HYPERTHYROIDISM Flashcards
what is the hypothalamic- pituitary-thyroid axis?
complex neuroendocrine web that determines the set point of thyroid hormone production
is the hypothalamic- pituitary-thyroid axis a positive or negative feedback loop?
negative feedback
is t3 or t4 more metabolically active?
t3
what are t3 and t4 derived from?
tyrosine
what is the definition of hyperthyroidism?
excessive thyroid hormones (t4 and t3) produced and released by the thyroid gland
what are the causes of hyperthyroidism?
- increased synthesis of thyroid hormones
- excessive passive release of thyroid hormones
- extrathyroidal source
- pituitary adenoma (secondary hyperthyroidism)
what is the epidemiology of hyperthyroidism?
females over males
20-40 years old is typical age of onset
what is the 2nd most common cause of hyperthyroidism in the USA (15% cases) ?
toxic multinodular goiter
what occurs in toxic multinodular goiter?
thyroid has multiple hyperfunctioning areas
what age population is toxic multinodular goiter most seen in?
elderly patients (>50 years)
what is a very common characteristic in most patients with toxic multinodular goiter?
smoking!
where is the highest incidence of toxic multinodular goiter seen in?
in iodine-deficient area
what is the most common cause of hyperthyroidism in the USA (60-80% of cases) ?
graves disease
what is graves disease?
autoimmune disorder in which antibodies against the thyroid stimulating hormones (TSH) receptors cause thyroid gland to hyperfunction (primary hyperthyroidism)
what happens to the thyroid in graves disease?
the thyroid develops diffuse hypertrophy and hyperplasia of the follicular cells with lymphoid infiltrates (toxic goiter)
what are risk factors for graves disease?
female
fmhx of thyroid disease
personal or fmhx of an autoimmune disease
under the age of 40
stress
smoking
what happens to the irregular follicles in hyperthyroidism?
they have decreased colloid (fluid within follicles that contains thyroglobulin)
what is a variable clinical presentation of hyperthyroidism?
asymptomatic —> thyroid storm
what are hyperthyroid symptoms ?
palpitations/tachycardia
heat intolerance/diaphoresis (vasodilation)
wt. loss d/t increased metabolic rate
EXOPTHALMOS/PREORBITAL EDEMA/excessive lacrimation
fine tremors and hyperreflexia
diarrhea
weakness of prox. muscles
psychosis/anxiety
GOITER
>graves- smooth, symmetric, non-tender w/ thrill or bruit on auscultation (d/t increased blood flow)
PRETIBIAL MYXEDEMA - swelling over tibia within skin assuming a peau d’ orange appearance
what will TSH show in graves and multinodular goiter?
low TSH
what overall labs will you see in hyperthyroidism?
- low TSH
- high T4 and T3
- increased thyrotropic receptor antibodies (graves)
what are the 2 other diagnostic testing options for hyperthyroidism that is not TSH lab values?
radioactive iodine uptake and thyroid scan
what does a higher uptake on a RAIU mean?
graves disease or toxic multinodular goiter
what is entailed in RAIU?
the uptake is a percentage of a radioactive iodine (i-123) tracer dose taken up by thyroid at 24 hours; it essentially helps to determine the cause of hyperthyroidism
what does a thyroid scan show?
the distribution of the radiotracer
what does homogenous distribution of the radiotracer indicate?
graves disease
what if there are multiple areas of accumulation on a thyroid scan?
Toxic multinodular goiter
what is the purpose of a dx thyroid ultrasound?
it detects diffuse enlargement, solitary or multiple nodules, and increased vascularity of the gland
what is the primary imaging modality used during pregnancy and lactation?
thyroid US
what management option is used to control adrenergic symptoms (palpitations, tremor, heat intolerance)?
beta blockers
what drug is very useful in impending thyroid storm?
beta blockers
what are the 2 beta blockers in order of most likely to use?
- propranolol
- atenolol
whats the difference between propranolol an atenolol?
propranolol: non-selective
- immediate release: 10-40 mg PO every 8 hours
- extended release: 80-160 mg PO once daily
atenolol: selective
- 25-100 mg PO once or twice daily
- safer for use in patients with asthma or COPD
what is the preferred treatment of graves disease along with dosage, and indications?
- methimazole 10-30 mg PO QD
- indicated in patients EXCEPT for 1st trimester of pregnancy; leads to birth defects
what does antithyroid medication do for graves?
two things that are pathophys
- inhibit oxidation and organic binding of thyroid iodine by inhibiting thyroid peroxidase
- inhibits extrathyroidal conversion of t4 to t3
what is required before initiating anti thyroid meds?
a baseline CBC and liver fxn (agranulocytosis)
what is the monitoring protocol for antithyroid hormone med therapy?
monitor free t4 and t3 obtainedd 4 weeks after initiation and every 4-8 weeks w/ dosage adjustments
what is another drug other than methimazole that can be used for graves as well as dose and indications?
- propylthiouracil 100 mg PO TID
- used in first trimester of pregnancy and in thyroid storm
- BLACK BOX WARNING- severe liver damage
overall, what are the 3 options of treating graves disease?
- antithyroid meds (2)
- radioactive iodine
- total thyroidectomy
what is the most common tx of graves in the US?
radioactive iodine (i-131) ablation of thyroid
how is radioactive iodine done?
there is a capsule or solution of sodium iodine that is taken orally (either i-131 or RAI)
i-131 concentrates in thyroid -> progressive thyroid cell destruction
is radioactive iodine contraindicated in pregnancy and breast feeding?
YES
what do most patients develop 2-6 months post radioactive iodine ablation?
permanent hypothyroidism requiring thyroid hormone replacement
in what patients is a total thyroidectomy preferred in?
patients w/ compressive symptoms and those w/ contraindications to radioactive iodine ablation or failure w/ antithyroid meds
what is a thyroid storm?
a rare life threatening emergency where there is more unbound thyroid hormone in the blood. Tissues might become more sensitive to the thyroid hormone, and body might become more sensitive to catecholamines activating the sympathetic nervous system
who does the thyroid storm occur in?
in patients previously undiagnosed or inadequately treated for hyperthyroidism
what are precipitating factors of thyroid storm?
- major stress (surgery, childbirth)
- trauma
- illness
- taking too much thyroid hormone
what is the clinical presentation of a thyroid storm?
fever, delirium, N/V, anxiety leading to seizures, cardiovascular manifestations: a fib w/ rapid ventricular response, hypotension
what is the management of thyroid storm?
six things
- supportive therapy- O2, airway maintenance
- anti-thyroid meds (methimazole)
- propranolol to control adrenergic symptoms
- oral or IV sodium iodide to decrease thyroid hormone release
- glucocorticoids to block the conversion of T4 to T3
- plasmapheresis
what is involved in plasmapheresis?
the blood plasma is removed, thyroid hormone can be removes, and remaining plasma is returned to patient
