Myxoedema Coma

Life-threatening manifestation of hypothyroidism characterised by a combination of:

This covers myxoedema coma, general considerations of hypothyroidism are covered at Hypothyroidism.

Note that the name is a misnomer and patients typically present with neither myxoedema or coma.

Epidemiology and Risk Factors

Pathophysiology

Aetiology

Typically presents with pre-existing untreated (or undiagnosed) hypothyroidism, exacerbated by some precipitant:

  • Cessation of usual thyroid supplementation
  • Physiological stress
    • Infection
    • Hypothermia
    • Trauma
      • Surgery
      • Burns
    • DKA
    • CVA
    • Cardiac failure
  • Medications
    • Amiodarone
    • Anaesthetic agents
    • Analgesics
    • β-blockers
    • Diuretics
    • Lithium
    • Phenytoin

Clinical Manifestations

  • B
    • Weakness
    • Pleural effusions
    • OSA
  • C
    • Bradycardia
    • ↓ CO
    • Diastolic hypertension
  • D
    • ↓ GCS
    • Weakness
    • Fatigue
    • Psychiatric alterations
  • F
    • Bladder distension
    • Urinary retention
  • G
    • Distension
    • Ileus
    • Faecal impaction

Diagnostic Approach and DDx

Investigations

Bedside:

  • ABG
    • Respiratory alkalosis
      Due to ↓ metabolic rate and ↓ CO2 production.

Laboratory:

  • Blood
    • FBE
      • Normocytic anaemia
    • UEC
      • Hyponatraemia
        Due to free water retention.
      • Hypoglycaemia
      • Hypophosphataemia
    • TFTs
      • ↓ T4/T3
      • Variable TSH
        • ↑ In primary hypothyroidism
        • ↓ In secondary and tertiary hypothyroidism
    • Cortisol
      Prior to commencing hydrocortisone.

Imaging:

Other:

Management

  • Thyroid hormone supplementation
    Note that rapid replacement may precipitate cardiac ischaemia and malignant arrhythmias.
  • Adrenal replacement with corticosteroids

Resuscitation:

  • A
    • Intubation and ventilation may be required for respiratory failure
  • C
    • Volume resuscitation
      Cautiously due to risk of APO.
    • Chronotropy
      May require pacing.
  • D
    • Dextrose replacement

Specific therapy:

Dosing of thyroxine should be adjusted for age and frailty, with lower doses used for patients at ↑ risk of adverse cardiac events relating to rapid replacement.

  • Pharmacological
    • Thyroid replacement
      • Thyroxine (T4)
        • Generally preferred agent
        • Load: Levothyroxine 200-500μg IV
        • Maintenance: Levothyroxine 100-300μg IV daily thereafter
          Can be converted to PO formulation.
      • T3
        • More active than T4
        • More rapid onset of action
        • Expensive
        • Possible ↑ risk of iatrogenic harm
    • Corticosteroids
      • Hydrocortisone 100mg Q8H
        Cease if random cortisol normal.
  • Procedural
  • Physical

Supportive care:

  • C
    • Avoid vasoactives
      If possible, to ↓ arrhythmia risk.
  • E
    • Rewarming
      • Passive usually adequate
      • Active may be required
  • G
    • Feeding
      ↑ Risk of intolerance with gastrointestinal stasis.

Marginal and Ineffective Therapies

Anaesthetic Considerations

Complications

  • Death
  • E
    • Adrenal insufficiency
    • Refractory hypothermia

Prognosis

  • Mortality >50%

Key Studies

References

  1. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.