Hyperthyroidism refers to a group of disorders characterized by increased thyroid hormone levels in circulation, leading to widespread hypermetabolism in the body. It can be classified into three categories: primary hyperthyroidism, secondary hyperthyroidism, and hyperfunctioning adenoma.
Primary Hyperthyroidism
This is the most common form, and it involves thyroid enlargement accompanied by symptoms of hyperthyroidism. Patients are typically between 20 and 40 years old. The thyroid gland exhibits diffuse and symmetrical enlargement affecting both lobes. It is often accompanied by eye bulging, which is why it is also referred to as "exophthalmic goiter."
Secondary Hyperthyroidism
Secondary hyperthyroidism is less common and may occur in conditions such as nodular goiter. Patients often have a history of nodular goiter lasting many years before hyperthyroid symptoms appear. This condition typically affects individuals older than 40 years of age, with gland enlargement showing nodular characteristics and asymmetry. Eye bulging is absent, but there is a higher risk of cardiac damage.
Hyperfunctioning Adenoma
Hyperfunctioning adenoma is rare and involves the presence of one or more autonomous, hyperfunctioning nodules within the thyroid gland. Eye bulging is absent, and the surrounding thyroid tissue remains normal or displays atrophic changes.
Etiology
The exact causes of hyperthyroidism remain unclear. Primary hyperthyroidism is often thought to be an autoimmune disorder, while secondary hyperthyroidism and hyperfunctioning adenoma are likely related to secretion disorders within the thyroid nodules themselves.
Clinical Manifestations
Symptoms of hyperthyroidism include thyroid gland enlargement, irritability, excitability, insomnia, hand tremors, heat intolerance, excessive sweating, moist skin, increased appetite with weight loss, heart palpitations, a rapid and strong pulse (often exceeding 100 beats per minute, even during rest or sleep), widened pulse pressure (mainly due to elevated systolic pressure), endocrine abnormalities such as menstrual irregularities, and general fatigue or weakness. Increased pulse rate and widened pulse pressure are particularly important indicators for assessing disease severity and treatment effectiveness.
Diagnosis
Diagnosis primarily relies on clinical manifestations, supplemented by auxiliary tests. Common auxiliary diagnostic methods include:
Serum TSH, T3, and T4 Measurements
TSH serves as the first-line screening marker for hyperthyroidism due to its high specificity. In early stages of hyperthyroidism, T3 levels tend to rise earlier and more rapidly than T4 levels, rendering T4 measurements less significant for early detection. Free T3 (FT3) and free T4 (FT4) are unaffected by thyroid hormone-binding proteins and directly reflect the functional status of the thyroid gland; these are central indicators for clinical diagnosis.
Thyroid 131I Uptake Rates
Normal thyroid glands absorb 30–40% of the total iodine-131 dose within 24 hours. Hyperthyroidism can be diagnosed if the thyroid absorbs more than 25% of the iodine dose within 2 hours or exceeds 50% uptake within 24 hours, especially if the peak uptake occurs earlier than usual.
Basal Metabolic Rate Measurements
The basal metabolic rate (BMR) can be estimated based on pulse rate and pulse pressure or measured using specialized equipment, with the latter offering greater reliability. Measurements must be conducted while the patient is fasting and fully at rest. The formula commonly used for calculation is:
BMR = (Pulse Rate + Pulse Pressure) - 111.
A normal BMR falls within the range of ±10%. Hyperthyroidism is graded as mild (BMR of +20% to +30%), moderate (+30% to +60%), or severe (+60% and above).
Surgical Treatment
Surgery is one of the main treatment methods for hyperthyroidism. It provides a rapid and effective resolution but is associated with a certain risk of surgical complications, making it critical to carefully consider both surgical indications and contraindications.
Indications for Surgery
Indications include:
- Secondary hyperthyroidism or hyperfunctioning adenoma.
- Moderate or severe primary hyperthyroidism.
- Hyperthyroidism with significant thyroid enlargement causing compression symptoms, such as substernal goiter.
- Recurrence after antithyroid drug therapy or radioactive iodine therapy, or cases where long-term medication adherence is difficult.
- Suspected or confirmed thyroid malignancy.
Absolute contraindications include elderly patients or those with severe organic diseases who cannot tolerate surgery. Relative contraindications include early or late stages of pregnancy.
