IC14 Hyperthyroidism and Hypothyroidism Flashcards
What are the changes in Thyroid Function tests (T3, T4, TSH) in Hypothyroidism and Hyperthyroidism?
Changes in Thyroid Function tests (T3, T4, TSH) in Hypothyroidism and Hyperthyroidism
Hypothyroidism:
- Primary Hypothyroidism (e.g. Hashimoto)
o Low FT4
o High TSH - Central Hypothyroidism (hypothalamus / Pituitary gland is failing)
o Low FT4
o Low TSH
Primary Hyperthyroidism (thyroid gland functioning independently):
- High FT4
- Low TSH
Explain the physiology of thyroid gland and negative feedback mechanism.
Physiology of thyroid gland and negative feedback mechanism
- Influence development, growth and metabolism
- Increase oxygen consumptions + increase basal metabolic rate
o Body temp, CNS, sleep, cardiac function, GI functions, muscle strength, breathing, menstrual cycles, skin dryness, increase lipid metabolism, increase uptake and utilization of glucose
Regulation of TH levels:
- Negative feedback
a. Levels of TH will affect the levels of thyrotropin releasing hormone (TRH) from hypothalamus and TSH from pituitary - Peripheral conversion of T4 to T3
a. 80% of T3 are from T4
When does Thyronine binding globulin (TBG) change and how does the body react?
Thyronine binding globulin (TBG)
- When on estrogen / pregnancy –> TBG increases
- FT3 and FT4 decreases since more of them bind to TBG
- Body will be triggered and stimulate the thyroid gland to produce more FT3 and FT4
- FT3 and FT4 will then increase
How many tests needed to assess immunity for hyperthyroidism and hypothyroidism?
Test for autoimmunity:
Hashimoto hypothyroidism: 2 tests
Graves’ Disease: 3 tests (1 test is specific to Graves’ Disease, but expensive)
What are the current recommendations for screening of thyroid disorders? (8 in total)
- Have autoimmune disease
- 1st degree relative have thyroid disorders
- Psychiatric disorders (thyroid disorders could lead to mood swings etc., trying to find root cause)
- On some medications e.g. Amiodarone or Lithium
- History of head/neck radiation for malignancies
- Symptoms of hyperthyroidism or hypothyroidism
- Pediatric patients
- Pregnant patients
What are the different causes of hypothyroidism?
Different causes of hypothyroidism:
- Iodine deficiency
- Autoimmunity e.g. Hashimoto disease (especially in women)
- Iatrogenic (thyroid resection / RAI)
- Central hypothyroidism
- Drug-induced e.g. amiodarone, lithium
What are the signs and symptoms of hypothyroidism? (What are the complications of hypothyroidism - try answering)
Signs and symptoms of hypothyroidism
- Cold
- Dry skin
- Weight gain
- Coarse hair and nails
- Weak and tired
- Bradycardia
- Slow reflexes
- Periorbital swelling
- Menstrual disturbances (heavier and more frequent flow)
- Goiter
Complications:
- Increase total cholesterol, LDL-C, TG
- Increase atherosclerosis, MI risk
- Increase creatinine phosphokinase (CPK) levels
- Increase miscarriage risk
- Impaired fetal development
What are needed to diagnose hypothyroidism?
Diagnosis of hypothyroidism
- Signs and Symptoms
- Labs
a. Low T4 and high TSH (primary)
b. Low T4 and TSH (central hypothyroidism)
c. Positive antibodies (2 test)
What is the starting dose of levothyroxine for hypothyroidism? How do you titrate the dose?
Starting and maintenance dose
- Young, healthy adults: 1.5mcg/kg/day
- 50-60y/o AND NO CVD: 50mcg/day
- Have CVD: 25mcg/day
Titrate up or down by 25mcg/day
What are the ADRs of levothyroxine?
ADR
- Cardiac abnormalities e.g. tachyarrhythmias, angina, MI
- Fractures
- Hyperthyroidism
What are the counselling points for levothyroxine?
Counselling points
- Take 30-60mins before breakfast
OR 4 hours after dinner - Avoid Ca or Fe supplements, antacids or milk. If not, take 2hrs apart
What are the monitoring parameters and frequency for hypothyroidism on levothyroxine?
Monitoring parameters and frequency
Usually look at TSH (0.4-4)
Every 4-8 weeks when starting / change dose
Every 6 months-1 year once stable
If consistently increasing TSH and normal FT4, maybe non-adherence
If central hypothyroidism, check FT4 instead (since TSH will not respond)
When to use liothyronine?
Liothyronine:
- Not recommended
- Use when have myxedema coma
- If going for diagnostic therapy e.g. CT scan, can switch levothyroxine to liothyronine since shorter t1/2 and can just stop 1-2 days before it
- Use combi T3 and T4 when have normal TSH but still have hypo symptoms
What are risk of pregnancy and hypothyroidism? What can we do to reduce the risk?
