Myasthenia Gravis — SAQ · MBBS SAQ

Question

10 marks10 min

Stem

A 28-year-old woman with established AChR-antibody-positive generalised myasthenia gravis takes pyridostigmine and prednisolone. After two days of fever and productive cough, she develops rapidly worsening dysphagia, a fading voice, orthopnoea and difficulty clearing secretions. She is sitting upright, respiratory rate 28/min, using accessory muscles, with a weak cough and saliva pooling in the mouth. Oxygen saturation is 96% on room air. Her upright forced vital capacity (FVC) has fallen from 2.3 L to 1.4 L over six hours and her negative inspiratory force (NIF) from −38 to −24 cmH2O; a venous blood gas shows rising carbon dioxide. [2][3]

Question

Outline her management during the first 24 hours. Your answer must explain how you decide on ventilatory support, name the rapid immunomodulatory options, review possible precipitants and plan safe recovery. (10 marks)[1][2]

Model answer and exact marking scheme

1. Recognition and trigger — 1 mark

0.5 mark: Recognise a severe MG exacerbation with evolving myasthenic crisis. Crisis is respiratory failure from MG requiring non-invasive or invasive ventilatory support; neither an FVC nor NIF value alone defines it.[2][3]
0.5 mark: Identify likely infection while also checking aspiration, recent surgery, pregnancy/puerperium, missed treatment, steroid initiation/escalation and newly started medicines as contributors. Cholinergic crisis is rare; do not use a simplistic pupil or “wet/dry” table to diagnose it.[1][2]

2. Airway, serial respiratory and bulbar assessment — 2 marks

0.5 mark: Move to ICU/neurocritical care, call anaesthesia/critical care early, keep nil by mouth and assess ability to protect the airway, swallow safely and handle saliva/secretions.[2][3]
0.5 mark: Repeat FVC and NIF/MIP with the same technique and interpret the trajectory, recognizing that facial weakness can make spirometry unreliable and that a stable number does not guarantee safety.[2][3]
0.5 mark: Reassess cough strength, secretion clearance, respiratory rate, accessory-muscle use, orthopnoea, speech, fatigue and conscious state frequently; monitor oxygenation but remember that saturation can remain normal during hypoventilation.[2][3]
0.5 mark: Trend blood gas/carbon dioxide when hypoventilation is suspected and plan controlled elective intubation for an unsafe airway, worsening bulbar dysfunction or secretions, increasing work/exhaustion, rising carbon dioxide or failed monitored NIV. The falling FVC and less-negative NIF support concern but do not independently mandate intubation.[2][3]

3. Ventilation, secretions and aspiration — 1 mark

0.5 mark: NIV is a closely monitored trial only in a cooperative patient who can protect the airway and clear secretions, without severe bulbar failure, rapidly worsening gas exchange or immediate intubation need.[2][3]
0.5 mark: In this patient, pooling secretions, weak cough, bulbar deterioration and rising carbon dioxide make early invasive ventilation likely. If a non-depolarising neuromuscular blocker is essential, use a reduced titrated dose with quantitative monitoring and an expert reversal/extubation plan; MG patients are unusually sensitive. Succinylcholine response is unpredictable—MG is not a denervation disorder.[2]

4. Rapid immunomodulation — 2 marks

1 mark: Give intravenous immunoglobulin (IVIg), total 2 g/kg intravenously divided over 2–5 days, after assessing renal function, thrombosis/haemolysis risk and fluid status.[1][2]
1 mark: Or use therapeutic plasma exchange (PLEX), commonly 4–6 exchanges over about 1–2 weeks, considering vascular access, haemodynamic stability, sepsis and local expertise. PLEX is often chosen when a faster response is clinically important or in MuSK crisis, but access and haemodynamic complications matter. Both are accepted rescue options; the randomized comparison studied moderate-to-severe worsening, not a definitive crisis head-to-head trial. Do not combine routinely.[1][2][4]

5. Treat infection and review medicines — 1 mark

0.5 mark: Obtain cultures and chest imaging as indicated, treat pneumonia/aspiration promptly with an effective antibiotic guided by severity, local resistance and microbiology, and manage sepsis. Necessary infection treatment must not be delayed by an MG caution list.[2][3]
0.5 mark: Review recent drugs. Telithromycin, botulinum toxin and D-penicillamine should be avoided; D-penicillamine is strongly associated with causing MG. Fluoroquinolones have an FDA boxed warning, and aminoglycosides/macrolides can worsen transmission. Intravenous magnesium, beta-blockers, procainamide, quinine, neuromuscular blockers and modern iodinated contrast require context-specific risk-benefit review and monitoring. Necessary treatment should not be stopped without a safe alternative. The reader-visible MGFA cautionary-drugs list gives the same avoid/caution distinctions.[1][2]

