Thyroid CIS Flashcards
Thyroid hormone in growth and development (what is a nutritional deficit that leads to thyroid deficiency, and what are the consequences?)
Endemic iodine deficiency leads to cretinism
Mental retardation- permanent if hormone replacement is not started within days of birth
Growth delay leads to dwarfism which can be partially corrected
What is the most valid and useful assessment of thyroid function?
Serum TSH
Thyroid function tests
Serum thyroxine (total T4): normal 4-12 μg/dl - Total Serum T4 is influenced not only by the amount of hormone but also the amount of TBG
Free T4: normal 0.58-1.64 ng/dl
- Low levels and difficult to measure accurately
Triiodothyroxine (T3) levels: normal 90-190 ng/dl
Serum TSH: normal 0.5-5.0 μU/ml
- The most valid and useful assessment of thyroid function
What do we see (lab values) in hyperthyroidism?
decreased TSH and increased T4
often thyrotoxicosis
Hyperthyroidism examples
- Grave’s disease- autoimmune thyroid disease (0.5% of population) (Immunoglobulins act like TSH)
- Factitious thyrotoxicosis- exogenous thyroid hormone with gland atrophy and low thyroglobulin (over-replacement of thyroid hormone)
- Toxic adenoma “hot nodule”- overproduction of thyroid hormone by the nodule with low TSH and gland atrophy surrounding the nodule
- Toxic nodular goiter (toxic multinodular goiter)
- Subacute thyroiditis (granulomatous) (viral in etiology) with painful gland
Hyperthyroidism→ euthyroidism→ hypothyroidism→ euthyroidism (transient) - Silent thyroiditis (subacute lymphocytic) (believed to be autoimmune in etiology) with non-tender gland- transient
Example is postpartum thyroiditis - Pituitary overproduction of TSH- rare
Distribution of radioactive iodine
most useful for determining hyperthyroidism– you see a dramatic increase in thyroid levels of radioactive iodine. Uptake patterns can be useful in determining between different causes.
Graves Disease
Hyperthyroid→ most common cause is Grave’s Disease: occurs more commonly in women age 20-40
Triad of clinical finding:
- Hyperthyroidism- hyperfunctional, diffuse enlargement of the thyroid gland, TSH ↓ but T3, T4 and thyroid size ↑
- Infiltrative ophthalmopathy with exophthalmos
- Localized, infiltrative dermopathy (pretibial myxedema)
Autoantibodies are directed against the TSH receptor (activating) (thyroid-stimulating antibodies- TSAb or TSI)
Eye changes
- Volume of retro-orbital connective tissue and extraocular muscles is increased due to inflammation
Treatment: immune suppression, antibody clearance, blocking thyroid function, or gland removal
Hypothyroidism: points of interruption
Thyroid gland- primary
Pituitary- secondary
Hypothalamus- tertiary
Tissue resistance- rare
Primary hypothyroidism
Hashimoto’s (5-10% of population)- T cell-mediated but antibodies can also be present (α-TPO)
Radioactive ablation of the thyroid
Secondary hypothyroidism
pituitary insufficiency
Tertiary hypothyroidism
hypothalamic disease
Hashimoto’s Thyroiditis
- Inflammation of the thyroid gland
-More common in women (age 45-65) 10:1 to 20:1
Clusters in families - Hashimoto’s thyroiditis- Most common disorder of hypothyroidism in iodine sufficient areas
- T-cell-mediated with presence of autoantibodies: Autoantibodies against thyroglobulin and thyroid peroxidase, TSH receptor, and iodine transporter
- Gradual thyroid failure
- Classical presentation: goiter, skin change, peripheral edema, constipation, headache, fatigue, and anovulation
- TSH and TRH increase but T3 and T4 go down
Treatment: replacement therapy with levothyroxine (T4)
8 steps of Thyroid hormone synthesis
- Tgb synthesis on RER
- Iodine pumped in
- send to the lumen
- iodination
- coupling of Tgb with T4
- Endocytosis
- Tgb sent out into the blood with T4 and T3
- recycling of TG and iodide
some signs of hyperthyroidism
diarrhea, tremors, shorter menstrual cycles (turnover of proteins is quicker), medications might no longer be as effective because of increased degradation
what are dry skin and delayed deep tendon reflexes indicative of?
hypothyroidism
