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In the Clinic |


Michael T. McDermott, MD
Ann Intern Med. 2009;151(11):ITC6-1. doi:10.7326/0003-4819-151-11-200912010-01006
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Hypothyroidism is a condition in which the thyroid gland cannot make enough thyroid hormone to meet the requirements of peripheral tissues. It is the most common functional disorder of the thyroid gland. Primary hypothyroidism occurs when thyroid failure results from disease of the thyroid gland itself and it accounts for more than 99% of all cases of hypothyroidism (Figure 1). The most common causes of primary hypothyroidism in adults are chronic lymphocytic thyroiditis (Hashimoto disease); radioiodine thyroid ablation; thyroidectomy; high-dose head and neck radiation therapy; and medications, such as lithium, α-interferon, and amiodarone. Central hypothyroidism occurs when thyroid failure results from pituitary or hypothalamic disorders that cause insufficient production of thyroid-stimulating hormone (TSH) by the pituitary gland (Figure 2). The most common causes of central hypothyroidism in adults are tumors, inflammatory conditions, infiltrative diseases, infections, pituitary surgery, pituitary radiation therapy, and head trauma.

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Grahic Jump Location
Figure 1.

Hormone changes occurring during the development of primary hypothyroidism.

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Grahic Jump Location
Figure 2.

Hormone changes occurring during the development of central hypothyroidism.

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Grahic Jump Location
Figure 3.

The effect on free T4 of fine adjustment of LT4 doses in patients with primary hypothyroidism.

Reprinted with permission from Carr D, McLeod DT, Parry G, Thornes HM. Fine adjustment of thyroxine replacement dosage: comparison of the thyrotrophin releasing hormone test using a sensitive thyrotrophin assay with measurement of free thyroid hormones and clinical assessment. Clin Endocrinol (Oxf). 1988;28:325-33.

Grahic Jump Location




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