Disorders of the Thyroid Flashcards
Overview of Thyroid hormones production
TSH is secreted from the anterior pituitary into circulation where it binds to its receptor on the thyroid follicular epithelium resulting in activation of adenylyl cyclase and cAMP via Gs activation leading to T4 and T3 production. In circulation, T4 and T3 are bound to carrier proteins such as TBG to their target organs where the effects of T3 predominate and bind to nuclear thyroid hormone receptors
The thyroid gland follicles also contain a population of parafollilcular, or C, cells. What is their function?
These synthesize and secrete the hormone calcitonin which promotes absorption of calcium by the skeletal system and inhibits osteoclast activity
Hypothyrodism is more common in what patient populations?
Much more common in the elderly and in women
What are the symptoms of hypothyroidism?
Fatigue, weakness, feeling cold and cold intolerance, constipation, hair and memory loss, weight gain with poor appetite, and menorrhagia (abnormally heavy bleeding)
What are the signs of hypothyroidism?
dry, coarse skin, puffy extremities or face (myxedema), alopecia, bradycardia, cavity effusions, carpal tunnel syndrome, and delayed tendon reflexes
What are the symptoms of hyperthyroidism?
hyperactivity, irritability, heat intolerance and sweating, palpitations, weight loss with increased appetite (in severe cases), diarrhea, loss of libido, fatigue and weakness
What are the signs of hyperthyroidism?
tremor, tachycardia/palpitations, goiter, warm skin, lid retraction, muscle weakness, pretibial myxedema (Grave’s disease)
How is hypothyroidism treated?
hormone replacement and in severe hypothyroidism, replace corticosteroids first because the adrenals cannot handle the increase in metabolism that will degrade circulating catecholamines
Half-lives of the thyroid hormones?
T4- 8 days
T3- 24 hrs
NOTE: It takes 4-5 half-lives to reach steady state (roughly 5 weeks in hypothyroidism patients in which you’d replace T4)
What is thyrotoxicosis?
A hypermetabolic state caused by elevated levels of free T4 and T3 that is commonly referred to as hyperthyroidism but may also be due to excessive release of preformed thyroid hormone (as in thyroiditis) or to an extrathyroidal source, rather than gland hyperactivity
What are the most common causes of hyperthyroidism?
- Diffuse hyperplasia of the thyroid associated with Graves disease (85%)
- Hyperfunctional multinodular goiter
- Hyperfunctional thyroid adenoma
Why does the skin of patients with hyperthyroidism tend to be warm, soft, and flushed?
Because there is increase blood flow and peripheral vasodilation that facilitate heat loss once the BMR is elevated. Often times, sweating and heat intolerance are common and there is a weight loss despite increased appetite
What is one of the earliest consistent manifestations of hyperthyroidism?
Elevated cardiac contractility and CO in response to increased peripheral oxygen demands can lead to tachycardia, palpitations, and cardiomegaly and can progress to a-fib or left-ventricular dysfunction
Why would diarrhea be a symptom of hyperthyroidism?
sympathetic hyperstimulation results in hypermotility and diarrhea
Other symptoms of hyperthyroidism?
Thryoid hormone stimulates bone resorption with a net effect of osteoporosis and an increased risk of fracture
What is a thyroid storm? Tx?
Refers to the abrupt onset of severe hyperthyroidism most commonly seen in patients with underlying Graves disese and most likely is the result of acute elevation in catecholamine levels subsequent to infection, surgery, or other forms of stress. Pts. are typically febrile with intense tachycardia
Tx: Thionamide, Iodine (to shutdown production of thyroid hormone via Wolf-Cahikoff effect), Bile-acid binders (to remove thyroid hormone from enterohepatic circulation), Nutrition (to heal), and Glucocorticoids (delays conversion of T4 to T3). Do not go to surgery
What is apathetic hyperthyroidism?
Thyrotoxicosis occurring in older adults in whom co-mordibities and aging may mask the features
How is hyperthyroidism diagnosed?
After H&E make sure to get a serum TSH (this is the most important because its level typically decreases the earliest in disease progression). Serum TSH should be low and the diagnosis can be confirmed with a high T4.
In a small subset of patients, hyperthyroidism can present as high levels of T3 (and thus low T4 levels and TSH levels)
After confirming the diagnosis, radioactive iodine uptake can be measured to find the source of the defect