Thyroid Disorders Flashcards
In the Hypothalamic-Pituitary Thyroid axis, the ____ secretes thyroid-releasing hormone (TRH)
Hypothalamus
The thyroid gland utilizes ______ & _____ to produce T3 & T4
Iodine & Thyroglobulin
Upon entering _____ , T3/T4 are cleaved via enzymes into a lipophilic structure
target tissues
Once T3 & T4 enter the blood stream they will ______ pituitary TSH secretion
INHIBIT
T3 & T4 are produced in what cells
Follicular Cell (responsible for
synthesizing & releasing)
Calcitonin is produced in what cells
Para-follicular cells
Solubility of T3 and T4 hormones
Lipid-Soluble
99% these hormones circulate within
the blood BOUND to thyroxine
binding globulin (TBG) and/or
albumin
* The unbound hormone, 1%, is
PHYSIOLOGICALLY ACTIVE
* T3 is more physiologically active
* T4 is changed in to T3
Solubility of Calcitonin
Peptide hormone (water soluble – travel
in the blood & binds on receptor
proteins)
FOUR main METABOLIC FUNCTIONS of T3/T4
- ↑ in Basal Metabolic Rate = ↑ ATP production by all cells in the
body, ↑ heat generation & O2 consumption. - ↑ CARDIAC OUTPUT = ↑ heart rate & contractility, ↑ blood pressure
- Stimulates BONE maturation & growth = ↑ RBC’s
- Increases metabolism (↑ gluconeogenesis, ↑ glycolysis, ↑ glucose
absorption, ↑ lipolysis, ↑ protein turnover)
* BRAIN = clear thinking, improved mood, & energy
Thyroid follicles are formed by thyroid epithelial cells surrounding _____ , which contains thyroglobulin.
proteinaceous colloid
Follicular cells, which are polarized, synthesize thyroglobulin & carry out
______
thyroid hormone biosynthesis
Subclinical hyper/hypo-thyroidism is
– Normal FT4 with ↑ or ↓TSH
– No physical symptoms
What is Euthyroid
Euthyroid
– Normal TSH
– Euthyroid sick syndrome
* ↓ T4 + symptoms
Secondary thyroidism refers to the _____
Pituitary
Hypothyroidism (Central Hypothyroidism) is
Insufficient stimulation of the thyroid gland by TSH (hypothalamic or pituitary disease)
Secondary hyperthyroidism involves what
TSH producing tumor
Hyperthyroidism Epidemiology
Prevalence
– 1.3%, more common in women than men at 5:1 ratio
– 4-5% in older women
– More common in smokers.
Primary vs. Secondary Hyperthyroidism Etiology
Primary
– Graves Disease (autoimmune)
– Subacute thyroiditis
* “DeQuervain” thyroiditis
– Cause = viral infection
– ↑ iodine intake
– ↑intake of exogenous thyroid
hormone
– Drugs (Amiodarone)
Secondary
– ↑ TSH
* Anterior pituitary
adenoma
– ↑ TRH secretion
* Hypothalamic tumor
An Autoimmune disorder of the thyroid gland, characterized by ↑ synthesis & release of thyroid hormones
Grave’s disease
Features of Graves Disease
Autoimmune disorder of the thyroid gland, characterized by ↑
synthesis & release of thyroid hormones.
* More common in women than men 8:1
* Onset 20-40 years
* Associated with ↑ antibodies, exophthalmos, pretibial myxedema,
onycholysis (separation of nail from its bed)
* ↑ risk other autoimmune disorders
Subjective (symptoms) and Objective findings (signs) in Hyperthyroidism
Subjective complaints (SYMPTOMS):
– Sweating, weight loss or gain, anxiety, palpitations, loose stools,
heat intolerance, irritability, fatigue, weakness, menstrual
irregularity.
- Objective Findings (Signs):
– Tachycardia; warm, moist skin; stare; tremor; exophthalmos -
(abnormal protrusion of the eyeball or eyeballs d/t retro-orbital
eye fat/infiltration)
exophthalmos is
abnormal protrusion of the eyeball or eyeballs d/t retro-orbital
eye fat/infiltration
Epidemiology of Hypothyroidism
Prevalence: >1% of population, >5% over 60 yo
Primary causes of Hypothyroidism
PRIMARY CAUSES
1. Failure of the thyroid gland
(95% of all cases)
* Autoimmune disease
* HASHIMOTOS THYROIDITIS
– MOST COMMON CAUSE
- Iodine deficiency/excess
- Drugs (Amiodarone, interferon)
- Iatrogenic
– Resection and/or
radioiodine therapy
Secondary causes of Hypothyroidism
- TSH deficiency
- TRH deficiency
– Mass lesions,
congenital/genetic
abnormalities/acquired
(concussions),
functions
(aging/anorexia)
HASHIMOTOS THYROIDITIS is the most common cause of what
Primary Hypothyroidism
What is HASHIMOTOS THYROIDITIS
Autoimmune disease
* Patients can frequently have other side effects due to co-occurring
autoimmune diseases:
* Eg// Addison disease, hypoparathyroidism, diabetes mellitus I,
pernicious anemia, sjorgen syndrome, vitiligo
* 5% have celiac disease
Subjective (symptoms) and Objective findings (signs) in Hypothyroidism
- Subjective complaints (SYMPTOMS):
– Weakness, fatigue, lethargy, arthralgia’s, cold intolerance,
constipation, weight gain, depression, menorrhagia, headache,
carpal tunnel syndrome, Raynaud’s syndrome. - Objective findings (SIGNS):
– Bradycardia; thin, brittle nails, thinning of hair; peripheral
edema, puffy face & eyelids, skin pallor or yellowing; delayed
deep tendon reflexes, palpably enlarged thyroid (GOITER),
hoarseness - Also known as: mild to severe MYXEDEMA
Severe Adult Hypothyroidism is also known as _____
Myxedema Crisis
* Swelling of the skin & underlying tissues
– Waxy consistency (firm & inelastic)
– Non-pitting edema,
– Dry skin & hair (frowzy hair)
– Dull apathetic appearance, swollen lips, thickened nose.
