Thyroid Hormone Disorders: Tests, Symptoms, and Conditions

What is the normal feedback loop for thyroid hormones?

Hypothalamus -> TRH -> Pituitary -> TSH -> Thyroid -> T3/T4

What happens to TRH and TSH levels when T3/T4 are high?

They decrease due to negative feedback.

What is a primary disorder in thyroid hormone regulation?

A problem in the thyroid.

What does a high TSH level indicate?

Primary hypothyroidism.

What does a low TSH level indicate?

Primary hyperthyroidism.

What is the purpose of the Total T4 test?

To evaluate abnormal TSH levels; affected by serum proteins.

What does a high Total T4 level indicate?

Most hyperthyroid patients.

What is the significance of Free T4 (fT4) testing?

It evaluates abnormal TSH and is not affected by serum protein changes.

What does an elevated Reverse T3 (rT3) indicate?

Euthyroid sick syndrome.

What is the significance of TSI/Anti-TRAb testing?

It tests for autoantibodies present in Graves disease.

What are common symptoms of congenital hypothyroidism (cretinism)?

Lethargy, prolonged jaundice, feeding difficulty, mental delay.

What is myxedema associated with?

Severe hypothyroidism with symptoms like thickened skin and weight gain.

What lab findings are typical for primary hyperthyroidism?

TSH down, T3/T4 up.

What are the common findings in Graves disease?

Hyperthyroid symptoms plus exophthalmos and goiter.

What is the typical lab result for primary hypothyroidism?

TSH up, fT4 down.

What symptoms are associated with Hashimoto thyroiditis?

Hypothyroid symptoms; rubbery goiter.

What is the testing order for thyroid disorders?

1. TSH -> 2. T4/free T4 -> 3. Antibody testing.

What is the purpose of potassium iodide in nuclear exposure?

To saturate the thyroid iodine-uptake system and reduce radioactive iodine uptake.

What does a high TSH and low T4 indicate?

Primary hypothyroidism.

What are the key symptoms of Graves disease?

Weight loss, anxiety, tremor, exophthalmos, tachycardia.

What lab results indicate secondary hypothyroidism?

TSH down, T4 down.

What is the significance of subclinical hypothyroidism?

TSH high, T4 normal; T4 still normal.

What is the expected lab result for euthyroid sick syndrome?

Normal TSH, low T3/T4, rT3 increased.

What is the key antibody to look for in Graves disease?

TSI (Thyroid Stimulating Immunoglobulin).

What is a thyroid storm?

A life-threatening condition characterized by restlessness, delirium, psychosis, fever, marked tachycardia, and gastrointestinal/hepatic involvement.

What does the Burch-Wartofsky scale indicate?

It assesses the likelihood of thyroid storm:

What is Hashimoto's Thyroiditis also known as?

Chronic lymphocytic thyroiditis.

How does Hashimoto's Thyroiditis affect thyroid function?

Autoimmune lymphocytic infiltration damages thyroid cells, decreasing T3/T4 production.

What are the key autoantibodies associated with Hashimoto's Thyroiditis?

Anti-TPO (present in about 90%) and Anti-Tg (present in about 60-80%).

What is the expected lab pattern for primary hypothyroidism?

Increased TSH and decreased free T4 (fT4).

What are common symptoms of hypothyroidism?

Weight gain, fatigue, cold intolerance, hair loss, dry skin, constipation, bradycardia, and edema.

What causes toxic adenoma and toxic multinodular goiter?

Autonomous production of T3/T4.

What is Euthyroid Sick Syndrome?

A condition where the thyroid functions normally, but serious non-thyroid illness produces abnormal thyroid test results.

What is the lab pattern for Euthyroid Sick Syndrome?

Decreased T3 and T4, increased reverse T3, and normal TSH.

What does a high TSH and low fT4 indicate?

Primary hypothyroidism.

What does a low TSH and high T4 indicate?

Primary hyperthyroidism.

What is the role of TSH in thyroid hormone measurement?

TSH is the first-line thyroid test used to assess thyroid function.

What is the significance of thyroglobulin in thyroid cancer?

It is used to detect recurrence of differentiated thyroid carcinoma, such as papillary and follicular types.

What is the association of calcitonin in thyroid cancer?

Elevated levels are associated with medullary thyroid carcinoma.

What are the symptoms of myxedema?

Severe hypothyroidism symptoms including thick skin, hoarse speech, and weight gain.

What is the effect of pregnancy on thyroid hormone levels?

Increased estrogen raises TBG, leading to increased protein-bound/total T3 and T4, while free T3/free T4 and TSH remain normal.

What medications can cause hypothyroidism?

Lithium inhibits thyroxine release, and amiodarone has variable effects depending on iodine availability.

What is the relationship between TSH and T4 in primary thyroid diseases?

In primary disease, TSH and T4 move in opposite directions; in secondary disease, they move in the same direction.

What are the key characteristics of Graves' disease?

Autoimmune hyperthyroidism with TSI as the key antibody.

What are the distinguishing features of hyperthyroidism?

Symptoms include being hot, fast, thin, and anxious.

What are the distinguishing features of hypothyroidism?

Symptoms include being cold, slow, tired, and experiencing weight gain.