Hypothyroidism with Pregnancy
- Many bad effects on pregnancy:
o Miscarriage
o Spontaneous abortion
o Congenital defects
o Impaired cognitive development - Will cause further drop in FT4 since mothers will provide fetus with THs for up to 6 weeks
- Need to increase dose
What is subclinical hypothyroidism?
What are the cut off points where there are high risk?
When to consider starting therapy for subclinical hypothyroidism?
Subclinical Hypothyroidism
- High TSH and normal FT4
- Sign of early Hashimoto disease
- If TSH > 7 –> Risk of heart failure
- If TSH > 10 –> coronary heart disease
- Consider treating –> 25-75 mcg/day
o If TSH > 10
o If TSH is 4.5-10 AND
Symptoms of hypothyroidism
TPO present
History of cardiovascular disease - If untreated, need to screen regularly for development of overt hypothyroidism
What are the possible causes of hyperthyroidism?
Causes:
- Graves’ disease
- Pituitary adenomas
- Toxic adenoma
- Toxic multi-nodular goiter
- Drugs induced (amiodarone, lithium)
- Subacute thyroiditis
What are the signs and symptoms of hyperthyroidism?
Signs and symptoms of hyperthyroidism
- Heat sensitive
- sweating
- Thin hair
- Goiter
- Bulging eyes
- Weight loss
- Tachycardia
- Nervousness, anxiety, insomnia
- Menstrual disturbances (lighter flow, more infrequent)
What are needed for the diagnosis of hyperthyroidism?
Diagnosis of hypothyroidism:
- Signs and symptoms
- Labs
a. Low TSH and High FT4 - Positive antibodies (3 tests)
- Radioactive iodine uptake
- Biopsy
When are oral medications used for hyperthyroidism?
Oral medications – Last line!
- Awaiting surgical resection or RAI
a. Minimizes risk of post-ablation hyperthyroidism due to thyroiditis - Those who can’t undergo RAI or surgery
- Mild disease
- Usually for women (since more responsive to treatment)
- Limited life expectancy
RAI ABSOLUTE CONTRAINDICATION with pregnancy
What are the symptoms of hyperthyroidism and pregnancy? What medications to give and when to give?
Patient Selection
Hyperthyroidism and Pregnancy:
Symptoms:
- Failure to gain weight
- Tachycardia
- Fetal loss if untreated (but thionamides have risk of embryopathy)
Give lowest dose, keep T4 at UNL
- 1st trimester: Give PTU (carbimazole will cause congenital malformations)
- 2nd and 3rd trimesters: Give carbimazole (PTU will cause hepatotoxicity and has lower potency)
What are the ADRs for thionamides (carbimazole, propylthiouracil)?
ADR
- Hepatotoxicity (for PTU)
- Rash, risk for SJS
- Agranulocytosis (usually within 3 months)
- Fever
What are the monitoring parameters and frequency for hyperthyroidism on thionamides?
Monitoring parameters and frequency:
Reach maximal effects at –> 4-6 months
TSH takes 1-2 years to return to norm (don’t look at this)
Monitor and make changes to dose –> every month (according to symptoms and FT4)
When to use non-selective beta blockers e.g. propranolol?
Patient Selection
- Symptomatic relief
- bridging therapy for those on thionamides and waiting surgery
- PRN for high risk patients e.g. elderly with CVD
- Thyroiditis
What are the ADRs for non-selective beta blockers e.g. propranolol
ADR
1. Hypotension
2. Bradycardia
When is iodides (Lugol’s solution) used? What are some things to take note of for Lugol’s solution?
Patient Selection
- Before surgery to shrink gland
- After RAI to inhibit post-ablation hyperthyroidism due to thyroiditis
- Thyroid storm
Take note of
- Effects only last for 7-10 days
- Do NOT use before RAI –> can reduce uptake of RAI into glands
What is subclinical hyperthyroidism and its risks? When is it compelling to start therapy?
Subclinical Hyperthyroidism:
- Low/undetectable TSH and normal FT4
- Risk:
- AF in patients > 60y/o
- Bone fracture in postmenopausal women
- Can start similar treatment to overt hyperthyroidism –> compelling when TSH < 0.1
- Start beta-blocker if have AF
- If untreated, screen regularly for development of overt hyperthyroidism
What are the medications that can induce thyroid disease?
Drug induced thyroid disease:
- Amiodarone
a. Have iodine
b. Can cause both - Lithium
a. Inhibit TH secretion and release –> increase TSH –> goiter and hypothyroidism
b. Thyroiditis (hyper)
