USMLE® Step 1 style questions USMLE
A 34-year-old man comes to the clinic with hoarseness and difficulty breathing and swallowing for the past 2 weeks. He denies weight gain and fatigue. Physical examination shows a hard, diffuse, immovable neck goiter that is painless to palpation. Fine needle aspiration shows fibrous tissue with inflammatory infiltrate. Which of the following is the most likely diagnosis?
So, Riedel’s thyroiditis is a condition where there is inflammation of the thyroid gland, which slowly causes fibrous tissue to replace the normal thyroid tissue.
The condition is named after the German surgeon - Dr. Bernhard Moritz Carl Ludwig Riedel who first described it.
Normally, the hypothalamus, which is located at the base of the brain, secretes thyrotropin-releasing hormone, or ΤRH, into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior pituitary gland.
The anterior pituitary then releases a hormone of its own, called thyroid-stimulating hormone, thyrotropin, or simply TSH.
TSH stimulates the thyroid gland, which is a gland located in the neck that looks like two thumbs hooked together in the shape of a “V”.
If we zoom into the thyroid gland, we’ll find thousands of follicles, which contain a sticky substance called colloid, which sits within follicular cells.
Follicular cells convert the protein thyroglobulin into two iodine-containing hormones, triiodothyronine or T3, and thyroxine or T4.
Once released from the thyroid gland, these hormones enter the blood and the majority is bound to circulating plasma proteins, with only a small amount of T3 and T4 traveling unbound in the blood.
Ultimately, these two hormones get picked up by nearly every cell in the body.
Once inside the cell T4 is mostly converted into T3, and it can exert its effect. T3 speeds up the basal metabolic rate.
T3 increases cardiac output, stimulates bone resorption - thinning out the bones, and activates the sympathetic nervous system, the part of the nervous system responsible for our ‘fight-or-flight’ response.
Thyroid hormone is important - and the occasional increase can be really useful when you need a boost to get through the final rounds of a sporting competition or to stay warm during a snowstorm!
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.
It’s not entirely clear why, but sometimes the immune system begins to attack certain organs and tissues.
More specifically, there’s a pattern of autoimmune diseases that involves T cells and plasma cells that overproduce a specific type of IgG antibody called IgG4, going rogue and attacking multiple organs like the thyroid, pancreas, lacrimal or tear glands, and salivary glands.
When the thyroid is severely affected it’s called Riedel’s thyroiditis.
In Riedel’s thyroiditis, we don’t know what IgG4 antibodies do exactly, but we do know that the T cells release cytokines that attract macrophages and neutrophils which in turn damage the thyroid follicles.