Determine Who’s At Risk | Clinical Evaluation | Risk Communication | Specialists | Treatment and Management

Clinical Evaluation

Because I-131 concentrates in the thyroid gland, evaluation of a patient exposed to I-131 centers on diseases of the thyroid. Exposure to I-131 can cause thyroiditis, hypothyroidism, and thyroid neoplasms. The patient might have a variety of symptoms related to exposure or might have health-related concerns about past exposure. The occurrence of thyroid diseases caused by exposure is indistinguishable from those that occur spontaneously. The patient might not have specific knowledge of the nature of the exposure, which might have occurred years earlier. It is important to note that I-131 can also be used therapeutically to treat some types of thyroid disorders. For information on therapeutic uses of I-131, consult the American Association of Clinical Endocrinologists at www.aace.com. For an evaluation guide, click here.

A history and appropriate physical examination supplemented with laboratory investigation, imaging studies, and fine-needle aspiration biopsy (FNAB) of the nodules in question should provide the clinician with sufficient information to assess the likelihood of malignancy and to advise his or her patients of appropriate treatment options.

Ultrasound can find many nodules not palpable during the physical examination. Ultrasound is being used for thyroid monitoring programs in other countries where some of the population has been exposed to I-131 releases. However, the use of thyroid ultrasound in mass screenings for thyroid nodules is controversial because of its high sensitivity and low specificity.

If a nodule is identified, fine-needle aspiration biopsy (FNAB) performed by an experienced physician with appropriate training and experience is the procedure of choice. If the cytology of the nodule is malignant or nondiagnostic, the patient should be referred to a specialist for surgical resection.

History and physical exam should focus specifically on signs and symptoms related to the thyroid gland.

The medical history should include prior endocrine, thyroid, or parathyroid problems; prior thyroid diagnostic tests and treatments; and history of thyroid or neck surgery. Information about changes in the size of the nodule or nodules can assist in determining the etiology. Nodules that are unchanged for years are probably benign, but nodules that grow rapidly demand careful evaluation and are more likely to be associated with parathyroid disorders.

A family history of Hashimoto thyroiditis, benign thyroid nodule, or goiter favors a diagnosis of benign disease. Other history that suggests benign disease includes symptoms of hypothyroidism or hyperthyroidism, and pain or tenderness of the nodule. Risk factors for malignant disease can include a family history of thyroid carcinoma or multiple endocrine neoplasia type II; the patient’s age (<20 years or >70 years); the patient’s gender (male); recent changes in voice, breathing, or ability to swallow; and a childhood history of head, neck, or upper mediastinum radiation exposure.

An exposure history includes previous childhood head, neck, and upper mediastinum radiation exposure; previous residences (downwind from or proximity to nuclear testing or release sites); dietary habits since childhood; source of drinking water; occupational history; and hobbies. Milk consumption and source are important risk factors (for example, fresh versus processed milk; milk from a cow, sheep, or goat). The patient should be asked about symptoms consistent with hypothyroidism, hyperthyroidism, and disorders of calcium metabolism.

Exposure to I-131 could be indicated by the patient’s answers to questions in the exposure history relating to the following:

• previous childhood head, neck, and upper mediastinum radiation exposure;
• previous residences;
• dietary habits since childhood; and
• milk consumption and source.

Populations exposed to I-131 can have a higher prevalence rate for thyroid nodules than populations that have not been exposed. Patients, especially infants and children who have been exposed to significant doses of I-131, are more susceptible to the associated negative health effects. The major clinical concerns after significant I-131 exposure include hypothyroidism and thyroid cancer.

Exposure History Form

Exposure History Taking: Sample Questions

Case Studies in Environmental Medicine: Taking an Exposure History (ATSDR)

Physical examination of the neck and thyroid should evaluate the gland’s size, presence of nodules, and the cervical lymph nodes. The thyroid gland should be inspected for shape, consistency, and areas of tenderness. Local examination of the neck is best accomplished with the patient seated in good light with the neck moderately extended. To facilitate the examination, the patient should be given a glass of water to assist swallowing. Auscultation of the neck provides some indication of the vascularity of the gland. A systolic or continuous bruit is usually associated with hyperthyroidism. The parathyroid glands are also susceptible to the effects of I-131 exposure. The presence of cervical lymphadenopathy, especially in children, might be the first sign of thyroid cancer. In general, a nodule 1 centimeter (cm) or greater should be palpable on physical examination.

Signs and symptoms that should prompt concern include rapid enlargement of a previous or new thyroid nodule, unilateral vocal cord paralysis, dysphagia, and dyspnea. A solitary nodule in an otherwise normal gland should raise the suspicion of thyroid carcinoma. A lesion is probably malignant if it is adherent to the surrounding structures (trachea or strap muscles). Palpable cervical lymphadenopathy adjacent to a thyroid nodule is suspicious for a carcinoma, or it might be the only indication of metastatic thyroid cancer when no thyroid nodule is palpable.

