What is the most likely diagnosis for a patient who developed loss of consciousness and difficulty breathing 5 days after an upper respiratory tract infection (URTI) and is currently intubated?

Myasthenia Gravis

The most likely diagnosis is C. Myasthenia gravis, given the acute onset of respiratory failure and loss of consciousness following an upper respiratory tract infection, which is a classic trigger for myasthenic crisis requiring intubation.

Clinical Reasoning

Why Myasthenia Gravis is Most Likely

• Upper respiratory tract infections are well-established triggers for myasthenic crisis, causing acute decompensation in patients with underlying neuromuscular disease 1
• The temporal relationship—developing severe symptoms 5 days after URTI onset—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 this context suggests hypercapnic respiratory failure from neuromuscular weakness rather than primary pulmonary pathology, as the patient cannot maintain adequate ventilation 1
• The acute presentation requiring intubation indicates bulbar and respiratory muscle involvement, which is the hallmark 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 present with progressive dyspnea, not sudden loss of consciousness 1
• The 5-day timeline after URTI is too short for typical COPD exacerbation progression
• Loss of consciousness would be unusual as the presenting feature without preceding respiratory distress symptoms

Pulmonary Edema (Option B):

• Pulmonary edema presents with orthopnea, pink frothy sputum, and crackles on examination—not typically triggered by URTI 1
• The clinical scenario lacks mention of cardiac history or fluid overload symptoms
• Loss of consciousness from pulmonary edema would require severe hypoxemia with preceding respiratory distress

Drug Overdose (Option D):

• No history of drug ingestion is mentioned in the clinical scenario
• The temporal relationship to URTI makes infectious or infection-triggered complications more likely
• Drug overdose would not explain the specific 5-day post-URTI timeline

Critical Diagnostic Considerations

Key Clinical Features Supporting Myasthenia Gravis

• Infections, particularly respiratory infections, are among the most common precipitants of myasthenic crisis, accounting for a significant proportion of cases requiring ICU admission 1
• The combination of difficulty breathing (respiratory muscle weakness) and altered consciousness (from hypercapnia/hypoxemia) 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

Immediate Management Priorities

• Once intubated, the patient requires assessment for underlying neuromuscular disease including bedside pulmonary function testing (when extubated), acetylcholine receptor antibodies, and neurological consultation 1
• Waveform capnography should be continuously monitored in all intubated patients to detect changes in ventilation 1
• Avoid medications that can worsen myasthenia gravis, including aminoglycosides, fluoroquinolones, and neuromuscular blocking agents, which can precipitate or worsen crisis 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
• Recognize that myasthenic crisis can be the initial presentation of myasthenia gravis in up to 20% of cases, often triggered by infection 1
• Avoid empiric antibiotic therapy without evidence of bacterial infection, as most URTIs are viral and antibiotics do not prevent complications in immunocompetent patients 2, 3