Thyroid Nodules
The prevalence of thyroid nodules increases markedly with age. Even in iodine-sufficient regions (all of the USA), about 80% of persons >70 have one or more thyroid nodules based on gross pathologic examination, and during life 45% show nodules by ultrasonography and about 10% by palpation.
Radiation-induced cancer does not appear to occur after latent periods of > 50 years; therefore, a history of radiation to the face, neck, or thorax in childhood is probably not relevant in elderly patients.
Symptoms, Signs, and Diagnosis
Findings are similar in the elderly and in younger persons. A nodule may be merely an enlarged lobe, a lobule in a diffuse goiter, or a pyramidal lobe. Nodules may also be regenerating areas after subtotal resection of the thyroid, localized subacute or chronic thyroiditis, cysts, or hemorrhage and calcification in a colloid adenoma. Concern about malignancy may be lower if the dominant nodule is not the only one, if both lobes are abnormal on palpation, or if the history reveals a sudden appearance with pain and tenderness, suggesting hemorrhage in a degenerating colloid adenoma.
Hashimoto's disease causes the gland to feel very firm with multiple small nodules. Colloid adenomas may be softer than normal, although their consistency varies from patient to patient. Tenderness suggests hemorrhage into a colloid adenoma. Fluctuation suggests cystic changes, but these are more likely to result from hemorrhage or necrosis of a colloid adenoma than from a simple water-clear cyst.
Anaplastic carcinoma often has features that clearly suggest malignancy. The patient has a large, growing, stony hard thyroid mass that is irregular, immobile, and fixed to other tissues. Also, the patient may be hoarse.
Evaluation of thyroid nodules remains controversial, regardless of the patient's age. Most experts recommend at least a fine-needle aspiration, which has high sensitivity and specificity for a cancer diagnosis. Thyroid function tests are usually normal except with the relatively uncommon hyperfunctioning nodule, in which case serum T4 and T3 levels may be high and serum TSH may be subnormal or undetectable. When these findings are obtained, a radionuclide scan should be performed to prove that the nodule is functioning. When results of thyroid function tests are normal, a radionuclide scan is often performed to exclude a functioning lesion, which is almost always benign, and ultrasonography is performed to identify simple cysts, also usually benign. However, these expensive procedures have a low diagnostic yield because of their extremely poor specificity for malignancy.
Serum thyroglobulin measurement has low specificity. X-rays of microcalcifications, representing psammoma bodies, have low sensitivity but high specificity for the diagnosis of papillary adenocarcinoma. Elevated antithyroid antibodies suggest Hashimoto's disease as the cause of nodularity but cannot rule out a coexisting carcinoma, so fine-needle aspiration is indicated for the dominant nodule.
Prognosis and Treatment
Most nodules are benign or behave benignly, even if they appear malignant on histologic examination. The 5-year survival rate for all patients with thyroid cancers is 93%, which is comparable with the average survival of the age-adjusted population. In elderly patients, nodules tend to be somewhat more invasive and malignant, but most are still papillary or papillofollicular and have excellent prognoses.
Surgery is indicated when fine-needle aspiration indicates cytologic evidence of or suspicion of malignancy unless concomitant medical conditions absolutely contraindicate it. If the physician doubts the cytologic impression (eg, the cytologist can diagnose a follicular neoplasm but usually cannot tell if it is benign or malignant), a better treatment choice is levothyroxine sodium to suppress TSH to subnormal (ie, 0.1 to 0.4 mU/L) but not to the point that the patient becomes hyperthyroid. Another fine-needle aspiration should be performed in 6 to 12 months. Overall, 6% of thyroid nodules are malignant, and 25% of those with suspicious cytologic results are malignant.
If thyroid cancer is discovered during surgery, the next step is controversial. Most physicians recommend a near-total thyroidectomy followed by 131I therapy to ablate the remainder. Then a total body scan is performed to search for residual tissue capable of capturing 131I. If the results are positive, a therapeutic dose of 50 to 150 mCi is administered. Although it has a logical rationale and is widely accepted, this approach has not proved to be superior to near-total thyroidectomy alone; its alleged advantage derives from nonrandomized studies with possible selection bias.
At all times, except when preparing for a radionuclide scan or a therapeutic dose of 131I, the patient should receive long-term treatment with levothyroxine sodium as described above. Long-term TSH-suppressive therapy may cause accelerated osteoporosis and cardiac abnormalities if thyrotoxic doses are given. |
