Study guide:

Definition:

  • Simply, decrease in circulating thyroid hormones with an increase in TSH.

 

Types:

  • Primary (caused by conditions related to the thyroid gland)

  • Secondary (caused by conditions related to pituitary gland)

  • Tertiary (caused by condition related to hypothalamus)

 

Causes:

  • Primary causes: (MOST COMMON):

    • Hashimatto (chronic thyroiditis):

      • Most common cause in developed country. 

      • Autoimmune.

      • Caused by autoantibodies (antithyroperoxidase and antimicrosomal ‘anti-TPO’ antibodies).

    • Iodine deficiency:

      • Most common cause in developing country. 

    • Iatrogenic:

      • Drugs (lithium, amiodarone).

      • RAI (causes thyroid destruction).

      • Thyroid removal surgery.

    • Congenital (cretinism)

Diagnosis:

  • Best initial/most useful screening test is measuring serum TSH level. 

  • If TSH is increased:

    • Check free T4  → decreased or normal:

      • Decreased → primary hypothyroidism.

      • Normal → subclinical hypothyroidism (increase in TSH could still manage the problem and cause thyroid hormone secretion).

  • If TSH is decreased:

    • Check T4 → decreased → Secondary hypothyroidism

  • If TSH is normal but the symptoms strongly suggest hypothyroidism:

    • Check T4 → decreased or normal:

      • Decreased → secondary hypothyroidism →  Do imaging (for patient with sarcidosis, head injury, cancer or under radiotherapy)

      • Normal → no further evaluation

  • If structural abnormalities suspected → US or radioneuclic scanning.  

  • Secondary and tertiary causes:

    • Tumor.

    • Necrosis (e.g: shehann).

    • Pituitary or hypothalamic failure.

  • Transient hypothyroidism:

    • Caused by subacute or lymphatic thyroiditis

    • Reverses in 2-8 months. 

Symptoms:

  • Most common complaint is weakness

  • Lethargy

  • Cold intolerance

  • Weight gain (decreased basal metabolic rate)​​​

  • Period irregularities in females (oligomenorrhea)

  • Decreased cognition

  • Constipation

  • Depression

Signs:

  • Most common sign is coarse or dry skin

  • Slow speech

  • Eyelid edema

  • Non-pitting edema

  • Puffy face

  • Carpel tunnel

  • Hoarseness

  • Goiter (Rubbery, non-tender)

  • Increase in cholesterol level

High TSH (X2 of normal) + normal T4 = Treatment!

Treatment:

  • Lifelong levothyroxine.

  • Dose 1.6 mcg\kg.

  • In young healthy individuals with no heart disease → start the full replacement dose

  • In individuals who are 60 year and older OR with heart diseases → start with 12.5-25 mcg → then titer 25-50 mcg every 6 weeks.​

    • In these groups full dose increases the risk of angina, MI, HF, & arrhythmia!

  • Needs 6 weeks for TSH to go back to normal.

  • With the treatment, keep TSH in the lower half of the normal reference range (0.4-2.5).

  • Do not decrease TSH below 0.4 à osteoporosis and atrial fibrillation risks.

  • Increase the dose by 75% in case of pregnancy.

  • Treat subclinical hypothyroidism in case of:

    • Patient with goiter

    • Hypercholestremia

    • Symptoms of hypothyroidism

    • TSH is more than 20

  • In case of secondary hypothyroidism give hydrocortisone with the thyroxin.

Follow-up:

  • In tittering or any change in dose, asses the TSH every 6 weeks.

  • When TSH is normal follow up every 6 months to 1 year.​

References:  

  • Agabegi S, Agabegi E, Ring A. Step-up to medicine. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2013.

  • Aafp.org. Thyroid and Parathyroid Disorders - American Family Physician [Internet]. 2015 [cited 23 December 2015]. Available from: http://www.aafp.org/afp/topicModules/viewTopicModule.htm?topicModuleId=67 

  • Lipsky M, King M. Blueprints family medicine. Baltimore, MD: Lippincott Williams & Wilkins; 2011.

  • Sattar H. Fundamentals of pathology. Chicago: Pathoma.com; 2011.

  • Kaplan. Kaplan lecture notes, Medicine, 2014.

Written by:         Rawan Al-Tuwaijri      


Reviewed by:       Jumana AlJohani
                             Bassam Alghamdi


​Format Editor:     Roaa Amer

Website publisher: Adel Yasky

                                Bayan Alzomaili