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

Myasthenia Gravis (Myasthenic Crisis)

The most likely diagnosis is C. Myasthenia gravis, specifically myasthenic crisis triggered by the upper respiratory tract infection. 1

Clinical Reasoning

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 sudden severe symptom development (loss of consciousness and respiratory failure requiring intubation) fits the classic pattern of infection-triggered myasthenic crisis. 1

Key Diagnostic Features Supporting Myasthenia Gravis

• Loss of consciousness in the context of neuromuscular weakness indicates hypercapnic respiratory failure from inadequate ventilation, not primary cardiac or pulmonary pathology 1
• The combination of difficulty breathing and altered consciousness requiring intubation is pathognomonic for myasthenic crisis 1
• Myasthenic crisis can present acutely in previously undiagnosed patients, with respiratory infection being the unmasking event 1
• Infections, particularly respiratory infections, are among the most common precipitants of myasthenic crisis, accounting for a significant proportion of cases requiring ICU admission 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, increased sputum production, and cough 1
• Sudden loss of consciousness is not a typical presenting feature of COPD exacerbation 1

Pulmonary Edema (Option B)

• Pneumonia or pulmonary edema would typically present with fever, productive cough, and radiographic infiltrates, not sudden loss of consciousness as the primary feature 1
• The absence of fever, purulent secretions, or infiltrates on chest radiograph should prompt consideration of neuromuscular causes 1

Drug Overdose (Option D)

• No history of drug exposure is mentioned in the clinical scenario
• The temporal relationship with URTI makes infection-triggered neuromuscular crisis far more likely

Immediate Management Steps

Diagnostic Workup

• Assess for underlying neuromuscular disease with bedside pulmonary function testing, acetylcholine receptor antibodies, and immediate neurological consultation 1
• Do not delay neurological evaluation in patients with unexplained respiratory failure requiring intubation, especially when preceded by infection 1

Critical Medication Considerations

• Avoid medications that can worsen myasthenia gravis, including aminoglycosides, fluoroquinolones, and neuromuscular blocking agents, which can precipitate or worsen crisis 1
• If neuromuscular blockade was used during intubation, this could have worsened the underlying condition 1

Ventilatory Management

• Maintain mechanical ventilation with appropriate settings, avoiding excessive tidal volumes that could worsen respiratory mechanics 1
• Monitor with continuous waveform capnography to detect changes in ventilation 1

Critical Pitfall to Avoid

Do not assume all respiratory failure post-URTI is pneumonia—the absence of fever, purulent secretions, or infiltrates on chest radiograph should immediately prompt consideration of neuromuscular causes. 1 This is the most common diagnostic error in this clinical scenario.