6. Pyridostigmine and corticosteroid plan — 1 mark

0.5 mark: If she is intubated or secretions are marked, temporarily hold pyridostigmine to reduce secretion burden, then restart it during objective improvement and weaning; do not stop it categorically in every exacerbation.[1][2]
0.5 mark: Continue or adjust immunotherapy with neurology input. Starting or rapidly escalating corticosteroid can transiently worsen MG, especially bulbar/respiratory disease, so use monitored escalation and consider rescue therapy before or during the change rather than automatically giving high-dose steroid in the first hour.[1][2]

7. ICU supportive care — 1 mark

1 mark: Provide aspiration-safe enteral nutrition when appropriate, individualized VTE prophylaxis, pressure care, secretion management and chest physiotherapy; monitor glucose, electrolytes, renal function and complications of IVIg/PLEX/ventilation. Do not prescribe one fixed anticoagulant dose or routine stress-ulcer prophylaxis to every patient without weight, renal, bleeding and local-protocol assessment.[2][3]

8. Weaning, MDT and follow-up — 1 mark

1 mark: Coordinate neurology, ICU/respiratory medicine, anaesthesia, speech-language pathology, dietetics, physiotherapy/occupational therapy, pharmacy and—if aspiration pneumonia is present—microbiology. Extubate only after improving MG, adequate cough and secretion clearance, safer bulbar function, stable gas exchange and a successful spontaneous-breathing assessment, not because one FVC threshold is crossed. Before discharge, optimize long-term immunotherapy, review thymic-imaging status (without repeating it routinely), reconcile medicines/vaccines, provide an MG alert card and crisis plan, and arrange specialist follow-up with MG-ADL and adverse-effect monitoring.[1][2][3]

Mark total

1 + 2 + 1 + 2 + 1 + 1 + 1 + 1 = 10 marks exactly. Do not award an intubation mark merely for quoting “FVC below 20 mL/kg” or another isolated number; credit trajectory-led airway, bulbar and ventilatory reasoning.[2][3]

References

[1]Narayanaswami P, Sanders DB, Wolfe G, et al. International Consensus Guidance for Management of Myasthenia Gravis: 2020 Update Neurology, 2021.PMID 33144515
[2]Wiendl H, Abicht A, Chan A, et al. Guideline for the management of myasthenic syndromes Ther Adv Neurol Disord, 2023.PMID 38152089
[3]Wendell LC, Levine JM. Myasthenic crisis Neurohospitalist, 2011.PMID 23983833
[4]Barth D, Nabavi Nouri M, Ng E, et al. Comparison of IVIg and PLEX in patients with myasthenia gravis Neurology, 2011.PMID 21562253
[5]Rousseff RT. Diagnosis of Myasthenia Gravis J Clin Med, 2021.PMID 33923771

Question

10 marks10 min

Stem

Question

Model answer and exact marking scheme

1. Recognition and trigger — 1 mark

0.5 mark: Recognise a severe MG exacerbation with evolving myasthenic crisis. Crisis is respiratory failure from MG requiring non-invasive or invasive ventilatory support; neither an FVC nor NIF value alone defines it.[2][3]
0.5 mark: Identify likely infection while also checking aspiration, recent surgery, pregnancy/puerperium, missed treatment, steroid initiation/escalation and newly started medicines as contributors. Cholinergic crisis is rare; do not use a simplistic pupil or “wet/dry” table to diagnose it.[1][2]

2. Airway, serial respiratory and bulbar assessment — 2 marks

0.5 mark: Move to ICU/neurocritical care, call anaesthesia/critical care early, keep nil by mouth and assess ability to protect the airway, swallow safely and handle saliva/secretions.[2][3]
0.5 mark: Repeat FVC and NIF/MIP with the same technique and interpret the trajectory, recognizing that facial weakness can make spirometry unreliable and that a stable number does not guarantee safety.[2][3]
0.5 mark: Reassess cough strength, secretion clearance, respiratory rate, accessory-muscle use, orthopnoea, speech, fatigue and conscious state frequently; monitor oxygenation but remember that saturation can remain normal during hypoventilation.[2][3]
0.5 mark: Trend blood gas/carbon dioxide when hypoventilation is suspected and plan controlled elective intubation for an unsafe airway, worsening bulbar dysfunction or secretions, increasing work/exhaustion, rising carbon dioxide or failed monitored NIV. The falling FVC and less-negative NIF support concern but do not independently mandate intubation.[2][3]

