The diagnostic evaluation of the patient with thyromegaly will be determined by the clinical history and an examination of the thyroid gland (Table 9). In most instances the diagnosis will not be in doubt, and only a few tests will be necessary. For example, the euthyroid adolescent female with an asymmetrically or symmetrically enlarged, firm thyroid gland has a presumptive diagnosis of CLT, and only tests of thyroid function (T4 and TSH) and thyroid antibodies may be needed for confirmation. Similarly, the patient with clinical symptoms and signs of hyperthyroidism, exophthalmus, and a diffusely enlarged, soft thyroid gland has a presumptive diagnosis of Graves disease. The necessary tests include only a measurement of T4, an estimate of free T4, and WBC and differential counts prior to the initiation of antithyroid drug therapy.
[See table in the PDF file]
In the absence of an obvious diagnosis, the clinician will select the specific diagnostic tests depending upon the examination of the thyroid gland. The cause of smooth, symmetrical, diffuse enlargement of the thyroid gland can be suspected with careful history for familial disease, history of exposure to goitrogens and goitrogenic drugs, and the determination of thyroid antibodies in serum. If the clinical history is suggestive of hyperthyroidism, the tests of thyroid function tests should include determination of serum T3 concentration; if the history is compatible with euthyroidism or hypothyroidism, thyroid function tests should include determination of serum TSH concentration for the presence of compensated primary hypothyroidism. If results of these tests are normal, no additional tests are necessary, and the patient should be reassured and seen again in six months.
If the patient has a test that is negative for thyroid antibodies and an elevation of serum TSH concentration, a radioactive [123I]iodide uptake and perchlorate discharge test will be helpful in the diagnosis of familial dyshormonogenesis. The patient with constitutional symptoms of inflammatory disease, history of a recent upper tract respiratory infection, and a tender or nontender enlarged thyroid gland may have subacute thyroiditis; a low or absent uptake of radioiodine with high-normal or elevated T4 and T3 concentrations will be suggestive of that diagnosis.
In patients with thyromegaly and mild symptoms of hyperthyroidism, a TRH test will help to discriminate hyperthyroxinemia secondary to increased or abnormal serum thyroxine binding proteins from early Graves disease, factitious hyperthyroidism, toxic thyroiditis, and TSH-mediated hyperthyroidism. The T3 suppression test is a definitive diagnostic test for early, mild Graves disease.
The euthyroid patient with mild-to-moderate thyromegaly and tests that are negative for thyroid antibodies usually deserves no further diagnostic evaluation, but should be followed with a presumptive diagnosis of idiopathic goiter or mild CLT. On follow-up evaluation, initially at six-month intervals and subsequently at yearly intervals, the patient should have a clinical and biochemical assessment until thyromegaly regresses and the gland is normal in size and consistency.
The patient with a nontender, firm, irregular enlargement of the thyroid gland usually has CLT. If results of thyroid function tests are normal and tests for thyroid antibodies are negative, the patient should be seen again in four to six months and serum thyroid antibody determinations again performed. Another test that may give abnormal results in patients with CLT is the perchlorate discharge test.
The approach to the patient with the solitary thyroid nodule differs from that of the previously described clinical presentations. The most important studies for the patient with a thyroid nodule are those designed to determine the structure and consistency of the thyroid gland, namely, ultrasonography to distinguish between solid and cystic lesions, and the radionuclide scan to determine whether the nodule is functioning (hot) or nonfunctioning (cold). To assure that the thyroid nodule is not associated with a nonsurgical lesion such as Hashimoto thyroiditis, serum thyroid antibody determinations are important. As malignancy of the thyroid gland is usually not associated with abnormalities of thyroid function, it is important to perform laboratory tests to exclude hyperthyroidism (a serum T3 determination) and hypothyroidism (a serum TSH determination) at the time of initial evaluation. Additional tests are usually not necessary unless the patient had mild hyperthyroidism with an autonomously functioning nodule, in which case the T3 suppression test and TRH test are often useful; rarely, the TSH stimulation test is helpful in determing whether thyroid tissue throughout the remainder of the gland is suppressed. A solitary, solid, nonfunctioning (cold) nodule requires excisional biopsy.
THE DETERMINATION OF THYROXINE IN THE THYROID GLAND OF THE RAT
