Subtotal Thyroidectomy for Graves’ Disease
Edwin L. Kaplan
Raymon H. Grogan
DEFINITION
Subtotal thyroidectomy means the removal of most of both lobes of the thyroid, but some thyroid tissue is intentionally left on one or both sides of the neck.
Total thyroidectomy alone or with appropriate neck dissections is the procedure of choice for most thyroid cancers and is discussed in Part 5, Chapter 36.
Thyroid lobectomy is used for some unilateral benign colloid nodules or goiters and for many indeterminate thyroid lesions; that is, when the fine needle aspirate demonstrates a possible follicular neoplasm or a follicular lesion of undetermined significance (FLUS) that requires operation (see Part 5, Chapter 35).
Subtotal thyroidectomy is frequently used in the treatment of benign thyroid diseases such as nontoxic or toxic multinodular goiters, especially when the disease is bilateral and commonly in the treatment of Graves’ disease, although near-total or total thyroidectomy may be more appropriate in some patients.
The purpose of subtotal thyroidectomy is to reduce the incidence of postoperative complications of total thyroidectomy—permanent hypoparathyroidism and recurrent laryngeal nerve injury—and to leave functional thyroid tissue in the neck of some patients. Although the rate of complications of total thyroidectomy is low in the hands of expert thyroid surgeons, most surgeons would agree and most studies have demonstrated a lower incidence of complications when subtotal thyroidectomy is performed.
This section will briefly discuss the diagnosis and preoperative assessment of patients with benign thyroid conditions and will illustrate the preoperative management and surgical technique when performing a subtotal thyroidectomy for Graves’ disease.
PATIENT HISTORY AND PHYSICAL FINDINGS
In order to differentiate these benign thyroid conditions, a careful history and physical examination are first necessary.
History: Of greatest importance is a previous history of lowdose (or high-dose) radiation to the neck, which is associated with an increased risk of thyroid cancer. Also important are the metabolic status of the patient and whether or not there are symptoms of respiratory impairment, pressure on the trachea, or difficulty swallowing from an enlarged thyroid or from thyroid nodules.
Major symptoms of hypothyroidism
Severe fatigue, weight gain, dry skin, irregular menstrual periods, constipation, depression, hair loss, brittle nails, feeling cold, slowness of speech, and puffiness. In its most severe form, hypothyroid coma may rarely occur.
Major symptoms of hyperthyroidism (thyrotoxicosis)
Weight loss despite a normal or an increased appetite, rapid or irregular heartbeat, nervousness, anxiety, irritability, tremor, sweating, changes in menstrual pattern, increased sensitivity to heat, more frequent bowel movements, fatigue, muscle weakness, difficulty sleeping, and fine brittle hair. In its most severe form, thyroid storm might occur.
Respiratory and compressive changes and difficulty swallowing
Nodules of the thyroid or an enlarged thyroid (goiter) may cause pain and tenderness in the neck as well as trouble breathing. As the thyroid enlarges, the trachea can be compressed and narrowed and eventually respiratory impairment may occur resulting in coughing, shortness of breath, and stridorous breathing. Rarely, an enlarged goiter can result in recurrent laryngeal nerve impairment with hoarseness. Pressure from a goiter or from thyroid nodules can also result in trouble swallowing.
Physical findings
The physician should assess the size of the thyroid gland and the size, consistency, number, and position of any thyroid nodules; whether or not the trachea is deviated; and if any enlarged and abnormal lymph nodes are present in the central or lateral neck. Finally, the physician should assess whether there are any signs of thyrotoxicosis in general or evidence of manifestations of Graves’ disease such as exophthalmos, pretibial myxedema, and a diffuse goiter with a bruit.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Thyroid function tests
Almost all patients with hypothyroidism have an elevated thyrotropin (TSH) level with low free thyroxine (FT4) and triiodothyroxine (T3) values.
Almost all thyrotoxic patients have a suppressed TSH with elevated FT4 and T3 values.
Tests for autoimmunity
In Hashimoto’s disease and Graves’ disease, antibodies to thyroid peroxidase (anti-TPO antibodies) are found in up to 90% of patients, whereas antithyroglobulin (anti-TG) antibodies are found in approximately 50%. Elevated anti-TSH receptor antibodies (TSab) are also commonly detected in patients with Graves’ disease and these thyroid-stimulating immunoglobulins (TSI) are the cause of the thyrotoxicosis of Graves’ disease.
Imaging and nuclear uptake scanning
The thyroid uptake of radioiodine or technetium isotopes is usually increased in toxic multinodular goiter, toxic adenoma, and Graves’ disease.
Nuclear scans may help to differentiate each of these diseases.
With toxic multinodular goiter, an enlarged thyroid gland is noted with one or more “hot” areas usually among other “cold” areas.
Toxic adenoma. A single hot area is clearly seen which corresponds to the thyroid nodule. The remaining thyroid
tissue is suppressed and barely visualized on the scan.
Graves’ disease. Both lobes of the thyroid demonstrate increased uptake of isotope on the scan.
Other imaging studies
Ultrasound examinations are commonly used to evaluate the thyroid for nodules and to identify abnormal lymph nodes and have replaced a nuclear scan unless a hot nodule is suspected.
Computerized tomography (CT) scan and magnetic resonance imaging (MRI) exams are helpful to evaluate the presence or absence of tracheal compression; abnormal lymph nodes; or the presence, size, and anatomic location of a substernal goiter. These are often reserved for goiters that extend below the clavicle or if significant tracheal narrowing is of concern.
