Hypothyroidism
For patient information click here
Hypothyroidism Main page |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]
Synonyms and keywords: Myxedema; myxoedema; thyroid activity decreased; hypothyroid
Overview
Environmental iodine deficiency is the most common cause of hypothyroidism on a worldwide basis (16). In areas of iodine sufficiency, such as the United States, the most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto’s thyroiditis).Autoimmune thyroid diseases (AITDs) have been estimated to be 5-10 times more common in women than in men.
Symptom and signs of hypothyroidism is mostly related to the magnitude of the thyroid hormone deficiency, and the acuteness with which the deficiency develops rather than the cause of hypothyroidism. However, the typical clinical manifestations of hypothyroidism may vary depending on the origin of the disease. Patient clinical manifestations- if associated with secondary and tertiary hypothyroidism, may present other coexisting endocrine deficiencies such as hypogonadism and adrenal insufficiency, that may mask the manifestations of hypothyroidism. Although hypothyroidism diagnosis is mainly a laboratory diagnosis, the coexisting conditions and wide variation in clinical presentation may make the diagnosis harder.
Classification
The table below presents a classification of isolated thyroid disorders and its causes based on the classification:
Origin of the defect | Causes | ||||||
---|---|---|---|---|---|---|---|
Endagenous causes | Exagenous causes | ||||||
Thyroid | Pituirtary | Hypothalamus | Surgery or radiation | Other causes | |||
Primary hypothyroidism | + | - | - |
|
|
| |
Transient hypothyroidism | + | + | - |
|
|||
Central Hypothyroidism | Secondary
OR Pituitary originated |
- | + | - |
|
|
|
Tertiary
OR Hypothalamus originated |
- | - | + |
|
|
|
Classification of thyroiditis based on the duration algorythm
History, signs, and symptoms suggestive of hypothyroidism | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Measure FT4 and TSH | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Normal FT4, Elevated TSH>5.5 | Decresased level of FT4 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Subclinical hypothyroidism | Elevated TSH > 5.5 | Normal TSH level OR Decreased TSH level < 0.2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Check anti-thyroid autoantibodies and TPOAb | Check TRH | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Increased | Normal | Normal or increased | Decreased | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
•Autoimmune thyroiditis • Resistance to TSH | •Iodine deficeincy •Thyroiditis | •Pituitary related hypothyroidism | •Hypothalamus related hypothyroidism | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Differential diagnosis
Disease | History and symptoms | Laboratory findings | Additional findings | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Fever | Goiter | Pain | TSH | Free T4 | T3 | T3RU | Thyroglobin | TRH | TPOAb | |||
Primary hypothyroidism | Autoimmune | + | +/-
Diffuse |
- | ↑ | ↓ | N/↓ | Normal | N/↑ | Normal | ↑ |
|
Thyroiditis | + | +/- | + | ↑ | ↓ | Normal | Normal | N/↑ | Normal | Normal |
| |
Others | - | +/- | - | ↑ | ↓ | Normal | Normal | N/↑ | Normal | Normal |
| |
Transient hypothyroidism | +/- | - | +/- | ↑ | ↑ | Normal | Normal | ↑ | Normal | Normal |
| |
Subclinical hypothyroidism | - | - | - | ↑ | Normal | Normal | Normal | ↑ | Normal | N/↑ |
| |
Central Hypothyroidism | Pituitary | + | - | - | N/↓ | N/↓ | N/↓ | ↓ | Normal | Normal | Normal |
|
Hypothalamus | + | - | - | ↑ | Normal | ↓ | Normal |
| ||||
Resistance to TSH/TRH | - | - | - | ↑ | N/↓ | N/↓ | Normal | Normal | ↑/↓ | Normal |
|
History and symptoms
Symptoms | Constituitional | HEENT | Neuromuscular | Complications |
---|---|---|---|---|
More common |
|
|
| |
Less common |
|
|
|