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?

Most Likely Diagnosis: Myasthenia Gravis (Option C)

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

Clinical Reasoning

Why Myasthenia Gravis is the Answer

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 fits the typical pattern of infection-triggered myasthenic crisis, where respiratory muscle weakness progresses rapidly to respiratory failure requiring mechanical ventilation. 1

The combination of difficulty breathing and loss of consciousness requiring intubation is pathognomonic for myasthenic crisis. 1 The loss of consciousness in this context suggests hypercapnic respiratory failure from inadequate ventilation due to neuromuscular weakness, rather than primary pulmonary or cardiac pathology. 1

Critical Diagnostic Pattern

• 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
• The sudden deterioration after a seemingly routine URTI is the key distinguishing feature that points away from other diagnoses. 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—sudden loss of consciousness is not a typical presenting feature. 1 This patient has no mentioned history of chronic lung disease, and the acute presentation following URTI does not fit the typical COPD exacerbation pattern. 1

Pulmonary Edema (Option B)

Pulmonary edema would typically present with progressive dyspnea, orthopnea, crackles on examination, and evidence of fluid overload or cardiac dysfunction. The absence of these features and the specific temporal relationship with URTI makes this diagnosis unlikely. 1

Drug Overdose (Option D)

There is no mention of drug exposure, altered mental status prior to respiratory failure, or toxidrome features. The clear temporal relationship with URTI and the pattern of respiratory muscle failure leading to hypercapnic respiratory failure points away from overdose. 1

Critical Management 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 prompt consideration of neuromuscular causes. 1 Pneumonia would typically present with fever, productive cough, and radiographic infiltrates, not sudden loss of consciousness as the primary feature. 1

Do not delay neurological evaluation in patients with unexplained respiratory failure requiring intubation, especially when preceded by infection. 1 Once intubated, this patient requires immediate assessment for underlying neuromuscular disease, including bedside pulmonary function testing, acetylcholine receptor antibodies, and neurological consultation. 1