Myxedema Crisis is a ____ form of hypothyroidism
Life threatening
Impaired cognition → Confusion → Somnolence → Myxedema coma
Most common population for to get Myexedema Crisis
elderly women who have had a stroke or
stopped taking thyroxine medication
Characteristics of Hypo vs. Hyper thyroidism
Hypothyroidism
* Foggy thinking
* Depressed
* Low heart rate
* Low blood pressure
* Anemia → cold, pale, tired
* Low energy/fatigued
* Obesity (↓ use of fatty acids 2°↓ ATP)
Hyperthyroidism
* Agitated
* Irritable
* Rapid Heart rate/palpitations
* High blood pressure
* Polycythemia → hot, flushed, restless
* Restless
* Thinner
Characteristics of Euthyroid Sick Syndrome
Pt without known thyroid disease, with ↓ serum FT4 & normal TSH
1. Pregnancy
2. Major surgery
3. Chemotherapeutic agents
4. Viral thyroiditis
* Initial (typically) hyperthyroid state then → hypothyroid
- Critical illness
- Liver/renal disease
- Malnutrition
Laboratory tests for Thyroid Diagnostic testing
- Thyroid-stimulating hormone (TSH)
- Most sensitive test for primary hypo/hyper-thyroidism.
- SINGLE best screening test for HYPOthyroidism.
- Free Thyroxine (FT4) – commonly used along with TSH.
- Free Triiodothyronine (FT3) – more sensitive for hyperthyroidism
- Anti-thyroid antibodies
– Anti-thyroglobulin (Tg) Ab
– Anti-thyroid peroxidase (TPO) ab
SINGLE best screening test for HYPOthyroidism
Lab test for Thyroid-stimulating hormone (TSH)
You have low TSH and low serum T4/T3
Central Hypothyroidism
High TSH and Low T4/T3
Primary hypothyroidism
Low TSH and High T4/T3
Primary Hyperthyroidism
High TSH and High T4/T3
Secondary Hyperthyroidism
Imaging studies for Thyroid diagnostic testing
- Imaging is usually not needed in most cases of thyroid disease
- Ultrasound = Test of Choice (no radiation)
– Thyroid nodules - fluid vs. solid
- to guide biopsy
- Radioiodine scan – Confirm cancerous nodule or Graves dz
- Chest X-ray – Metastatic thyroid cancer to the lungs (typical)
- CT/MRI = (MRI preferred) Metastatic thyroid cancer throughout
the body
Additional Thyroid testing
- Fine-needle Aspiration (FNA)
Biopsy
– Best diagnostic method for
thyroid cancer - Thyroid uptake scan (131I)
– Cancers are usually found
as “cold” spots - 99mTc scan
– Evaluates nodule vascularity
– Ultrasonography
– Used to get FNA
– Helps assess malignancy
– Useful for nodule
monitoring
Management of Hypothyroidism
- Levothyroxine (Synthroid®)– Synthetic T4 – MOST COMMON
- Liothyronin (Cytomel®) – Synthetic T3
- Thyroid (porcine) (Armour Throid®) – Natural T3 & T4 mixture, 1:4 ratio
Instructions for levothyroxine (Synthroid®)
- Take in the AM, empty stomach with water (food ↓ absorption)
- Take 30 minutes before any food or other medications
- Food ↓ absorption (esp. grapefruit)
You should Retest TSH & T4 (or FT4) in _____ after medication initiation
6-8 weeks
Management of Hyperthyroidism
- Thiourea Meds
– Methimazole (Tapazole®): Inhibits thyroid hormone synthesis
– Propylthiouracil: Inhibits thyroid hormone synthesis - Propranolol ER (Inderal LA®) – Treat symptoms of tachycardia & anxiety
- Thyroid ablation – Radioactive Iodine (131I), Destroys thyroid tissue
- Thyroidectomy
