Myasthenic Crisis versus Cholinergic Crisis versus Sepsis in a Ventilated Patient
A 34-year-old woman with known acetylcholine receptor antibody-positive myasthenia gravis on pyridostigmine 60 mg q6h and prednisone 10 mg daily presents with 2 days of worsening dysphagia and breathlessness. On arrival: BP 138/84, HR 104, RR 28, SpO2 92% on 2 L, temp 38.6 C, bilateral ptosis, nasal speech, weak cough, and paradoxical abdominal breathing. Chest X-ray shows a right lower lobe infiltrate. She is intubated for respiratory failure. Post-intubation: BP 88/50, HR 128, temp 38.9 C, and copious oral secretions. The team is unsure whether this is myasthenic crisis, cholinergic crisis from pyridostigmine, or sepsis, and asks about pyridostigmine, antibiotics, and IVIG versus plasma exchange.
1. Differentiate myasthenic crisis, cholinergic crisis, and septic shock here. What is the most likely diagnosis and what immediate pharmacology changes do you make?
Read the worked answer
Cholinergic crisis from pyridostigmine excess produces increased secretions, bradycardia, miosis, diarrhea, and fasciculations - here there is copious oral secretion and tachycardia/hypotension, but the picture is dominated by fever, lobar infiltrate, and shock, which points to sepsis-triggered myasthenic crisis (the most common precipitant of crisis is infection). True cholinergic crisis is rare at standard doses and would be suggested by SLUDGE symptoms plus worsening weakness after a dose; the exam wants you to recognize that infection is the driver and that the shock is distributive (septic) rather than cholinergic.
Immediate pharmacology:
- Hold pyridostigmine during the acute crisis while intubated - it increases secretions and does not treat the crisis; restart when respiratory status and secretions improve.
- Sepsis bundle: cultures, broad-spectrum antibiotics (avoid agents that worsen MG - see next answer), fluids, norepinephrine for MAP ≥65, source control.
- MG-specific therapy: IVIG (2 g/kg over 2–5 days) or plasma exchange (5 exchanges) - both are first-line for crisis; PLEX is often preferred for severe/rapid deterioration or if IVIG is unavailable/contraindicated. Start now; effect takes days.
- Steroids: continue prednisone; if giving high-dose IV steroids, monitor for transient worsening (start under cover of PLEX/IVIG).
- Supportive: lung-protective ventilation, VTE prophylaxis, nutrition, and monitor for aspiration.
2. Which antibiotics should be avoided, and how do you monitor for and manage the expected complications of the chosen immunotherapy?
Read the worked answer
Antibiotics to avoid/use cautiously in myasthenia gravis: aminoglycosides (gentamicin, tobramycin, amikacin), fluoroquinolones (ciprofloxacin, levofloxacin - black-box warning for MG exacerbation), macrolides (azithromycin, clarithromycin), and tetracyclines; also avoid magnesium-containing fluids and neuromuscular blockers. Safe choices include ceftriaxone, cefepime (watch for neurotoxicity in renal failure), piperacillin-tazobactam, vancomycin (monitor levels), and linezolid with caution. Choose based on the likely pathogen (community-acquired pneumonia: ceftriaxone + azithromycin is standard, but substitute doxycycline or a beta-lactam for the macrolide given MG).
Monitoring the immunotherapy:
- IVIG: check baseline IgA (IgA deficiency → anaphylaxis risk), renal function (avoid in renal failure; sucrose-containing products cause osmotic nephrosis), and monitor for thrombosis (DVT/PE, stroke, MI - especially with immobility and inflammation), aseptic meningitis, hemolysis (check CBC post-infusion), and volume overload. Do not co-administer with live vaccines.
- PLEX: requires central access (bleeding, infection, pneumothorax), monitor electrolytes (citrate → hypocalcemia, hypokalemia, hypomagnesemia), coagulation (fibrinogen, platelets), and hemodynamics; hold ACE inhibitors (bradykinin reactions) and adjust drug dosing for removal.
- General: serial vital capacity/negative inspiratory force (though intubated), daily sedation/sedation vacation, and a plan for extubation when VC >15–20 mL/kg and NIF more negative than -20 to -30 cm H2O, with close monitoring for recrudescence.