Surgical Techniques
Currently, available surgical methods include bilateral subtotal thyroidectomy, bilateral near-total thyroidectomy, or total thyroidectomy. Bilateral near-total or total thyroidectomy is effective in eliminating the risk of persistent or recurrent hyperthyroidism and is the recommended surgical option for primary hyperthyroidism. These procedures should be performed by experienced surgeons to ensure protection of the recurrent laryngeal nerve and parathyroid glands during the operation.
Preoperative Preparation
Adequate and thorough preparation is necessary before surgery to minimize the risks associated with performing surgery in the context of high basal metabolic rates. This preparation reduces the likelihood of complications during and after the procedure.
General Preparation
For patients experiencing excessive anxiety or insomnia, mild sedatives or sleeping medications may be administered to alleviate their fears. For those with tachycardia, oral propranolol may be used. Patients with heart failure may receive digitalis preparations.
Preoperative Tests
In addition to a comprehensive physical examination and necessary biochemical tests, the following should be included:
- Neck X-ray or CT scan to assess the presence of tracheal compression or displacement.
- Electrocardiogram (ECG) and echocardiography to evaluate for arrhythmias or heart failure.
- Laryngoscopy to confirm vocal cord function.
- Basal metabolic rate (BMR) assessment to determine the severity of hyperthyroidism and select the appropriate timing for surgery.
Medication Preparation
This is a key component of preoperative preparation.
All hyperthyroid patients are required to use antithyroid medications before surgery (except for those who are allergic or intolerant). Surgery is performed after symptoms of hyperthyroidism are brought under control, followed by a two-week course of iodine preparations. Iodine preparations are mainly appropriate for primary hyperthyroidism and are not routinely recommended for secondary hyperthyroidism or hyperfunctioning adenoma. Since antithyroid drugs can cause thyroid gland enlargement and arterial congestion, surgery may carry a higher risk of bleeding. Administering iodine preparations for two weeks after antithyroid drug therapy helps reduce gland size, stiffen the gland, and diminish arterial congestion, making surgery safer. The preparation process is reliable but takes longer.
Commonly used iodine preparations include Lugol's solution (a compound potassium iodide solution containing 8 mg of iodine per drop). This can be administered three times daily, starting at three drops per dose and increasing by one drop per day up to 16 drops per dose. This dosage is maintained for two weeks. However, since iodine preparations only suppress thyroid hormone release and do not inhibit hormone synthesis, discontinuing iodine therapy may lead to a rebound in symptoms or even exacerbation due to decomposition of stored thyroglobulin in thyroid follicles. As such, iodine preparations are not recommended for patients who will not undergo surgery.
Antithyroid drug alone is suitable for patients with secondary hyperthyroidism or hyperfunctioning adenoma. Surgery is performed only after thyroid function is normalized through preoperative antithyroid drug treatment.
Beta-blockers are applicable for patients with contraindications for iodine preparations, those allergic to antithyroid drugs, or patients with normal thyroid function but tachycardia without contraindications. Beta-blockers, if used, are gradually tapered postoperatively. Atropine is generally avoided prior to surgery to prevent tachycardia.
Surgical and Postoperative Considerations
Anesthesia
Endotracheal intubation with general anesthesia is commonly used.
Surgical Procedure
The operation should be performed gently and meticulously. Hemostasis must be carefully achieved. Special attention should be paid to the protection of the parathyroid glands and the recurrent laryngeal nerve.
Postoperative Monitoring and Care
On the first day after surgery, close monitoring of the patient's respiratory function, temperature, pulse, and blood pressure is essential. Signs of a thyroid storm, such as rapid pulse and elevated temperature, warrant immediate attention. Patients are placed in a semi-recumbent position to facilitate breathing and drainage of blood from the surgical site. Assistance is provided to clear sputum and maintain airway patency.
For patients who undergo bilateral subtotal thyroidectomy, postoperative use of Lugol's solution is recommended. This involves administering the solution three times daily, 10 drops per dose, for approximately one week. Alternatively, Lugol's solution may begin at 16 drops per dose, tapering by one drop per day until discontinuation within 7–10 days.
Major Surgical Complications
Postoperative Respiratory Difficulty and Asphyxia
This is the most severe postoperative complication and generally occurs within 48 hours after surgery. Without timely detection and management, it can be life-threatening. Common causes include:
- Hemorrhage and hematoma compressing the trachea, which typically occur within 24 hours postoperatively.
- Laryngeal edema, mainly caused by surgical trauma but can also result from endotracheal intubation.
