Learning objectives

• Describe the etiology and symptoms of hypothyroidism
• Diagnose and treat hypothyroidism
• Manage patients with hypothyroidism presenting for surgery

Background

• Hypothyroidism results from low levels of thyroid hormone
• Autoimmune thyroid disease and lack of dietary iodine are the most common causes
• Can range from asymptomatic to myxedema coma
• Can be treated with exogenous thyroid hormone

Etiology

• Primary hypothyroidism: The thyroid gland does not produce adequate amounts of thyroid hormone
  • Iodine deficiency
  • Autoimmune (Hashimoto thyroiditis)
  • Medications (amiodarone, thalidomide, oral tyrosine kinase inhibitors, stavudine, interferon, bexarotene, perchlorate, rifampin, ethionamide, phenobarbital, phenytoin, carbamazepine, interleukin-2, lithium)
  • Thyroid radioactive iodine therapy
  • Thyroid surgery
  • Radiotherapy to head or neck area
  • subacute granulomatous thyroiditis
  • Postpartum thyroiditis
• Secondary hypothyroidism: Thyroid gland is normal, pathology is related to pituitary gland or hypothalamus
  • Neoplastic, infiltrative, inflammatory, genetic, or iatrogenic disorders of the pituitary or hypothalamus
  • Sheehan syndrome
  • Thyrotropin-releasing hormone (TRH) resistance
  • TRH deficiency
  • Lymphocytic hypophysitis
  • Radiation therapy to the brain
  • Medications such as dopamine, prednisone, or opioids

Risk factors

• Women >60 years of age
• Pregnancy
• History of head and neck irradiation
• Autoimmune disorders
• Type I diabetes mellitus
• Positive thyroid peroxidase antibodies
• Family history of hypothyroidism

Signs & symptoms

• Cold intolerance
• Puffiness
• Decreased sweating
• Dry skin
• Hair loss
• Constipation
• Fatigue
• Muscle cramps
• Sleep disturbance
• Menstrual cycle abnormalities
• Weight gain
• Galactorrhea
• Depression
• Anxiety
• Psychosis
• Cognitive impairments
• Carpal tunnel syndrome
• Sleep apnea
• Hyponatremia
• Hypercholesterolemia
• Congestive heart failure
• Prolonged QT interval
• Fullness of throat
• Painless thyroid enlargement
• Episodic neck pain/sore throat
• Pallor and jaundice
• Dull facial expressions
• Macroglossia
• Bradycardia
• Pericardial effusion
• Prolonged ankle reflex relaxation time

Diagnosis

• Serum thyroid stimulating hormone (TSH) level to test for primary hypothyroidism
• Serum-free T4 level to test for secondary hypothyroidism
• Serum anti-thyroid antibodies to test for autoimmune thyroid disease
• Other laboratory tests may reveal hyperlipidemia, elevated serum CK, elevated hepatic enzymes, anemia, blood urea nitrogen, creatinine, and uric acid levels

Differential diagnosis

• Euthyroid sick syndrome
• Goiter
• Myxedema coma
• Anemia
• Riedel thyroiditis
• Subacute thyroiditis
• Thyroid lymphoma
• Iodine deficiency
• Addison disease
• Chronic fatigue syndrome
• Depression
• Dysmenorrhea
• Erectile dysfunction
• Familial hypercholesterolemia
• Infertility

Treatment

• Main treatment: levothyroxine monotherapy 1.6 µg/kg per day
• Lower the dose in elderly and atrial fibrillation patients
• IV levothyroxine in patients who cannot take it orally (half of the oral dose)
• Treat adrenal insufficiency first

Anesthetic management

TSH, thyroid stimulating hormone; T3, triiodothyronine; T4, thyroxine

Suggested reading

• Patil N, Rehman A, Jialal I. Hypothyroidism. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519536/
• Farling PA. Thyroid disease. BJA: British Journal of Anaesthesia. 2000;85(1):15-28.
• Palace MR. Perioperative Management of Thyroid Dysfunction. Health Serv Insights. 2017;10:1178632916689677. Published 2017 Feb 20.

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