Thyroid Flashcards
(44 cards)
What are follicles lined by?
cuboidal to low columnar follicular cells
What do parafollicular or C cells secrete? What origin ar they?
calcitonin-promotes absorption of calcium by the skeletal system and inhibits reabsorption of bone
Neural crest origin
What is the mechanism of action and function of thyroid hormones?
- Stimulation of protein synthesis
- Up regulation of carbohydrates and lipid catabolism
- Increase in basal metabolic rate
- critical role in the development of brain in fetuses and neonates
Thyrotoxicosis
Hyper metabolic state due to increased circulating levels of thyroid hormones (T4 and T3)
-most commonly caused by hyper functioning of the thyroid gland but can be not associated with hyperthyroidism
Clinical manifestations of hyperthyroidism/ thyrotoxicosis
Excess thyroid hormone and over activity of sympathetic nervous system
- Increased BMR-soft warm flushed skin
- Heat intolerance and excess sweating
- Weight loss despite increased appetite
- Cardiovascular-increased CO, tachy, palpitaitons, cardiomegaly, arrhythmias especially atrial fibrillation is common in the elderly
- Development of low output heart failure
- Neuromuscular-nervousness, emotional lability, insomnia, muscular weakness, fine tremor of the hands
- proximal muscle weakness and decreased muscle mass
- Gastrointestinal: hypermotility, malabsorption
- Wide staring gaze and lid lag
- Thyroid ophthalmopathy (proptosis) only associated with graves
- Stimulates bone resorption and osteoporosis
- THyroid storm-medical emergency
Diagnosis of hyperthyroidism
TSH levels-usually decreased-Most sensitive
Free T4-usually increased
How do you exclude secondary or pituitary associated hyperthyroidism?
TRH stimulation test
- inject TRH
- if normal rise in TSH then it is not secondary hyperthyroidism
What radioactive iodine uptake results indicate Graves, toxic adenoma, or thyroiditis?
graves: diffuse uptake
toxic adenoma: localized
thyroiditis: reduced uptake
What is the most common cause of hypothyroidism?
primary hypothyroidism
-can be accompanied by enlargement of the gland(goiter)
What is the most common worldwide congenital hypothyroidism due to?
iodine deficiency
Cretinism
Hypothyroidism in infants or early childhood
- secondary to iodine deficiency or rarely from inborn errors in metabolism
- impaired development of skeletal muscles and CNS: severity varies to timing of deficiency
- if maternal thyroid hormone deficiency before development of fetal thyroid, mental retardation is sever
- mental retardation, short stature, coarse facial features
Hypothyroidism Myxedema
Adult hypothyroidism
Gradual slowing of mental and physical activity
-fatigue, lethargy, apathy, slowed speech
-cold intolerance and reduced sweating
-overweight and constipation
-periorbital edema, thick coarse skin, enlarged tongue (deposition of glycosaminoglycans)
-reduced cardiac output causes shortness of breath and decreased exercise capacity
-promotes an atherogenic profile (increased cholesterol)-adverse cardiovascular mortalities
What lab values do you find in hypothyroidism?
Decreased T4
TSH levels-most sensitive for hypothyroidism
Primary-Increased TSH
Secondary-Decreased/normal TSH
Thyroiditis
types with Pain and No pain
- Inflammation with pain, sometimes severe
- Infectious thyroiditis
- subacute granulomatous thyroiditis (De quervain thyroiditis) - Relatively little pain
- Subacute lymphocytic thyroiditis
- Riedel’s thyroiditis
- Hashimoto’s thyroiditis
Hashimoto Thyroiditis
most common hypothyroidism in non-iodine deficient areas
- autoimmune destruction of thyroid gland
- 45-65
- major cause of non endemic goiter in pediatric age group
- strong genetic component
What are the three mechanisms of breakdown in self tolerance and induction of thyroid autoimmunity in Hash?
- T cell mediated cytotoxicity-CD8
- Thyrocyte injury-CD4-INF gamma-macrophages
- Antibody-dependent cell mediated cytotoxicity
What antibodies are seen in hashimoto thyroiditis?
- Thyroglobulin and thyroid peroxidase (TPO)!!!
- TSH receptor
- Iodine receptor
Hashimoto thyroiditis
Gross
Histology
Gross Diffusely enlarged gland Intact Capsule Well demarcated Pale, yellow, tan and somewhat nodular and firm
Histology:
- Thyroid follicles lined by Hurthle cells/oncocytes
- have abundant granular pink cytoplasm (numerous mitochondria) - formation of germinal centers
- Thyroid parenchyma infiltrated by mononuclear inflammatory cells
- blue lymphocytes
- pink cells forming a follicle with colloid in the middle-residual follicular cells
Clinical course Hashimoto Thyroiditis
- transient hyperthyroidism due to disruption of thyroid follicles with release of thyroid hormones (hashitoxicosis)
- gradual hypothyroidism
- increased risk of developing other autoimmune
- increased risk of developing Non Hodgkin B cell lymphoma
Subacute/Granulomatous (de quervain) thyroiditis
40-50 years of age
- viral or post-viral inflammatory response
- viral antigens or virus induced host tissue damage stimulates formation of cytotoxic T cells which then damage the thyroid follicular cells (process is self limited)
- Most Common cause of thyroid pain
- variable enlargement of thyroid
- history of upper respiratory infection
- transient hyperthyroidism–hypothyroidism–euthyroid
- hyperthyroid phase: T3, T4, decreased TSH, radioactive iodine is diminished
- recovery and normal thyroid function in 6-8 weeks
Subacute/Granulomatous (de quervain) thyroiditis
histology
- unilateral or bilateral enlarged firm with intact capsule
- changes are patchy
3.
early stage-disruption of follicles with collections of neutrophils forming microabscesses
later stage-aggregates of lymphocytes, plasma cells and activated macrophages around damaged thyroid follicles
-multinucleated giant cells of enclosed fragments of colloid - eventually chronic inflammation and fibrosis
Riedel thyroiditis
rare disorder of unknown etiology
- extensive fibrosis involving the thyroid and contiguous neck structures
- hard and fixed mass-clinically simulating cancer**
- may be associated with idiopathic fibrosis at other sites like retroperitoneum
- presence of circulating antibodies- autoimmune etiology
Graves Disease
Most common cause of hyperthyroidism
- Hyperthyroidism due to diffuse hyperfunctional enlargement of thyroid
- infiltrative opthalmo exophthalmo-accumulation of loose connective tissue behind eyeballs-weak extraocular muscles
- infiltrative dermopathy pretibial myxedema (present in minority of patients)
- 20-40 yrs
- 30-40% concordance in monozygotic twins as compared to 5% in di
What are the autoantibodies seen in graves disease
- Thyroid stimulating immunoglobulin (TSI)-binds to TSH receptor and mimics its actions (specific for graves)
- Thyroid growth stimulating immunoglobulin-cause(TGI) proliferation of follicular epithelium
- TSH-binding inhibitor immunoglobulin (TBII)