The Diagnosis and Management of Hypothyroidism

Bhuvana Guha, MD, Guha Krishnaswamy, MD, And Alan Peiris, MD, PhD, MRCP

Disclosures

South Med J. 2002;95(5):475-480. 

In This Article

Diagnosis

The diagnosis of primary hypothyroidism is confirmed by a reduced free-thyroxine (T4) level and elevated thyroid-stimulating hormone (TSH) level. Subclinical hypothyroidism is diagnosed by the demonstration of elevated TSH levels in the setting of normal free-T4 levels.[9,10] The diagnosis of secondary hypothyroidism resulting from hypothalamic-pituitary dysfunction is more difficult, since the TSH level may be reduced, normal, or even slightly elevated in this condition.[11] Evaluation of other pituitary hormone levels (prolactin, growth hormone, cortisol, and gonadotropins) and imaging studies (computerized tomography or magnetic resonance imaging of the brain) may need to be considered.[11] A positive antithyroid antibodies test may indicate the presence of Hashimoto's disease, but usually does not influence management in frank hypothyroidism. The presence of antithyroid antibodies may also indicate the coexistence of subclinical or overt polyglandular autoimmune endocrine diseases.[1] The use of the thyrotropin-releasing hormone (TRH) test has declined, although it may have a role in demonstrating the exaggerated TSH re-sponse seen with preclinical hypothyroidism. Its use in differentiating causes of central hypothyroidism (pituitary vs hypothalamic) has been questioned. In many instances, concomitant laboratory abnormalities may provide additional clues to the diagnosis of hypothyroidism ( Table 3 ). Radiologic imaging is usually not indicated, except for hypothyroidism associated with retrosternal goiter. Thyroid uptake measurements and scintigraphic studies (using either technetium 99m or iodine 123) are rarely needed, but may occasionally assist in differentiating autoimmune thyroiditis from other diseases involving the thyroid.[12] In rare cases, histologic evaluation of thyroid tissue biopsies may be required in order to confirm the diagnosis.

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