3. Ventilation, secretions and aspiration — 1 mark

0.5 mark: NIV is a closely monitored trial only in a cooperative patient who can protect the airway and clear secretions, without severe bulbar failure, rapidly worsening gas exchange or immediate intubation need.[2][3]
0.5 mark: In this patient, pooling secretions, weak cough, bulbar deterioration and rising carbon dioxide make early invasive ventilation likely. If a non-depolarising neuromuscular blocker is essential, use a reduced titrated dose with quantitative monitoring and an expert reversal/extubation plan; MG patients are unusually sensitive. Succinylcholine response is unpredictable—MG is not a denervation disorder.[2]

4. Rapid immunomodulation — 2 marks

1 mark: Give intravenous immunoglobulin (IVIg), total 2 g/kg intravenously divided over 2–5 days, after assessing renal function, thrombosis/haemolysis risk and fluid status.[1][2]
1 mark: Or use therapeutic plasma exchange (PLEX), commonly 4–6 exchanges over about 1–2 weeks, considering vascular access, haemodynamic stability, sepsis and local expertise. PLEX is often chosen when a faster response is clinically important or in MuSK crisis, but access and haemodynamic complications matter. Both are accepted rescue options; the randomized comparison studied moderate-to-severe worsening, not a definitive crisis head-to-head trial. Do not combine routinely.[1][2][4]

5. Treat infection and review medicines — 1 mark

0.5 mark: Obtain cultures and chest imaging as indicated, treat pneumonia/aspiration promptly with an effective antibiotic guided by severity, local resistance and microbiology, and manage sepsis. Necessary infection treatment must not be delayed by an MG caution list.[2][3]
0.5 mark: Review recent drugs. Telithromycin, botulinum toxin and D-penicillamine should be avoided; D-penicillamine is strongly associated with causing MG. Fluoroquinolones have an FDA boxed warning, and aminoglycosides/macrolides can worsen transmission. Intravenous magnesium, beta-blockers, procainamide, quinine, neuromuscular blockers and modern iodinated contrast require context-specific risk-benefit review and monitoring. Necessary treatment should not be stopped without a safe alternative. The reader-visible MGFA cautionary-drugs list gives the same avoid/caution distinctions.[1][2]

6. Pyridostigmine and corticosteroid plan — 1 mark

0.5 mark: If she is intubated or secretions are marked, temporarily hold pyridostigmine to reduce secretion burden, then restart it during objective improvement and weaning; do not stop it categorically in every exacerbation.[1][2]
0.5 mark: Continue or adjust immunotherapy with neurology input. Starting or rapidly escalating corticosteroid can transiently worsen MG, especially bulbar/respiratory disease, so use monitored escalation and consider rescue therapy before or during the change rather than automatically giving high-dose steroid in the first hour.[1][2]

7. ICU supportive care — 1 mark

1 mark: Provide aspiration-safe enteral nutrition when appropriate, individualized VTE prophylaxis, pressure care, secretion management and chest physiotherapy; monitor glucose, electrolytes, renal function and complications of IVIg/PLEX/ventilation. Do not prescribe one fixed anticoagulant dose or routine stress-ulcer prophylaxis to every patient without weight, renal, bleeding and local-protocol assessment.[2][3]

8. Weaning, MDT and follow-up — 1 mark

1 mark: Coordinate neurology, ICU/respiratory medicine, anaesthesia, speech-language pathology, dietetics, physiotherapy/occupational therapy, pharmacy and—if aspiration pneumonia is present—microbiology. Extubate only after improving MG, adequate cough and secretion clearance, safer bulbar function, stable gas exchange and a successful spontaneous-breathing assessment, not because one FVC threshold is crossed. Before discharge, optimize long-term immunotherapy, review thymic-imaging status (without repeating it routinely), reconcile medicines/vaccines, provide an MG alert card and crisis plan, and arrange specialist follow-up with MG-ADL and adverse-effect monitoring.[1][2][3]

Mark total

References

[1]Narayanaswami P, Sanders DB, Wolfe G, et al. International Consensus Guidance for Management of Myasthenia Gravis: 2020 Update Neurology, 2021.PMID 33144515
[2]Wiendl H, Abicht A, Chan A, et al. Guideline for the management of myasthenic syndromes Ther Adv Neurol Disord, 2023.PMID 38152089
[3]Wendell LC, Levine JM. Myasthenic crisis Neurohospitalist, 2011.PMID 23983833
[4]Barth D, Nabavi Nouri M, Ng E, et al. Comparison of IVIg and PLEX in patients with myasthenia gravis Neurology, 2011.PMID 21562253
[5]Rousseff RT. Diagnosis of Myasthenia Gravis J Clin Med, 2021.PMID 33923771