Updated: 8/5/2020

Hypothyroidism vs. Hyperthyroidism

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Snapshot
  • A 32-year-old woman presents to the clinic complaining of fatigue and weight gain for the past 2 months. She endorses cold intolerance, constipation, and dry skin but denies fever, diarrhea, swelling, chest pain, or shortness of breath. A physical examination demonstrates a lethargic, stocky patient with brittle hair. Her past medical history is significant for asthma that is well controlled with her rescue inhaler. Her laboratory studies demonstrate elevated levels of thyroid stimulating hormone. (Hashimoto thyroiditis)
Hypothyroidism
  • Clinical definition  
    • disorder characterized by the under production of thyroid hormone  
  • Epidemiology  
    • demographics 
      • iodine deficiency is the most common cause of hypothyroidism worldwide  
      • Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas  
  • Pathogenesis
    • primarily due to thyroid disease (primary hypothyroidism) but can be caused by secondary and/or tertiary hypothyroidism
    • primary hypothyroidism
      • Hashimoto thyroiditis (chronic autoimmune thyroiditis)
        • cell- and antibody-mediated destruction of thyroid tissue
      • infiltrative disease (e.g., fibrous thyroiditis)
      • iatrogenic disease
        • thyroidectomy
        • radioiodine treatment
        • external radiation therapy
      • iodine deficiency and/or excess
      • thyroid hormone resistance 
      • medications
        • lithium
        • amiodarone
        • interferon alpha
        • interleukin-2
        • tyrosine kinase inhibitors
        • checkpoint inhibitor immunotherapy (e.g., ipilimumab, pembrolizumab, and nivolumab)
    • secondary and tertiary hypothyroidism
      • secondary hypothyroidism
        • caused by TSH deficiency secondary to any of the causes of hypopituitarism
        • most commonly due to a pituitary tumor
        • other causes include Sheehan syndrome, trauma, craniopharyngiomas, or infiltrative diseases
      • tertiary hypothyroidism
        • caused by any disorder that damages the hypothalamus or interferes with hypothalamic-pituitary portal blood flow (e.g., radiation therapy) 
Hyperthyroidism 
  • Clinical definition
    • disorder defined by the over activity of the thyroid leading to excess thyroxine, leading to an acceleration of the body’s metabolism
  • Epidemiology
    • demographics
      • more common in women than men (5:1 ratio)
      • Grave disease is the most common cause of hyperthyroidism
  • Pathogenesis
    • increased synthesis of thyroxine or from the release of preformed hormone secondary to inflammation or destruction of thyroid tissue causing a low TSH 
    • increased de novo synthesis of thyroxine
      • Grave disease 
        • autoimmune disorder resulting from thyroid-stimulating hormone (TSH) receptor antibodies
        • stimulates thyroid gland growth and thyroid hormone synthesis and release
      • toxic adenoma/toxic multinodular goiter 
        • hyperplasia of thyroid follicular cells that are independent of TSH regulation
        • presents with a nontender palpable nodule and focal uptake on radioactive iodine uptake studies
      • trophoblastic disease/germ cell tumors
        • high level human chorionic gonadotropin (hCG) from these conditions will lead to thyrotropic activity
      • ectopic TSH secretion
        • TSH-producing pituitary adenomas
    • release of preformed hormone
      • thyroiditis
        • inflammation of thyroid tissue
      • exogenous ingestion
      • ectopic production of thyroid hormone
        • struma ovarii 
Presentation
  • Symptoms/Physical exam
Hypothyroidism
Hyperthyroidism
  • Cold intolerance (↓ heat production)
  • Heat intolerance (↑ heat production)
  • Weight gain and ↓ appetite
  • Weight loss and ↑ appetite
  • Hypoactivity, lethargy, fatigue, and weakness
  • Hyperactivity
  • Constipation
  • Diarrhea
  • ↓ Reflexes
  • ↑ Reflexes
  • Bradycardia
  • Tachycardia, palpitations, arrhythmias
  • Dry, cool skin and coarse, brittle hair
  • Warm, moist skin and fine hair
  • Diastolic hypertension 
  • Systolic hypertension
  • Myxedema (facial/periorbital)
  • Osteoporosis and hypercalcemia 
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  • Apathetic thyrotoxicosis
 
Studies
  • Diagnostic testing
    • diagnostic approach
      • diagnosis is based on clinical suspicion and confirmed via thyroid function tests
  • Labs
Hypothyroidism
Hyperthyroidism
  • ↑ TSH (best first test)
  • ↓ TSH (best first test) 
  • ↓ Total T4
  • ↑ Total T4
  • ↓ Free T4
  • ↑ Free T 
  • Hypercholesterolemia (↓ LDL receptor synthesis)
  • Hypocholesterolemia (↑ LDL receptor synthesis)
 
Treatment
 
Hypothyroidism
Hyperthyroidism
  • Levothyroxine
  • Thionamides (e.g., methimazole)
  • Ablative 131I therapy
  • Propranolol (rate/symptom control) 
 
Complications
  • Myxedema coma (hypothyroidism) 
  • Thyroid storm (hyperthyroidism)
 

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(M3.EC.14.9) An 86-year-old woman is brought to the emergency department from her nursing home facility. She has been more fatigued and less communicative over the past 3 days. The patient's only complaint is generalized weakness. She has had no witnessed falls and no signs of trauma during this time frame. Her past medical history is significant for mild dementia, well-controlled hypertension, and hyperlipidemia. Her medications include hydrochlorothiazide, losartan, and simvastatin. Her temperature is 97.6°F (36.4°C), blood pressure is 133/83 mmHg, pulse is 120/min, respirations are 16/min, and oxygen saturation is 98% on room air. Neurologic exam is unremarkable. There are no signs of trauma upon inspection. An ECG is performed as seen in Figure A. A previous ECG performed 2 weeks ago demonstrated normal sinus rhythm. An initial CBC, troponin, and serum chemistry are within normal limits. A chest radiograph, urinalysis, lumbar puncture, and flu swab are negative for any source of infection. Which of the following is the best next step in management? Tested Concept

QID: 102950
FIGURES:
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Cardiac catheterization

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CT head

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Electrophysiologic studies

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Holter monitoring

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Thyroid-stimulating hormone (TSH)

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