Hypothyroid

Loss of thyroid tissue leads to a decreased production of TH

Causes include

Autoimmune thyroiditis (Hashimoto disease)

Most common cause in United States

Gradual inflammatory destruction of thyroid tissue due to infiltration of

Lymphocytes

Circulating thyroid autoantibodies

Auto reactive T lympocytes

Antibody activation of natural killer cells

Induction of apoptosis

Due to genetic disposition

associated with

High iodine intake

Selenium deficinecy

smoking

chronic hepatitis C

IFN-A

Iatrogenic loss of thyroid tissue after surgical or radioactive treatment for hyperthroidism

Head and neck radiation therapy

Medications

Endemic iodine deficiency

Endemic goiter

Most common cause worldwide

Rare in U.S due to iodized salt and fortified foods

Lack of TH negative feedback on pituitary TSH secretion and hypothalamic TRH secretion

Low levels of TH and high levels of TSH and TRH

Infants and children with hypothyroidism

Caused by congenital defects

Pituitary or thyroid gland

Treatment

Hormone replacement therapy

Levothyroxine

Treatment of other symptpoms

Central (secondary) hypothyroidism

less common

Pituitary or hypothalamic failure with failure to stimulate normal thyroid function

Inadequate amounts of TSH or lack of TRH

Lack of negative feedback to hypothalamic release of TRH by TSH and TH

Low levels of TSH and TH and high levels of TRH

Caused by pituitary tumors that compress surround pituitary cells

Also caused by treatment of theses tumors

Traumatic brain injury

Subarachnoid Hemorrhage

Pituitary infarction

Sub-clinical hypothyrodism

4-8% of cases

Mild thyroid failure

Is an elevation in TSH level with normal levels of TH

Congenital Hypothyroid

Deficiency present at birth

Absent thyroid tissue

Hereditary defects in TH synthesis

Present in 1 of every 3 to 4 thousand births

Thyroid Carcinoma

Most common endocrine malignancy

Accounts for 60,220 cases a year with 1850 deaths

Ionizing radiation is most consistent causal factor

Infant mentally retarded due to absence of TH stimulating brain tissue, due to the vast number of manifestations, I inserted this chart