The most important test to evaluate a thyroid nodule is a fine needle aspiration (FNA) with cytologic examination. This exam should be used liberally. Usually, it is performed under ultrasound guidance in order to be certain that the nodule in question has correctly been sampled.
DIFFERENTIAL DIAGNOSIS
A short list of common benign thyroid conditions:
Thyroid abnormalities associated with normal thyroid function or hypothyroidism
Single colloid nodule or cyst
Single microfollicular or macrofollicular adenoma
Multinodular goiter
Hashimoto’s thyroiditis
Thyroid abnormalities associated with thyrotoxicosis
Toxic adenoma
Toxic multinodular goiter
Graves’ disease
Graves’ disease is an autoimmune disease characterized by a goiter, thyrotoxicosis, and exophthalmic eye disease. Less commonly, pretibial myxedema is also present. It is closely related to Hashimoto’s thyroiditis, which usually presents with hypothyroidism.
It was described first in the English language by Caleb Perry (1755-1822) but commonly bears the name of the Irish physician, Robert Graves. On the European continent, it is called Basedow’s disease.
As an autoimmune thyroid disease, it exhibits both antibodies and cell-mediated immunity directed to thyroid peroxidase (TPO) and thyroglobulin (TG) as well as stimulating antibodies against the TSH receptor (called TSab, but formerly called long-acting thyroid stimulator [LATS]). Antibodies against eye muscle and fibroblasts are also found in the serum of same patients with severe Graves’ ophthalmopathy.
Incidence of Graves’ disease
Found in women 5 to 8 times more commonly than in men
Thirty cases per 108,000 population annually in Ohmstead County, Minnesota
Increases in incidence during each decade from adolescence to 60 years of age
Six percent of all Americans have autoimmune thyroid disease.
SURGICAL MANAGEMENT
A thyroidectomy is usually indicated for the following reasons:
To treat thyroid malignancies and some benign thyroid nodules
To establish a definitive diagnosis when diagnosis by FNA is equivocal, nondiagnostic, or indeterminate
To alleviate pressure symptoms or respiratory difficulties associated with a malignant or a benign process
To remove a substernal goiter
To remove an unsightly goiter
As definitive therapy for individuals with thyrotoxicosis— selected patients with hot nodules, toxic multinodular goiter, and Graves’ disease
Preparation for surgery
Most patients undergoing a thyroid operation are euthyroid and require no specific preoperative preparation related to their thyroid gland. Determination of serum calcium and parathyroid hormone (PTH) levels may be helpful. Endoscopic or indirect laryngoscopy might be helpful for all patients preoperatively but definitely should be done in those who are hoarse or who have had a change in voice and in others who have had a prior thyroid, parathyroid, carotid, lateral neck, anterior cervical disc, or chest operation in order to detect the possibility of a recurrent laryngeal nerve injury.
Hypothyroidism
Modest hypothyroidism is of little concern when treating a surgical patient; however, severe hypothyroidism can be a significant risk factor. Severe hypothyroidism can be diagnosed clinically by myxedema as well as by slowness of affect, speech, and reflexes. Circulating thyroxine and triiodothyronine values are low. The serum TSH level is high in all cases of hypothyroidism that are not caused by pituitary insufficiency. In the presence of severe hypothyroidism, both the morbidity and the mortality of surgery are increased as a result of the effects of both the anesthesia and the operation. Such patients have a higher incidence of perioperative hypotension, cardiovascular problems, gastrointestinal hypomotility, prolonged anesthetic recovery, and neuropsychiatric disturbances. They metabolize drugs slowly and are very sensitive to all medications. Therefore, when severe myxedema is present, it is preferable to defer elective surgery until a euthyroid state is achieved.
Hyperthyroidism
Toxic multinodular goiter and a toxic adenoma are usually treated to a euthyroid state with an antithyroid medication such as methimazole (Tapazole) or propylthiouracil (PTU), and the possible use of a beta-adrenergic blocker such as propranolol. Radioiodine therapy may sometimes be used as definitive therapy.
Operative therapy for a toxic multinodular goiter is usually a subtotal or total thyroidectomy. For a toxic adenoma, enucleation of the nodule or a thyroid lobectomy is curative because a hot nodule is almost always benign. This can be confirmed preoperatively by FNA evaluation. Furthermore, because most of the thyroid tissue remains after enucleation, the majority of patients become euthyroid postoperatively without the need for thyroid hormone replacement.
Treatment of patients with Graves’ disease
In the United States, most patients with thyrotoxicosis have Graves’ disease. Furthermore, in the United States,
over 90% of all patients with Graves’ disease are treated with radioiodine therapy.
Operative indications for Graves’ disease may include very young patients, others with very large goiters, some pregnant women, and those with suspicious thyroid nodules or severe ophthalmopathy.
For greatest safety, patients with Graves’ disease should be treated preoperatively with PTU or methimazole and iodine drops to restore a euthyroid state and to prevent thyroid storm. Thyroid storm is the name for the most severe manifestations of thyrotoxicosis including a very rapid heart rate or cardiac arrhythmias, fever, disorientation, hypotension, coma, and even death. In the past, mortality of thyroid storm was very high, but now, with the use of beta-blockers, antithyroid medications, iodine, oxygen, glucose, possibly adrenocortical steroids, and intensive care measures, the death rate has been greatly reduced. Both anesthesia and operation on a poorly prepared thyrotoxic patient are the leading precipitating factors for this event. Furthermore, operation on an unprepared Graves’ gland can be more difficult because severe bleeding may occur because the thyroid is often soft and very vascular. With proper preoperative preparation, however, operation on the thyroid gland in Graves’ disease can be performed safely.
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