Assessment of Breathing in Patients with Myasthenia Gravis

Initial Assessment Parameters

Measure negative inspiratory force (NIF) and vital capacity (VC) as baseline parameters in all myasthenia gravis patients, regardless of symptom severity 1
Apply the "20/30/40 rule" to identify patients at risk of respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 1
Perform complete sensorimotor examination with attention to variable strabismus, ptosis, and slow saccades that may indicate generalized weakness affecting respiratory muscles 2
Assess for clinical signs of respiratory fatigue including difficulty holding up the head, slurred speech, and trouble with chewing or swallowing 2

Conduct frequent pulmonary function assessments with NIF and VC measurements in patients with moderate to severe generalized weakness (MGFA class III-V) 1
Monitor respiratory function regularly even when patients don't show clinical signs of dyspnea, as respiratory insufficiency may develop without obvious symptoms 1

Consider the increased sensitivity to non-depolarizing neuromuscular blocking agents when assessing breathing in myasthenic patients who require anesthesia 3

Watch for signs of impending myasthenic crisis requiring ICU-level monitoring and immediate intervention 1
Immediately discontinue medications that can worsen myasthenia gravis and precipitate respiratory failure, including beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 1

Consider the ice test (application of ice pack over closed eyes) which may temporarily improve muscle strength, including respiratory muscles 2
Check for acetylcholine receptor antibodies, anti-MuSK antibodies, and LRP4 antibodies to confirm diagnosis in patients presenting with respiratory symptoms 1
Perform single-fiber electromyography, which is considered the gold standard for diagnosis in many centers and is positive in over 90% of patients with ocular myasthenia 2