What is the most likely diagnosis for a patient who had an upper respiratory tract infection 5 days ago and suddenly developed loss of consciousness and difficulty breathing, now requiring intubation?

Most Likely Diagnosis: Myasthenia Gravis

The most likely diagnosis is myasthenia gravis (Option C), presenting as myasthenic crisis triggered by the recent upper respiratory tract infection. 1

Clinical Reasoning

Why Myasthenia Gravis is Most Likely

The clinical presentation is pathognomonic for myasthenic crisis:

• Upper respiratory tract infections are well-established triggers for myasthenic crisis, causing acute decompensation in patients with underlying neuromuscular disease 1
• The temporal relationship between URTI onset (5 days ago) and severe symptom development fits the typical pattern of infection-triggered myasthenic crisis, where respiratory muscle weakness progresses rapidly to respiratory failure requiring mechanical ventilation 1
• Loss of consciousness in the context of neuromuscular weakness suggests hypercapnic respiratory failure from inadequate ventilation, not primary pulmonary pathology 1
• The combination of difficulty breathing and altered consciousness requiring intubation is characteristic of myasthenic crisis 1

Why Other Options Are Less Likely

COPD (Option A):

• COPD exacerbations typically occur in patients with known chronic lung disease and progress over days with worsening dyspnea, not sudden loss of consciousness as the primary feature 2
• The sudden onset after URTI without prior respiratory history makes this unlikely

Pulmonary Edema (Option B):

• Cardiogenic pulmonary edema would typically present with signs of fluid overload, elevated jugular venous pressure, and peripheral edema 2
• While noncardiogenic pulmonary edema can complicate upper airway obstruction, it requires mechanical obstruction (like epiglottitis), not simple URTI 3, 4
• Loss of consciousness is not a typical presenting feature of pulmonary edema 5

Drug Overdose (Option D):

• No history of drug exposure is mentioned
• The temporal relationship with URTI makes infectious trigger of underlying disease more likely

Critical Diagnostic Considerations

Infections, particularly respiratory infections, are among the most common precipitants of myasthenic crisis, accounting for a significant proportion of cases requiring ICU admission 1

Myasthenic crisis can present acutely in previously undiagnosed patients, with respiratory infection being the unmasking event 1

Common Pitfalls to Avoid

• Do not assume all respiratory failure post-URTI is pneumonia—the absence of fever, purulent secretions, or infiltrates on chest radiograph should prompt consideration of neuromuscular causes 1
• Do not delay neurological evaluation in patients with unexplained respiratory failure requiring intubation, especially when preceded by infection 1

Immediate Next Steps

Once intubated, the patient requires:

• Assessment for underlying neuromuscular disease, including bedside pulmonary function testing, acetylcholine receptor antibodies, and neurological consultation 1
• Avoid medications that can worsen myasthenia gravis, including aminoglycosides, fluoroquinolones, and neuromuscular blocking agents 1
• Continuous monitoring with waveform capnography to detect changes in ventilation 1