What can precipitate a myasthenia crisis?

Precipitating Factors for Myasthenic Crisis

Infections are the most common precipitant of myasthenic crisis, followed by medication changes (particularly steroid withdrawal or initiation), and exposure to contraindicated drugs that worsen neuromuscular transmission. 1, 2, 3

Infectious Triggers

• Respiratory infections and pneumonia are the leading precipitants of myasthenic crisis, accounting for the majority of cases. 2, 3, 4
• Sepsis from any source can trigger decompensation requiring mechanical ventilation. 3
• Urinary tract infections represent another common infectious trigger. 5
• CMV pneumonitis has been documented as a precipitating factor in critically ill patients. 4

Medication-Related Precipitants

Contraindicated Medications That Must Be Avoided

The following medications can directly precipitate or worsen myasthenic crisis and should be strictly avoided: 1, 6

• Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) 1, 6, 7
• Aminoglycoside antibiotics (gentamicin, tobramycin) 1, 6
• Macrolide antibiotics (erythromycin, azithromycin) 1, 6, 7
• Beta-blockers 1, 6
• Intravenous magnesium - this is particularly dangerous as it directly impairs neuromuscular transmission and can precipitate respiratory failure 1, 8
• Neuromuscular blocking agents (especially depolarizing agents like succinylcholine; nondepolarizing agents require dose reduction) 7, 2
• Barbiturate-containing medications (butalbital/Fioricet) 6

Immunosuppressive Medication Changes

• Rapid tapering or withdrawal of corticosteroids is a well-documented precipitant. 3, 4, 9
• Paradoxically, initiating high-dose corticosteroids can trigger crisis in the first 1-2 weeks of treatment due to initial worsening before improvement occurs. 3, 4, 9
• Withdrawal or reduction of acetylcholinesterase inhibitors (pyridostigmine) without appropriate supervision. 4, 9

Drug Interactions

• Concomitant use of anticholinesterase agents and corticosteroids may produce severe weakness, and if anticholinesterase agents must be combined with steroids, close supervision with respiratory support availability is essential. 7

Physiological Stressors

• Surgical procedures and anesthesia represent significant risk, particularly in patients with oropharyngeal or respiratory muscle weakness who have not received preoperative immunotherapy. 3
• Pregnancy and menstruation can precipitate crisis through hormonal fluctuations. 4
• Aspiration events due to bulbar weakness can rapidly lead to respiratory decompensation. 3, 10

Clinical Context and Red Flags

Myasthenic crisis typically occurs within the first 2 years of disease diagnosis, with up to 20% of patients experiencing crisis as their initial presentation of previously undiagnosed myasthenia gravis. 10

The lifetime risk of experiencing at least one crisis is 15-20% for all myasthenia patients, with a 30% recurrence risk after the first episode. 10

Critical warning signs of impending crisis include: 10

• Rapidly progressive weakness of respiratory and bulbar muscles developing over minutes to days
• Severe dyspnea and respiratory insufficiency
• Globus sensation with exhausting coughing and swallowing difficulty
• Aspiration risk

Common Pitfalls to Avoid

Do not administer edrophonium (Tensilon) testing during suspected crisis - acetylcholinesterase inhibitors should be avoided entirely during acute crisis. 2

Do not initiate corticosteroids during acute crisis - wait until after immunotherapy (plasmapheresis or IVIG) has been started and respiratory status is stabilized. 2

Do not overlook occult infections - thoroughly investigate for respiratory, urinary, and other sources of infection as these are the most common precipitants. 2, 3, 4