Hypothyroidism resident survival guide

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Hypothyroidism Resident Survival Guide Microchapters

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ayeesha Kattubadi, M.B.B.S[2]

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. [1]


Hypothyroidism can be classified based on the location of the pathology or based on etiology as shown in the table below.[2][3][4][5][6]

Life Threatening Causes

Common Causes

Causes of hypothyroidism
Primary hypothyroidism Central hypothyroidism

( Secondary and Tertiary )

Congenital hypothyroidism
Autoimmune Drug induced Iatrogenic Transient Hypothyroidism Infiltrative disorders Genetic causes Iatrogenic Tumors Vascular Infiltrative Infectious Miscellaneous
  • TRH deficiency
  • Isolated CeH
  • Inactive TSH
  • Inactive TRH receptor


Shown below is an algorithm summarizing the diagnosis of hypothyroidism: [7][8][9][10][11]

Signs and Symptoms of hypothyroidism are present.
TSH, free T4 (FT4)
TSH >5.5mU/L
TSH 0.5-5mU/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,
4.Central hypothyroidism
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
Pituitary or Hypothlamus lesion
Congenital TRH, TSH deficiency,
Infiltrative diseases


Shown below is an algorithm summarizing the treatment of Primary hypothyroidism. [12][13]

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
Goal TSH = 0.4-4mU/L
Adjust levothyroxine dose if goal TSH not reached
Levothyroxine trial for 3-6 months.
(Thyroid Peroxidase) Antibodies
Symptoms of hypothyroidism
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. [14]

Central hypothyroidism
0r 0.5-5.5mu/L, FT4 Low
Adrenal insufficiency
MRI Brain
Give glucocorticoids for 1-2 weeks to prevent adrenal crisis
Consider Surgery
Reassess by measuring FT4
Goal FT4 is
upper limit of normal




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  9. Fitzgerald SP, Bean NG, Falhammar H, Tuke J (2020). "Clinical Parameters Are More Likely to Be Associated with Thyroid Hormone Levels than with Thyrotropin Levels: A Systematic Review and Meta-analysis". Thyroid. doi:10.1089/thy.2019.0535. PMID 32349628    32349628   Check |pmid= value (help).
  10. Peeters RP (2017). "Subclinical Hypothyroidism". N Engl J Med. 376 (26): 2556–2565. doi:10.1056/NEJMcp1611144. PMID 28657873.
  11. Persani L, Brabant G, Dattani M, Bonomi M, Feldt-Rasmussen U, Fliers E; et al. (2018). "2018 European Thyroid Association (ETA) Guidelines on the Diagnosis and Management of Central Hypothyroidism". Eur Thyroid J. 7 (5): 225–237. doi:10.1159/000491388. PMC 6198777. PMID 30374425.
  12. Okosieme O, Gilbert J, Abraham P, Boelaert K, Dayan C, Gurnell M; et al. (2016). "Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee". Clin Endocrinol (Oxf). 84 (6): 799–808. doi:10.1111/cen.12824. PMID 26010808.
  13. Chakera AJ, Pearce SH, Vaidya B (2012). "Treatment for primary hypothyroidism: current approaches and future possibilities". Drug Des Devel Ther. 6: 1–11. doi:10.2147/DDDT.S12894. PMC 3267517. PMID 22291465.
  14. Persani L (2012). "Clinical review: Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges". J Clin Endocrinol Metab. 97 (9): 3068–78. doi:10.1210/jc.2012-1616. PMID 22851492.
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