thyroid gland Flashcards
What happens if thyroid disorders are undetected or improperly treated?
They can result in long-term complications, including increased mortality.
incidence of hypothyroidism and hyperthyroidism?
Hypothyroidism (3.7% incidence).
Hyperthyroidism (0.5%)
thyroidsm relation with age and pregnancy?
- hypothyrodism incidence increase with age
- Pregnant women were also found to have higher prevalence of hypothyroidism.
What is the structure and hormone production of the thyroid gland?
The thyroid gland has two lobes in the lower neck and produces T4 (Tetra-iodothyronine) and T3 (Tri-iodothyronine).
Where are T4 and T3 produced and their ratio?
Both hormones are synthesized in follicular cells of the thyroid, with a secretion ratio of 10:1 (T4 to T3).
Q: What are the daily secretion levels of T4 and T3?
The thyroid secretes
80–100 μcg of T4
10 μcg of T3 daily.
Q: What are the half-lives of T4 and T3?
A: T4 has a plasma half-life of 6–7 days, and T3 has a shorter half-life of 24–36 hours.
How is T3 produced in the body?
10% of T3 is secreted by the thyroid, while 90% is produced by peripheral conversion of T4.
What causes primary hypothyroidism, and how common is it?
Primary hypothyroidism accounts for more than 95% of adult cases
- due to thyroid gland failure, often from autoimmune destruction (Hashimoto disease),
- treatment of thyrotoxicosis.
What causes secondary, tertiary, and peripheral hypothyroidism?
Secondary: Due to hypopituitarism.
Tertiary: Due to failure of the hypothalamus.
Peripheral: Due to tissue insensitivity to thyroid hormones.
Which drugs can induce hypothyroidism, and how common is it?
Amiodarone and lithium cause hypothyroidism in around 10% of treated patients.
Q: What are the symptoms of hypothyroidism, and why is it often misdiagnosed?
symptoms are non-specific, gradual in onset, and affect multiple body systems. Hypothyroidism is often confused with simple obesity and depression.
Therapy Goals.
- Minimize or eliminate symptoms; improve quality of life.
- Minimize long-term damage to organs (myxedema coma, heart disease).
- Normalize free T4 and TSH concentrations.
Initial dose of T4 will depend on the patient’s factors:
- Age.
- Severity.
- Duration of disease.
- Coexistence of cardiac disease.
replacement therapy for hypothyroidism
Levothyroxine (T4) is the treatment of choice for all patients with symptomatic hypothyroidism.
Exception: In cases of myxoedema coma, T3 (liothyronine) may be used initially. why?
Bcz its life threatning and t4 has to convert to t3 but we need fast action thts why we use t3
dose of young / healthy adult:
50-100 mcg
adult dose of t4
and
if pregnant thn which dose?
125mcg daily
1.6mcg/ibw kg
if pregnant: increase 25-50%
elderly dose of t4
25mcg/day thn increase by 25mcg every 4-6 weeks
cardiac patient dose
12.5- 25mcg/day
not check TSH earlier than 6 weeks why?
Do not check TSH earlier than 6 weeks, as it takes time for TSH to stabilize after a dose change.
Timing of Doses:
of t4
In the morning: 30–60 minutes before breakfast.
Or
at bedtime: 3–4 hours after the last meal.
Q: What is a drug holiday and why is it relevant in hypothyroidism treatment?
A drug holiday is the conscious decision to stop medication temporarily. In hypothyroidism, T4 requires lifelong treatment, but low adherence occurs when patients feel well and believe treatment is no longer necessary.
Q: What are the potential adverse effects of hypothyroidism medication?
- Hyperthyroidism
- cardiac abnormalities (e.g., tachyarrhythmias, angina, myocardial infarction)
- increased risk of fractures.
wht is bioequilance for levothyroxine can we change one brand to another
Although legal, guidelines recommend against changing from brand to generic and vice versa. It is recommended to stay with one product throughout therapy.
Q: What is myxoedema coma, and why is it significant?
Myxoedema coma is a rare but potentially fatal complication of severe, untreated hypothyroidism, classified as a medical emergency
What is the mortality rate associated with myxoedema coma?
The mortality rate is between 30% and 60%.
How should myxoedema coma be treated?
A: It should be treated rapidly and aggressively with intravenous thyroid hormone replacement, with some advocating for T3 over T4.
difference between Thyrotoxicosis and Thyroiditis
Thyrotoxicosis (increased hormone synthesis):
example: grave diease, plummer diease, Toxic single adenoma, Iodine induced.
Thyroiditis: thyroid destruction and leakage of stored thyroid hormones: Acute, Silent, Amiodarone induced.
Graves’ Disease.
