Thyroid Disorders

Thyroid disease is easier to recognize when thyrotoxicosis is separated from hyperthyroidism. Thyrotoxicosis means that tissues are exposed to too much thyroid hormone. Hyperthyroidism means the thyroid is actively synthesizing and releasing excessive hormone. Graves disease and toxic nodular disease cause hyperthyroidism; thyroiditis and excess exogenous hormone cause thyrotoxicosis without increased synthesis. In Graves disease, stimulating antibodies directed at the TSH receptor—called TRAb or TSI—activate the receptor despite suppressed pituitary TSH. The thyroid continues producing and releasing T4 and T3, often with diffuse enlargement. The same antibody-driven process can activate orbital fibroblasts, producing extraocular muscle and orbital tissue expansion, proptosis, diplopia, and, in some patients, dermopathy. Toxic multinodular goitre produces hormone from autonomously functioning nodules. Hormone production becomes independent of pituitary control, so TSH is suppressed but only portions of the gland are overactive. Hashimoto thyroiditis has the opposite trajectory: lymphocytic inflammation progressively destroys follicular cells and reduces hormone production. Anti-TPO antibodies are present in approximately 95% of cases; anti-thyroglobulin antibodies occur in about 60–80%. Early destructive inflammation can briefly release stored hormone, causing a thyrotoxic phase before hypothyroidism develops....