Endo: Thyroid Dysf Flashcards
Which is the active form of thyroid hormone: T3 or T4?
Does most T3/4 exist free or bound to protein?
T3 is more active
Most T3/4 exists bound to protein
Name 2 causes of increased total T4/3
Name 2 causes of decreased total T4/3
- Increased total T3/4
- Hyperthyroidism
- Increased binding proteins due to estrogen (OCP, pregnancy)
- Decreased total T3/4
- Hypothyroidism
- Decreased binding proteins due to renal or liver disease
Name one cause of increased free T3/4
Name one cause of decreased free T3/4
- Increased free T3/4 = hyperthyroidism
- Decreased free T3/4 = hypothyroidism
What labs do we use to evaluate thyroid function? (3)
Which is most important?
- TSH - most important
- Free T4
- Antibodies
Describe the results of a T3 Resin Uptake test
(assuming normal TBG levels)
- When TBG is normal, amount of radiolabeled T3 taken up is indicative of TBG saturation
- High T3RU (a lot of radiolabeled T3 left on resin) indicates hyperthyroidism
- Low T3RU (very little radiolabeled T3 left on resin) indicates hypothyroidism
What does it mean if Total T4 and T3RU go in opposite direction?
What about same direction?
- Opposite direction Total T4 and T3RU indicates an abnormality in the amount of TBG
- Same direction Total T4 and T3RU indicates a true thyroid hormone production problem
Symptoms of hyperthyroidism
- Temperature
- Weight
- Skin/Hair (2)
- Ocular (2)
- GI (2)
- MSK (1)
- Neuro
- CV (3)
Hyperthyroidism
- Heat intolerance
- Weight loss
- Skin/Hair: warm skin, onycholysis
- Ocular: exophthalmos (Grave’s), lid retraction
- GI: Increased defecation, increased appetite
- MSK: Osteoporosis
- Neuro: anxious, restless, insomnia, tremors
- CV: tachycardia, dyspnea, HTN
Compare overt and subclinical hyperthyroidism labs
- Overt
- low TSH
- Elevated T3/4
- Subclinical (can still have symptoms)
- low TSH
- T3/4 within normal
Define thyrotoxicosis
High level of T3/4 for any reason
What is the purpose of a iodine uptake scan?
Iodine uptake scans can be used together with a TSH level to determine whether the thyroid is responding appropriately to the TSH.
What is the use of thyroid uptake scans in patients with elevated T3/T4?
Thyroid uptake scan will differentiate hyperthyroidism from thyroiditis
- Hyperthyroidism: elevated or normal iodine uptake (despite suppressed TSH)
- Thyroiditis: low iodine uptake (appropriately responding to suppressed TSH)
Compare the overall cause of hyperthyroidism and thyroiditis.
Hyperthyroidism: Increased production of T3/4
Thyroiditis: Increased release of pre-formed T3/4 (due to inflammation or destruction)
*Both are forms of thyrotoxicosis (elevated T3/4)
Grave’s disease pathophys?
Grave’s Disease
- Auto-antibodies against TSH receptor (TSI-IgG) continually stimulates TSH receptor on thyroid
- Type II hypersensitivity
Tx of Hyperthyroidism (4)
- Thyroid hormone synthesis inhibitors, beta blockers
- Radioactive Iodine
- Targeted killing of thyroid gland
- Surgery
What is thyroiditis?
Explain its clinical course.
- Thyroiditis = inflammation of thyroid leading to increased release of pre-formed T3/4
- Timeline
- High T3/4, low TSH for a few months
- Once T3/4 stores are depleted, T3/4 is very low (thyroid is still sick and can’t produce hormones) and TSH becomes high
- Healing and return to normal occurs a few months later (self-limited)
Compare the labs of overt and subclinical hypothyroidism
- Overt
- Elevated TSH
- Low Free T4
- Subclinical
- Elevated TSH
- Free T4 is within normal
Symptoms of hypothyroidism
- Temp
- Weight
- Skin/hair (3)
- Ocular (1)
- GI (2)
- MSK (2)
- Neuro (2)
- CV (2)
Hypothyroidism
- Cold intolerant
- Weight gain
- Skin/hair: Hair loss, dry cold skin, generalized edema
- Ocular: periorbital edema
- GI: Constipation, decreased appetite
- MSK: carpal tunnel, myoedema
- Neuro: lethargic, depression, decreased reflexes
- CV: Bradicardia, exertional dyspnea
Compare the lipid profiles in hyper and hypothyroidism
Hypothyroidism: Hypercholesterolemia
Hyperthyroidism: decreased LDL, HDL, total cholesterol
Pathophysiology of Hashimoto’s Thyroiditis
- Auto-Ab’s against thyroid cause thyroid damage, leading to insufficient T3/4 production
- Ab’s against thyroid peroxidase or thyroglobulin
What is the treatment for hypothyroidism?
When do we initiate tx?
- Levothyroxine (synthetic T4)
- If TSH above 10
What is one thyroid emergency?
Myxedema coma: extreme form of hypothyroidism
Pt has bradycardia, hypothermia
Name 4 symptoms that occur in both hyper and hypothyroidism
- Fatigue
- Proximal weakness
- Menstrual changes and infertility
- Decreased libido
What is the most common cause of hyperthyroidism?
Grave’s disease
Grave’s disease is associated with what genotypes?
Grave’s disease = HLA-DR3 and HLA-B8
2 Unique symptoms of Grave’s disease
Why do these occur?
- Pretibial myxedema due to dermal fibroblast activation
- Exophthalmos due to T cell and fibroblast activation
What genotype is assocaited with Hashimoto’s thyroiditis?
HLA-DR3
Is the thyroid tender or non-tender in Hashimoto’s thyroiditis?
NON-tender
What is postpartum thyroiditis?
How does it present?
Histology?
- Self-limited thyroiditis following childbirth
- Hypo or hyperthyroidism with painless thyroid
- Histology: lymphocytic infiltrate
What is Reidel thyroiditis?
Is it associated with hyper or hypothyroidism?
Describe palpation of the thyroid
- Thyroid replaced by fibrous tissue with inflammatory cells
- Causes hypothyroidism
- Thyroid is a fixed, very hard, painless goiter
What is de Quervain thyroiditis?
Histology? (1)
Findings? (3)
- Self-limited hypothyroidism following viral infection
- Granulomatous inflammation
- Elevated ESR, jaw pain, painful thyroid (Quervain)
