What focused history should be obtained for a patient with known myasthenia gravis presenting with shortness of breath?

Focused History for Known Myasthenia Gravis with Shortness of Breath

In a patient with known myasthenia gravis presenting with shortness of breath, immediately assess for myasthenic crisis by determining the rapidity of symptom onset, presence of bulbar weakness (dysphagia, dysarthria), ability to count to 15 in one breath, and any recent infection or medication changes—this presentation demands urgent evaluation for impending respiratory failure. 1, 2

Critical Red Flags Requiring Immediate ICU Assessment

• Timing and progression of weakness – Determine whether weakness developed over minutes, hours, or days, as rapid progression (within minutes to days) signals myasthenic crisis requiring immediate ICU admission and mechanical ventilation 2, 3

• Bulbar symptoms – Specifically ask about dysphagia, drooling, difficulty swallowing secretions, and dysarthria, as bulbar weakness is present in more than 50% of cases preceding myasthenic crisis and represents a key early warning sign for impending respiratory failure 1, 4

• Respiratory distress indicators – Ask whether the patient experiences breathlessness at rest, breathlessness while talking, or inability to count to 15 in a single breath, as these indicate imminent respiratory insufficiency 5, 1

• Aspiration risk – Inquire about choking episodes, coughing while eating or drinking, and globus sensation, as these may be life-threatening due to rapidly exhausting coughing and swallowing dysfunction 2

Precipitating Factors

• Infection history – Infection is the most common precipitant of myasthenic crisis; systematically ask about fever, cough, urinary symptoms, skin infections, or any recent infectious illness 3, 6

• Recent medication changes – Specifically inquire about new prescriptions of β-blockers, IV magnesium, fluoroquinolones (especially moxifloxacin), aminoglycosides, or macrolides, as these medications exacerbate myasthenia gravis and can precipitate crisis 1, 4, 6

• Immune checkpoint inhibitors – Ask about any cancer treatment with checkpoint inhibitors, as these must be permanently discontinued if they precipitated the crisis 4

• Medication compliance – Determine whether the patient has been taking pyridostigmine, corticosteroids, or other immunosuppressants as prescribed, as non-compliance can trigger decompensation 2

Disease-Specific History

• Baseline functional status – Establish the patient's usual level of weakness, ability to perform activities of daily living, and MGFA classification (Class I-V) to determine degree of acute deterioration 1, 4

• Previous crisis history – Ask about prior episodes of respiratory failure or ICU admissions, as the lifetime risk of recurrence is approximately 30% 2

• Current myasthenia treatment regimen – Document all current medications including pyridostigmine dose (maximum 120 mg four times daily), corticosteroid dose, and any steroid-sparing agents like azathioprine 1, 4

• Thymoma status – Determine whether the patient has had thymectomy or known thymoma, as this affects prognosis and management 4

Symptom Characterization

• Pattern of weakness – Ask whether weakness worsens with repetitive activity and improves with rest, as this fatigable pattern is characteristic of myasthenia gravis 1

• Distribution of weakness – Determine whether weakness is generalized (affecting limbs, trunk, respiratory muscles) versus isolated ocular or bulbar symptoms, as this guides severity classification 1, 4

• Ocular and facial symptoms – Ask about diplopia, ptosis, facial weakness, and difficulty closing eyes, even though the primary complaint is respiratory, as these help confirm the diagnosis and assess disease extent 1

Respiratory-Specific Assessment

• Orthopnea – Ask whether shortness of breath worsens when lying flat, as diaphragmatic weakness causes positional dyspnea in myasthenia gravis 2

• Nocturnal symptoms – Inquire about sleep disruption, morning headaches, or daytime somnolence, which may indicate nocturnal hypoventilation from respiratory muscle weakness 2

• Cough effectiveness – Ask about ability to cough forcefully and clear secretions, as diminished cough reflex is a reason for ICU admission 5

Common Pitfalls to Avoid

• Do not attribute all respiratory symptoms to pulmonary disease – When patients with known myasthenia gravis present with respiratory failure without clear pulmonary pathology and demonstrate persistent failure to wean from ventilatory support despite treatment of the presumed pulmonary condition, strongly consider myasthenic crisis as the primary diagnosis 7, 8

• Do not delay ICU transfer – The median duration of mechanical ventilation in myasthenic crisis is 12-14 days, and up to 22% of patients require ventilation within the first week; early recognition and ICU admission markedly reduce mortality 5, 2

• Avoid edrophonium testing in crisis – All acetylcholinesterase inhibitors, including edrophonium (Tensilon) testing, should be avoided during suspected myasthenic crisis 3