- Tracheal collapse, as a result of prolonged compression by the enlarged thyroid, leading to tracheomalacia. Once the thyroid gland is removed, the softened tracheal wall loses support.
- Bilateral recurrent laryngeal nerve injury.
Recurrent Laryngeal Nerve Injury
Most cases result from surgical trauma, including accidental clamping, traction, severance, or ligation of the nerve. A smaller proportion arises from hematoma compression or scarring. This complication can be classified as temporary or permanent.
Temporary injuries often result from nerve bruising, traction, or hematoma compression and usually recover within 3–6 months with timely treatment such as physiotherapy.
Permanent injuries are typically due to severance or ligation of the nerve. Nerve damage from cutting or ligation often causes symptoms immediately during or after surgery, while injuries from scarring may only manifest a few days later.
Unilateral recurrent laryngeal nerve injury typically causes hoarseness. Bilateral nerve injury can result in loss of voice or significant respiratory difficulties, potentially leading to asphyxia. Tracheotomy may be required in severe cases. Intraoperative nerve monitoring can help reduce the likelihood of recurrent laryngeal nerve injury during surgery.
Superior Laryngeal Nerve Injury
Injury to the external branch of the superior laryngeal nerve is more common and often occurs during handling of the thyroid's upper pole due to inadequate separation or ligation involving the nerve and surrounding tissues.
External branch injury causes paralysis of the cricothyroid muscle, leading to vocal cord slackness and a reduced pitch.
Internal branch injury results in loss of sensation of the laryngeal mucosa, making patients prone to choking or coughing while eating or drinking. Most cases recover spontaneously with physiotherapy.
Hypoparathyroidism
Accidental removal or damage to the parathyroid glands, compromised blood supply, or other surgical factors can cause hypoparathyroidism, leading to postoperative hypocalcemia. The incidence of this complication is associated with surgical extent and frequency.
Manifestations include increased neuromuscular excitability, usually emerging 1–3 days postoperatively. Initial symptoms include a tingling or stiff sensation in the extremities and around the mouth. Severe cases may exhibit persistent muscle spasms in the face and extremities, sometimes accompanied by pain. In extreme cases, spasms in the larynx or diaphragm can lead to asphyxia and death.
Preventive measures include careful handling of the parathyroid glands during surgery, immediate examination of excised tissue for unintended parathyroid removal, and prompt autotransplantation into the sternocleidomastoid muscle if parathyroid tissue is identified.
Treatment of Hypocalcemia
Calcium supplementation is the most common treatment. Oral calcium is typically administered at doses of 500–1,000 mg of elemental calcium 2–3 times daily, with adjustments based on symptoms and blood calcium levels.
In cases of severe symptoms or prolonged recovery, calcitriol may be added to enhance calcium absorption in the intestines.
Severe hypocalcemia, such as tetany, may require intravenous calcium supplementation. Slow intravenous infusion of 10–20 ml of 10% calcium gluconate solution is an effective and well-tolerated approach to rapidly elevate calcium levels.
Thyroid Storm
Thyroid storm is a severe postoperative complication of hyperthyroidism caused by excessive release of thyroid hormones, leading to an acute adrenergic response. Clinical observations suggest that thyroid storms are related to inadequate preoperative preparation, poor control of hyperthyroid symptoms, and surgical stress. Proper preoperative preparation and careful surgical techniques are critical for prevention.
Most cases occur 12–36 hours postoperatively, presenting with acute onset and rapid progression. Key symptoms include high fever (above 39°C), tachycardia (over 120 bpm), and severe dysfunction of the nervous, circulatory, and digestive systems. These symptoms may involve restlessness, delirium, profuse sweating, vomiting, and diarrhea. Without timely management, the condition may progress rapidly to collapse, coma, shock, or even death, with a mortality rate of approximately 8–25%.
Treatment of Thyroid Storm
General Management
Use of sedatives, temperature reduction, adequate oxygen supply, and energy replenishment.
Maintenance of fluid, electrolyte, and acid-base balance. Sodium phenobarbital (100 mg) is commonly used as a sedative. Fever can be managed through antipyretics, hibernation-inducing agents, and physical cooling techniques to maintain body temperature around 37°C. Large volumes of intravenous glucose solution are used for energy replenishment.
Pharmacological Treatment
The treatment options include:
- Antithyroid medications such as propylthiouracil.
- Iodine preparations including compound potassium iodide or saturated potassium iodide solution.
- Beta-blockers like propranolol.
- Adrenal corticosteroids such as hydrocortisone.