Medical Musing of the Week: Hyperthyroidism

Overview

  • Excess Synthesis and secretion of thyroid hormone by the thyroid gland
  • Hyperthyroidism exists as Graves Disease, Toxic Multinodular Goiter, Toxic Adenoma and Subacute Thyroiditis
  • The MCC of hyperthyroidism is Graves Disease  (50-60%)
  • Increased FT4 
  • Increased T3 in Subacute Thyroiditis
  • TSH is suppressed 

Pathophysiology

  • TRH is produced in the Hypothalamus which then signals the Pituitary Gland to secrete TSH to the Thyroid Gland signaling T3 and T4 to be released to peripheral tissues (see picture below if you are a visual learner.  C/o Medscape)
  • When adequate levels of circulating T3 and T4 have been achieved in the normally functioning thyroid a negative feedback signal is sent to hypothalamus to temporarily halt TRH production (and begin reproducing when T3 and T4 levels are low in periphery) 
  • Iodide binds to thyroglobulin via peroxidase.  This results in monoiodotyrosine (MIT) and Diiodotyrosine–combining to form T3 + T4 which are then stored in the thyroid as preformed hormone (these were terms I haven’t seen since didactic year, hah!)

image

Etiology & Risk Factors

  • Genetic predisposition
  • Additional Autoimmune diagnosis
  • Pregnancy (Use PTU not MTU)
  • Women > Men
  • 20-40’s
  • Amiodarone toxicity (rare)

Clinical Manifestations

History

  • Nervousness/Restlessness
  • Increased bowel movements
  • Anxiety
  • Palpitations
  • Weakness
  • Menstrual Irregularities 

Physical Exam

image
Exopthalmos
  • Fine resting tremor
  • Warm skin/heat intolerance
  • Thinning hair
  • Increased reflexes
  • Onycholysis
  • Enlarged thyroid
  • Sinus tachycardia/PAC’s/A-Fib
  • Exopthalmos

    image
    Pre-tibial Myxedema
  • Upper eyelid retraction
  • Lid lag w/ downward gaze
  • Pretibial Myxedema

Diagnosis

  • The single most important test is TSH (will be decreased)
  • The severity of clinical manifestations does not necessarily correlate with TSH level
  • ELISA for Anti-TPO for Graves Disease
  • Free T4 and Total T3 levels
  • EKG if Sinus Tachycardia (may also want to check electrolytes) 

Treatment

  • Methimazole
    • Starting dose: 5-20mg Q8h
    • Once euthyroid 5-15mg QD
    • Inhibit coupling of iodotyrosines in thyroglobulin resulting in a gradual decrease in circulating hormone over 2-8 weeks
    • Monitor levels Q4 weeks when first starting treatment
  • Propylthiouracil
    • Starting dose: 300-400mg/day divided Q8h
    • Once euthyroid 100-150mg Q8h
    • Preferred in pregnancy (MTU is safe after first trimester)
    • More potent–also blocks T4 -> T3
    • Inhibit coupling of iodotyrosines in thyroglobulin resulting in a gradual decrease in circulating hormone over 2-8 weeks
    • Monitor levels Q4 weeks when first starting treatment
  • MTU & PTU side effects:
    • Fever, Rash, Agranulocytosis, Aplastic Anemia, Hepatitis
  • Radioactive Iodine Ablation (most common and effective treatment)
image
Radioactive Iodine Ablation in a patient with Graves Disease
  • Thyroidectomy (not frequently performed due to effectiveness of RAI ablation)
  • Symptom relief (Beta blockers)
    • In addition to treating the symptoms of tachycardia, tremor etc– beta blockers also decrease conversion of T3 to T4 (which I didn’t know before!

Complications 

  • Patients who go through RAI ablation or thyroidectomy are often left hypothyroid.
  • Thyroid Storm
    • Acute life threatening hypermetabolic state caused by excessive thyroid hormone
    • Fever, tachycardia, hypertension, diaphoresis, AMS
    • Cardiac manifestations and complications can range from sinus tachycardia to high-output cardiac failure and arrhythmias 
    • Treatment
      • Methimazole is first line
        • 20mg Q4-6 hours
      • Propanolol is first line Beta Blocker
        • 60-80mg Q6h or .5-2mg IV Q10 minutes for the first few hours
      • Glucocorticoids
      • Supportive Measures

 

Sources:

Current Medical Diagnosis & Treatment 2015
UpToDate
Medscape

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