Hypothyroidism resident survival guide
|Hypothyroidism Resident Survival Guide Microchapters|
Synonyms and Keywords: Approach to hypothyroidism, Hypothyroidism work-up, Hypothyroidism management
Hypothyroidism is a clinical state where there is a reduced production or action of thyroid hormones - Thyroxine (T4) and Triiodothyronine (T3). It is classified based on the location of pathology into primary hypothyroidism, secondary hypothyroidism and tertiary hypothyroidism. The most common cause worldwide is Iodine deficiency. In iodine sufficient areas the most common cause is autoimmune thyroiditis. Risk factors for the development of hypothyroidism include female sex, iodine deficiency, selenium deficiency, presence of other autoimmune conditions. Clinical presentation depends on the degree and rapidity of hormone depletion. Patients can be asymptomatic or present with symptoms like cold intolerance, fatigue, weight gain, constipation, depression, neck mass. The diagnosis of hypothyroidism is made with the help of biochemical tests measuring TSH and Thyroxine (FT4) levels. Treatment of this condition is with Levothyroxine supplementation. 
Life Threatening Causes
- Primary hypothyroidism:
- Central hypothyroidism:
- Congenital hypothyroidism:
|Causes of hypothyroidism|
|Primary hypothyroidism||Central hypothyroidism
( Secondary and Tertiary )
|Autoimmune||Drug induced||Iatrogenic||Transient Hypothyroidism||Infiltrative disorders||Genetic causes||Iatrogenic||Tumors||Vascular||Infiltrative||Infectious||Miscellaneous|
|Signs and Symptoms of hypothyroidism are present.|
|TSH, free T4 (FT4)|
|TSH >5.5mU/L||TSH 0.5-5mU/L||TSH<0.5mU/L|
|FT4 Low||FT4 Normal||FT4 Elevated||FT4 Low||FT4 Low|
(Thyroid peroxidase antibody)
|Subclinical hypothyroidism||1. T4 to T3 conversion defect|
(5' deiodinase deficiency, amiodarone use),
2. Thyroid hormone resistance
|1. Central hypothyroidism, |
2. T3 replacement therapy
|1. Following excess levothyroxine withdrawal,|
2. "Post hyperthyroid" hypothyroidism
( I131 or surgery),
3. T3 replacement therapy,
|Autoimmune thyroid disease |
|1. Euthyroid sick syndrome |
2. External radiation
3. Drug induced
4. Iodine deficiency
5. Congenital hypothyroidism
6. Seronegative autoimmune thyroid disease
|Pituitary or Hypothlamus lesion||Congenital TRH, TSH deficiency, |
|TSH > 5.5mU/L, |
|TSH = 5.5 - 10 mU/L, |
|Start Levothyroxine||Symptoms of hypothyroidism|
|Measure TSH after 4-6 weeks||Present||Absent|
|Goal TSH = 0.4-4mU/L |
Adjust levothyroxine dose if goal TSH not reached
|Levothyroxine trial for 3-6 months.||TPoAB |
(Thyroid Peroxidase) Antibodies
|Symptoms of hypothyroidism||Positive||Negative|
|Resolved||Unresolved||Follow up with annual TSH||Follow up with TSH every 3 years|
|Lifelong levothyroxine therapy|
0r 0.5-5.5mu/L, FT4 Low
|MRI Brain||Give glucocorticoids for 1-2 weeks to prevent adrenal crisis|
|Reassess by measuring FT4 |
Goal FT4 is
upper limit of normal
- When to take Levothyroxine: Morning 30-60 minutes before breakfast or 4 hours after last meal of the day. To be taken at the same time each day with water.
- After initiation or change in dose of Levothyroxine in a patient diagnosed with hypothyroidism, serum TSH measurements should be done after 4-8 weeks. Once the target TSH level is reached, the TSH level is to be repeated after 6 months, thereafter every 12 months.
- In patients who are started on drugs that alter the absorption or metabolism of Levothyroxine, TSH should be measured within 4-8 weeks for dose adjustments.
- A patient may resume using the previously used full replacement dose of Levothyroxine after an interruption lasting less than 6 weeks if there was no cardiac event or weight loss in the interim.
- In a patient with subclinical hypothyroidism with TSH levels between the upper limit of normal and 10mIU/L treatment should be considered if -
- In patients with central hypothyroidism associated with adrenal insufficiency, glucocorticoid therapy should be given prior to starting Levothyroxine.
- In patients with central hypothyroidism FT4 levels guide therapy - target level should be greater than mid-normal range value.
- Serum FT3 or Total T3 levels – NOT to be used to diagnose hypothyroidism.
- In hospitalized patients, TSH measurements should not be done to assess thyroid function unless there is a high index of suspicion for thyroid disease.
- Cholesterol levels, muscle enzymes, reflex relaxation time - cannot be used as diagnostic tools for hypothyroidism.
- Thyroid replacement therapy NOT to be prescribed without biochemical evidence of hypothyroidism.
- Do not use thyroid replacement therapy for weight loss in obesity if the patient is euthyroid.
- Iodine supplementation/ iodine-rich foods should not be used in iodine-sufficient areas for hypothyroidism.
- Do not use Selenium for preventing or treating hypothyroidism.
- Do not use desiccated thyroid hormone for the treatment of hypothyroidism.
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