Thyroid Disorders: Hypothyroidism and Hyperthyroidism

The thyroid gland regulates metabolism, heart rate, body temperature, and energy. When it produces too little hormone (hypothyroidism) or too much (hyperthyroidism), nearly every body system is affected. This note compares the two conditions and reviews the key labs, medications, and nursing priorities tested on the NCLEX.

Overview

• The thyroid gland is a butterfly-shaped endocrine gland in the front of the neck.
• It produces thyroid hormones (T3 and T4) that regulate metabolism, heart rate, temperature, and energy.
• Disorders arise when hormone production is insufficient (hypothyroidism) or excessive (hyperthyroidism).

Quick Comparison

Hypothyroidism

What it is

• The thyroid produces insufficient hormone, so body systems slow down.
• Hashimoto's thyroiditis is the most common cause.
• Other causes: iodine deficiency, thyroidectomy, and medications such as lithium and amiodarone.

Signs and symptoms

• Fatigue and lethargy affecting daily activities.
• Cold intolerance from slowed metabolism.
• Weight gain despite poor appetite.
• Bradycardia and hypotension.
• Constipation from decreased GI motility.
• Dry, coarse skin and brittle hair.
• Myxedema: non-pitting edema around eyes, hands, and feet.
• Deep tendon reflexes with delayed relaxation.
• Depression and memory impairment.
• Menorrhagia (heavy menstrual bleeding) in women.

Life-threatening complication

• Myxedema coma — severe hypothyroidism with hypothermia, hypotension, and altered mental status.

Hyperthyroidism

What it is

• The thyroid produces excessive hormone, so body systems speed up.
• Graves' disease is the most common cause.
• Other causes: toxic multinodular goiter, thyroiditis, excessive thyroid hormone replacement, or iodine excess.

Signs and symptoms

• Nervousness, anxiety, and irritability are early signs.
• Heat intolerance and excessive sweating.
• Weight loss despite increased appetite.
• Tachycardia, palpitations, and atrial fibrillation.
• Diarrhea from increased GI motility.
• Warm, moist, smooth skin.
• Fine tremor of the hands.
• Hyperreflexia with brisk deep tendon reflexes.
• Exophthalmos (bulging eyes) — specific to Graves' disease.
• Goiter (enlarged thyroid) may be visible.
• Oligomenorrhea (light menses) in women.

Life-threatening complication

• Thyroid storm — severe hyperthyroidism with high fever, extreme tachycardia, and altered mental status.

Laboratory Tests

• High TSH with low T4 → primary hypothyroidism (thyroid gland failure).
• Low TSH with high T4 → primary hyperthyroidism (overactive thyroid).

Treatment

Hypothyroidism — Levothyroxine

• Levothyroxine is the first-line drug and is taken lifelong.
• Take on an empty stomach 30–60 minutes before breakfast, with water only.
• Calcium, iron, magnesium, and antacids decrease absorption — separate by at least 4 hours.
• Signs of overdose: tachycardia, palpitations, chest pain, insomnia.
• Monitor TSH regularly to guide dosing.

Hyperthyroidism Medications

Nursing Priorities

• Hypothyroidism: monitor weight, heart rate, and bowel movements; provide a warm environment and a high-fiber diet; watch for myxedema coma; ensure levothyroxine adherence.
• Hyperthyroidism: monitor weight, heart rate, and temperature; provide a cool environment and frequent small meals; watch for thyroid storm and atrial fibrillation; teach patients on methimazole/PTU to report fever or sore throat.

Patient Teaching

• Take levothyroxine on an empty stomach; separate from calcium and iron by 4 hours.
• Never stop thyroid medications abruptly.
• Report fever or sore throat immediately if taking methimazole or PTU.
• Wear medical alert identification.
• Hypothyroidism: stay warm, eat high-fiber foods.
• Hyperthyroidism: stay cool, avoid stimulants such as caffeine.
• Seek emergency help for signs of myxedema coma (hypothermia, confusion) or thyroid storm (high fever, severe tachycardia).

Key takeaways

• Hypothyroidism slows everything down (bradycardia, weight gain, cold intolerance); hyperthyroidism speeds everything up (tachycardia, weight loss, heat intolerance).
• Labs: high TSH + low T4 = hypothyroidism; low TSH + high T4 = hyperthyroidism.
• Levothyroxine is lifelong, taken on an empty stomach, and separated from calcium/iron by 4 hours.
• Methimazole and PTU require monitoring — report fever or sore throat (agranulocytosis); PTU also carries a hepatotoxicity warning.
• Recognize the emergencies: myxedema coma in hypothyroidism and thyroid storm in hyperthyroidism.
• PTU is the preferred antithyroid drug in pregnancy and thyroid storm.