Is the commonest cause of thyrotoxicosis.
It is an autoimmune condition, results from production of an abnormal IgG immunoglobulin
which can occupy the TSH receptor on the thyroid follicular cell.
Nodular disease
- Also known as Toxic multinodular goiter (Plummer disease).
- Several autonomous follicles that, if large enough, cause excessive thyroid hormone
secretion.
Thyroiditis
- Also called Painful subacute thyroiditis.
Thyroiditis is inflammation caused by viral infection or rapid autoimmune attack, leading to follicular cell death and release of pre-formed thyroid hormones. It is self-limiting, with a brief hyperthyroidism phase followed by subnormal hormone levels.
three forms of therpy for hyperthyroidism
anti thyroid drugs
surgery
radio active iodine
What are the challenges of using surgery and radioactive iodine in children and pregnant women?
children: surgery is complicated and and radioiodine is avoided due to the risk of thyroid malignancy.
pregnancy: Radioiodine is not used because it may cause hypothyroidism in the neonate. Surgery is deferred until the second trimester, and most patients are controlled with drugs.
What is ablative therapy, and when is it required?
A: Ablative therapy uses heat or cold to destroy tissue and is required for all patients with toxic multinodular goiters. It can be achieved through radioiodine or surgery.
Q: How does radioactive iodine therapy work, and who should avoid it?
A: Administered orally, radioactive iodine is absorbed into the bloodstream, concentrates in the thyroid, and destroys thyroid cells. It is contraindicated in pregnancy and breastfeeding.
wht is thyroid storm
Thyroid storm is a life-threatening condition caused by severe thyrotoxicosis.
thyroid storm sign and symptoms
high fever
Tachycardia (fast heart rate)
Tachypnea (fast breathing)
Dehydration
Delirium or coma
GI disturbances
g
Causes of thyroid storm (Triggers in hyperthyroid patients):
infection
Trauma
Surgery
Radioactive iodine (RAI) treatment
Sudden withdrawal of antithyroid drugs
Treatment for Thyroid Storm:
- beta block: IV esmolol
- iv or oral idoide
- large dose of PTU or mmi
- life support: paracetmol, fluid electrolyte,, antiarrythmic drug
- IV hydrocortisone (steroids): suppress adrenal insuffiency, Steroids also suppress serum T3 levels.
what is wolff chaikoff efect?
treats hyperthyroidism through a process known as the Wolff-Chaikoff effect.
* Wolff–Chaikoff is effective of rejecting a large quantity of imbibed iodide, and thereforepreventing the thyroid from synthesizing large quantities of thyroid hormone.
iodide used in?
- Graves disease before surgery 7-14 days prior used
- and to quickly reduce hormone release in patients with thyroid storm.
iodide effect last and work?
- Serum T4 levels may be reduced within 24 hours, and the effects may last for 2 - 3 weeks.
doses of iodide and dosage form
Potassium iodide is administered either as a
1. saturated solution(contains up to 50 mgiodide/drop) or as
2. Lugol’s solution (contains up to 8 mg iodide /drop)
starting dose of iodide
- The typical starting dose is 120 - 400 mg iodide/day.
most frequent toxic effects of iodide:
- hypersensitivity reactions,
- iodism (characterized by
palpitations, depression, weight loss & pustular skin eruptions), - gynecomastia.
- The thionamide agents use to treat hyperthyroidism
Propylthiouracil (PTU)
2. Methimazole (MMI)
3. Carbimazole (a prodrug for methimazole - available in some countries including
Bahrain)
when to check levels after thionmide treatmenr
hyroid function testing should be performed every 4 -to 6 weeks until stable.
* After initiating treatment, thyroid hormone levels drop within 2 - 3 weeks, and after 6 weeks, 90%
of patients with Graves disease become euthyroid.
thionamide drugs used in?
primary therapy for Graves disease or as preparative therapy before surgery or radioactive iodine.
intial dose hgh and reduce as test normal
se of antithyroid drugs and how to check and how to check severity
The major SE of antithyroid drugs is agranulocytosis, which should be monitored by CBC and
patients advised to seek medical help if severe mouth ulcers, sore throat or febrile illness occur.
Hyperthyroidism during Pregnancy
PTU is considered the treatment of choice, particularly in the 1st trimester. MMI is believed to have greater teratogenic potential, so should be avoided.
Given the potential maternal adverse effects of PTU (e.g. hepatotoxicity), it may be preferable to switch to MMI in the 2nd & 3rd trimesters.
MMI is preferred in nursing mothers because of
hepatotoxicity risk from PTU in the mother & infant.
Untreated maternal thyrotoxicosis may result in
miscarriage, premature
delivery, eclampsia, and low-birth-weight infants.
