Hypothyroidism resident survival guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Overview

Hypothyroidism refers to a clinical state where there is reduced production or action of the thyroid hormone.

Causes

Hypothyroidism can be classified based on the location of the pathology or based on etiology as shown in the table below.

Causes of hypothyroidism
Primary hypothyroidism					Central hypothyroidism ( Secondary and Tertiary )							Congenital hypothyroidism
Auto immune	Drug induced	Iatrogenic	Transient Hypothyroidism	Infiltrative disorders	Genetic causes	Iatrogenic	Tumors	Vascular	Infiltrative	Infectious	Miscellaneous
Hashimotos thyroiditis Atrophic thyroiditis	Lithium Thionamides Amiodarone Iodine containing contrast agents Interferon - alfa Tyrosine kinase inhibitor	Subtotal or Total thyroidectomy Radioiodine therapy External radiation of the neck Iodine deficiency	Subacute granulomatous thyroiditis Postpartum thyroiditis Painless (silent, lymphocytic) thyroiditis	Amyloidosis Sarcoidosis Hemochromatosis Scleroderma Cystinosis Reidel's thyroiditis( fibrous thyroiditis )	TRH deficiency Isolated CeH Inactive TSH Inactive TRH receptor	Post pituitary surgery Post external radiation Drugs: Growth hormone therapy, Glucocorticoids, Retinoid X Receptor(RXR) agonists, Salicylates, Dopamine	Pituitary macroadenoma Craniopharyngioma Meningioma Glioma Rathke cleft cyst Metastatic	Hemorrhage: Pituitary apoplexy, Subarachnoid hemorrhage Ischemia: Postpartum pituitary necrosis Aneurysm	Hemochromatosis Histiocytosis Sarcoidosis	Syphilis Bacterial abscess Tuberculosis Toxoplasmosis	Transient: overreplacement of T4 in primary hypothyroidism, Sick euthyroid state Trauma: head injury	Thyroid dysgenesis Thyroid agenesis Thyroid dyshormonogenesis

Diagnosis

Shown below is an algorithm summarizing the diagnosis of [[hypothyroidism]]

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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

TPOAb (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, 4.Central hypothyroidism

Positive

Negative

Central hypothyroidism

Autoimmune thyroid disease (Hashimotos disease)

1. Euthyroid sick syndrome 2. External radiation 3. Drug induced 4. Iodine deficiency 5. Congenital hypothyroidism 6. Seronegative autoimmune thyroid disease

Brain MRI

Abnormal

Normal

Pituitary or Hypothlamus lesion

Congenital TRH, TSH deficiency, Infiltrative diseases

Treatment

Shown below is an algorithm summarizing the treatment of Primary hypothyroidism.

Primary hypothyroidism

TSH > 5.5mU/L, FT4 Low

TSH = 5.5 - 10 mU/L, FT4 Normal

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

Shown below is an algorithm summarizing the treatment of Central hypothyroidism.

Central hypothyroidism

TSH<0.5mU/L 0r 0.5-5.5mu/L, FT4 Low

Adrenal insufficiency

No

Yes

MRI Brain

Give glucocorticoids for 1-2 weeks to prevent adrenal crisis

Tumor

Levothyroxine

Present

Absent

Consider Surgery

Levothyroxine

Reassess by measuring FT4 Goal FT4 is upper limit of normal

Do's

• The content in this section is in bullet points.

Don'ts

• The content in this section is in bullet points.

References

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