On the Endocrinology ward, two individuals came in. The first one is 23 year old Hannah who complains of lethargy, fatigue, reduced appetite, muscle weakness and constipation. She also says that lately she gained a bit of weight and has a low libido. On clinical examination, she has periorbital edema, dry, cool skin, her nails are brittle and her reflexes are slow. She also has a moderately enlarged, painless goiter. The other one is 33 year old Quentin, who also presents with lethargy, fatigue, reduced appetite, muscle weakness, constipation and he’s also complaining about feeling cold all the time. He said that he recently had the flu, but no other illnesses. On clinical examination, there’s periorbital edema, dry, cool skin, brittle nails and hair, and a very painful goiter. TSH, free T3 and T4 are taken, along with antithyroid-peroxidase and antithyroglobulin antibodies. Both Hannah and Quentin have high levels of TSH and low T3 and T4 levels, but Hannah has positive antithyroid-peroxidase and antithyroglobulin antibodies.
Both individuals seem to have hypothyroidism. First, a bit of physiology. Normally, the hypothalamus detects low serum levels of thyroid hormones and releases thyrotropin-releasing hormone or TRH into the hypophyseal portal system. The anterior pituitary then releases thyroid-stimulating hormone, also called thyrotropin or simply TSH. TSH stimulates the thyroid gland. The thyroid gland is made up of thousands of follicles, which are small spheres lined with follicular cells. Follicular cells convert thyroglobulin, a protein found in follicles, into two iodine-containing hormones, triiodothyronine or T3, and thyroxine or T4. Once released from the thyroid gland, these hormones enter the blood and bind to circulating plasma proteins. Only a small amount of T3 and T4 will travel unbound in the blood, and can act upon nearly every type of cell in the body. Once inside the cell T4 is usually converted into T3, and it can exert its effect. T3 speeds up the cell’s basal metabolic rate. It increases cardiac output, stimulates bone resorption, basically thinning out the bones, and activates the sympathetic nervous system. Thyroid hormones are also involved in a number of other things, like controlling sebaceous and sweat gland secretion, hair follicle growth, and regulating proteins and mucopolysaccharide synthesis by skin fibroblasts.