Thyroid disease Flashcards
What enzyme converts T4 to T3?
Type 1 or 2 Deiodinase
Type 3 deiodinase
Removes iodine from T3 and makes reverse T3 (inactive)
What types of things can inhibit Type 1 or 2 Deiodinase?
T4 cannot be converted to T3
- Starvation
- Severe illness
- Severe stress
- Neonatal period
Half life of T4 and T3
T4: 7 days
T3: 1 day
Causes of increase total T3 and T4
- Hyperthyroidism/Thyrotoxicosis
- Increased binding proteins
- Estrogen: acts on liver and stim TBG and albumin production - binds more T3 and T4 - Thyroid H resistance
Causes of decreased total T4 and T3
- Hypothyroidism
- Decreased serum protein binding
- Euthyroid sick syndrome
- Drugs
- Liver or kidney disease
TSH nl range
0.4-4.0
Thyroid hormone axis
D2, T4–>T3, at hypothalamus secretes TRH –>
Ant pit secretes TSH –>
Thyroid releases T3 + T4
TSH significance
- when is it elevated?
- when is it suppressed?
- Single best test to screen for thyroid dysfxn
- Indicates indiv. TH “set points”
- TSH stimulates Iodine uptake into thyroid follicular cells and TH production
Elevated: in primary HYPOthyroidism
Suppressed: in primary HYPERthyroidism
Sx of hyperthyroidism
- Nervousness
- Weight loss
- Increased appetite
- Fatigue
- Tremor
- Heat intolerance
other:
- Palpitations, hyperdefecation, trouble sleeping, diaphoresis
Which should you not order? TSH, Free T4, Free T3
Free T3
Thyrotoxicosis
- What
- TSH, free T4 + T3 levels
- Two causes
High circulating lvls of TH (various causes)
Serum TSH is low
Free T4 and total T3 are elevated
Overproduction of T4+T3: suggestive of hyperthyroidism
High release of PREFORMED T4 and T3:
no true hyperthyroidism
If TSH is suppressed, should the thyroid gland take up Radioactive iodine?
no - if it does, it indicates HYPER thyroidism
TSH is low: no stimulus to take up iodine
TSH fxn
stimulates the thyroid to take up iodine
and
synthesize T4 and T3
In thyrotoxicosis, should TSH be high or low?
Low: the hypothalamus and pit “sense” elevated T4 and T4 and secretion of TRH and TSH is suppressed
- if TSH is suppressed, there should be no uptake of iodine
A nl or elevated Iodine uptake in the setting of a LOW TSH indicates:
indicates autonomous production of thyroid hormone
- true hyperthyroid state
If the uptake of iodine is low in the setting of a low TSH (appropriately so), what could TH excess be due to?
High release of preformed TH
Low uptake Hyperthyroidism
- Subacute thyroiditis
- granulomatous thyroiditis (viral) - Chronic lymphocytic thyroiditis
- Radiation-induced thyroiditis
- Infectious thyroiditis
- Drug induced thyroiditis
- Ectopic thyrotoxicosis
High uptake hyperthyroidism
- Thyrotropin receptor antibody
- Graves - Thyroid autonomy
- toxic adenoma
- toxic multinodular goiter (MNG) - HCG
- TSH
Graves disease has ______ autoantibodies against the TSH receptor
Thyroid stimulating Immunoglobulin
–> causes high uptake Hyperthyroiditis
Common locations for Graves disease findings
Due to deposition of glycosaminoglycan behind eyes and in dermis over shins
- Opthalmopathy
- Pretibial Myxedema
Treatment for Graves disease
- drugs:
- Antithyroid H drugs: methimazole, propylthiouracil
- Beta blockers: reduce systemic hyperadrenergic symptoms and effects - Radioactive Iodine
- Surgery
How do you determine the cause of thyrotoxicosis if there is no true TH production?
If pt has thyroid autoimmune damage –> release a ton of preformed TH –>
Body senses and drops TSH levels –>
Body reaches thyrotoxic phase
- antithyroid drugs done work since it inhibits TH SYNTHESIS, (not the case here)
Eventually T4 levels fall –>
Body senses and increases TSH –>
Body cant make more T4 –> Hypothyroid phase
Symp of hypothyroidism
- mental slowness
- weight gain
- decreased appetite
- Fatigue a (non specific)
- muscle cramp
- cold intolerance
Etiology of hypothyroidism
- Chronic autoimmune (Hasimoto’s) thyroiditis
- Transient hypothyroidism
- Iatrogenic
- Pituitary tumor (secondary)
Hashimoto’s Thyroiditis
:
thyroid autoantibodies
- TPO (thyroid peroxidase)
2. Tg (thyroglobulin)
How to treat a pt with a TSH >10 mIU/L?
Nl TSH is 0.4-4.0
So treat with levothyroxine (synthetic T4) –> body (-) feedbacks and reduces TSH
