The differential diagnosis of a patient with nodular goiter includes benign nodular goiter, Hashimoto's thyroiditis, follicular adenoma, and carcinoma.

The laboratory evaluation of a patient with a thyroid nodule or a nodular goiter should begin with a TSH measurement to determine whether the patient is euthyroid, hypothyroid, or hyperthyroid. The degree of thyroid dysfunction is often mild or subclinical, with only an isolated TSH abnormality. The diagnosis of thyrotoxicosis should be considered in all, but particularly in elderly, patients with long-standing nodular goiter and/or atrial fibrillation. In some, usually elderly, patients, the diagnosis of hyperthyroidism is not clinically apparent (apathetic hyperthyroidism). TSH is suppressed to a variable degree, and characteristically the plasma T3 level is elevated, whereas the plasma T4 level is normal (T3 thyrotoxicosis).

When the thyroid gland is only moderately enlarged and firm, Hashimoto's thyroiditis should be considered. A blood test documenting increased levels of antithyroid peroxidase antibodies or thyroglobulin antibodies helps confirm the diagnosis. Ultrasound often reveals a heterogeneous thyroid gland. FNA is helpful when there is a discrete nodule within the firm thyroid gland. Some clinicians recommend evaluating calcitonin levels in patients with nodular goiter, but most believe it is not cost-effective.64

A chest radiograph often brings attention to cervical or substernal goiter due to tracheal deviation. Occasionally, fine calcifications in a nodular goiter suggest the presence of a papillary carcinoma.

Ultrasound, as previously mentioned, is particularly helpful in patients who are to be followed to assess and monitor the size of a nodule or the goiter. Some clinicians recommend treating patients with small or moderate-sized euthyroid goiter with thyroid hormone. In about 25% of these patients, the goiter decreases in size, and in others, the growth rate may decrease (see Chapter 8). CT or MRI scanning of the neck and superior mediastinum in patients with substernal or fixed goiters may reveal tracheal deviation or compression (Fig. 4-3).65 66 Thyroid scintigraphy is not indicated for the assessment of nodular goiter unless the patient has a suppressed TSH or treatment with 13'I is being considered. Euthyroid patients with large goiters usually have low iodine uptake so that a large dose of radioiodine is required.

FIGURE 4-3. CT scan of a patient with a large goiter. Note the evidence of severe tracheal compression and deviation to the right side (arrow).

Such treatment is only rarely indicated but has recently been reported to be more effective than TSH suppression.67 Evidence of airway obstruction can be obtained by a flow-volume loop tracing. A barium swallow is rarely indicated unless other causes of dysphagia are considered.

The role of FNA has previously been discussed. We recommend FNA for selected patients with multinodular goiter who have a dominant nodule within a multinodular goiter, a large (>4 cm) nodule, nodules with ultrasonic features suggestive of malignancy, a rapidly enlarging nodule, and suspicious complex thyroid nodules (biopsy the solid component).

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