hyperactive gland. However, permanent hypothyroidism is the major complication of this form of treatment.
Surgical removal of the thyroid tissue that is producing the excessive thyroid hormone is another option.  A major complication is disruption of the surrounding tissue, including accidental removal of the parathyroid glands, resulting in low calcium levels and thus requiring calcium replacement.

Special Populations

Pregnancy
Thyroid dysfunction in pregnancy is associated with preeclampsia, spontaneous abortion, abnormal fetal brain development, and fetal mortality. In general, increased dosage requirements of thyroid replacement medications should be anticipated, especially during first and second trimesters.
             
Children
Thyroid hormones play a critical role in neurologic development in children. Low or absent levels of thyroid hormone may result in cretinism, and neonatal hypothyroidism accounts for the most preventable cause of intellectual disability. 
 
Elderly
Signs and symptoms of hypothyroidism may be very subtle and mistakenly attributed to normal aging changes. Taking a careful history is important to make the correct diagnosis and helps to avoid erroneous diagnoses of heart failure, dementia or depression.  

Thyroid Function Tests (TFTs)

Thyroid function tests (TFTs) are used to screen thyroid activity. TSH is the gold standard for evaluating thyroid function.

When screening for thyroid dysfunction:
     • If the TSH is normal, no further testing is required.
     • If the TSH is high, check free T4 to determine the degree of hypothyroidism.
     • If the TSH is low, check free T4 and T3 to determine the degree of hyperthyroidism. 
     • If pituitary or hypothalamic disease is suspected, check both serum TSH and free T4.
     • If TSH is normal, but patient has convincing symptoms of thyroid dysfunction, check free T4.

Note: TSH levels peak in the evening and are at their lowest in the afternoon. Also, levels may vary with severe stress, illness, trauma, and low energy intake.