• Initial laboratory evaluation should include a serum thyroid stimulating hormone (TSH) level.

No evaluation of the thyroid gland is complete without a structural assessment (physical exam) and a functional assessment (blood analysis to determine the TSH level). Thyroid function tests are mandatory for evaluation of a thyroid nodule; however, these tests do not differentiate between benign and malignant nodules.

• Screening patients for thyroid effects of I-131 is different from evaluating a known thyroid nodule.

In screening programs, it is important to test for the noncancerous effects of I-131. The serum TSH level should be obtained to identify those patients with thyroid gland dysfunction. If TSH is abnormal, serum free thyroxine (FT4) and levothyroxine (T3) levels should be measured. Most patients with thyroid cancer are euthyroid (their thyroid glands function normally), and it is rare for a patient with thyroid cancer to have an abnormal TSH level.

Chronic autoimmune thyroiditis can be found with an increased TSH level and a thyroid nodule or bilateral nodules. Serum antithyroid peroxidase antibody and antithyroglobulin antibody levels can assist in the diagnosis of chronic autoimmune thyroiditis. However, the diagnosis of chronic autoimmune thyroiditis does not exclude the presence of cancer within the thyroid gland. Serum calcium levels should be assessed because of the risk for hyperparathyroidism after I-131 exposure. If the calcium level is abnormal, measure parathyroid hormone and phosphorus.

Ultrasound is useful to determine the size and physical characteristics of a nodule once it has been identified. However, ultrasound cannot differentiate benign from malignant nodules and therefore is not required in the evaluation of a palpable thyroid nodule.

Figure. Evaluation of a Euthyroid Nodule

Fine Needle Aspiration Biopsy

• Fine needle aspiration biopsy is the procedure of choice for evaluating whether or not a thyroid nodule is malignant.

The challenge to clinicians is to distinguish benign nodules from malignant tumors. The prevalence of clinical thyroid cancer in the general population is significantly less than 1%, and the majority of nodules are benign. Fine needle aspiration biopsy (FNAB) is the procedure of choice for evaluating a palpable nodule. The technique is simple and generally free of complications when performed by an experienced physician with appropriate training. If a nodule is found with ultrasound, the physician must differentiate between a simple cyst and a complex cyst. A simple cyst will require followup. A complex cyst must undergo an FNAB. If the results of the cytologic examination indicate the nodule is benign, no further testing is required but followup should be on an annual basis. Nondiagnostic results call for a repeat of the FNAB. Diagnosis of a malignancy or a probable malignancy requires surgery. The figure above illustrates the process of nodule evaluation.

FNAB is reportedly superior to all other techniques for diagnosing thyroid cancer. The use of FNAB can reduce the number of unnecessary surgical operations for suspicious nodules that prove to be benign. It is also the procedure of choice for evaluating a complex cyst after it has been identified on ultrasound imaging of the thyroid gland. Very few palpable thyroid nodules are actually simple cysts (defined as a cystic structure with no internal echoes and no evidence of thickening of the cyst wall). Most palpable thyroid nodules are solid nodules with cystic components. A simple cyst is almost always benign. Occasionally, cancer is found in the wall of the cyst. For this reason, recurrent cysts should be imaged by ultrasound. Surgical evaluation is indicated if evidence exists for a separate lesion or growth in the wall of the cyst.

FNAB for cytology with ultrasound guidance is often a diagnostic procedure; when the nodule is cystic, FNAB might also be curative. A satisfactory aspirate specimen combined with an accurate cytology evaluation by a cytopathologist provides a reliable means of differentiating between a benign and malignant nodule in all but highly cellular or follicular lesions. FNAB does not allow for differentiating Hashimoto disease from lymphoma of the thyroid. This can be done using a combination of FNAB cytology and clinical evaluation. A “nondiagnostic” specimen should be followed up with a repeat FNAB. A nodule that gives persistently nondiagnostic FNAB results should be surgically removed. In general, 20% to 30% of patients are referred for surgical evaluation on the basis of FNAB cytologic features.

Diagnosis and classification of thyroid cancers are performed by cytology. The most efficient way of screening for thyroid malignancy in a patient is to elicit a thorough history and perform a careful physical examination, followed by an FNAB and interpretation of the specimen by an experienced cytopathologist. Neck ultrasound is an ideal technique for establishing whether a palpable cervical mass is within or adjacent to the thyroid, and for differentiating thyroid nodules from other neck masses such as cystic hygromas, thyroglossal duct cysts, and enlarged lymph nodes. Papillary thyroid cancer is the most common type of cancer found among the population exposed to I-131 releases in Chernobyl.