Complete evidence-based clinical platform covering Anti-AChR / Anti-MuSK / Anti-LRP4 immunopathology, Cogan lid twitch, Curtain & Peek signs, Ice Pack & Edrophonium tests, 3 Hz RNS & SFEMG jitter simulator, formal MGFA diagnostic criteria, and weight-based dosing for Pyridostigmine, Corticosteroids, Azathioprine, PLEX/IVIG, Rituximab, FcRn Antagonists, and Complement C5 Inhibitors.
Cardinal Hallmark: Fluctuating, fatigable skeletal muscle weakness that worsens with repetitive activity / evening hours (diurnal variation) and improves with rest or cooling.
Select an antibody profile to inspect IgG subclass, synaptic mechanism, thymic pathology, thymectomy eligibility, and precision therapy rules.
Thymus Histology: Thymic follicular hyperplasia (~65% in early-onset <50 yr, female predominance) or Thymoma (~10–15%, peak age 40–60 yr, M=F).
Calculate weight-indexed Forced Vital Capacity (FVC in mL/kg), Negative Inspiratory Force (NIF/MIP), and Single-Breath Count to guide ICU intubation before hypoxic arrest.
Meets 20/30/40 Rule threshold for impending/active Myasthenic Crisis (MGFA Class IVb/V)! Transfer to Neuro-ICU immediately, perform elective endotracheal intubation BEFORE hypoxemia/acidosis occurs, HOLD oral/IV Pyridostigmine while intubated (to prevent bronchorrhea), and initiate urgent PLEX (5 exchanges) or IVIG (2 g/kg).
Any ocular muscle weakness (ptosis, diplopia). May have weakness of eye closure (orbicularis oculi). All other facial, bulbar, axial, and limb muscle strength is completely normal.
Mild weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity.
Moderate weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity.
Severe weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity.
Defined by intubation with or without mechanical ventilation, EXCEPT when employed during routine postoperative management. (Note: Non-invasive BiPAP used to avoid intubation in acute hypercapnic/hypoxic respiratory failure is clinically managed as Crisis).
| Parameter | Myasthenic Crisis (>95%) | Cholinergic Crisis (<5%) |
|---|---|---|
| Underlying Pathophysiology | SEVERE UNDER-ACTIVITY at NMJ: Disease exacerbation (infection, surgery, steroid dip, medication trigger, tapering immunosuppression) causing autoimmune failure of postsynaptic AChRs. | EXCESSIVE OVER-STIMULATION at NMJ: Overdose of Acetylcholinesterase Inhibitors (typically Pyridostigmine >480–600 mg/day or excess IV Neostigmine) causing persistent depolarization block of postsynaptic AChRs. |
| Clinical Incidence in ICU | >95–99% of all neuromuscular crises in MG patients (COMMON — affects 15–20% of MG patients at least once in their lifetime, usually within the first 2–3 years). | <1–5% (RARE in modern practice unless patient is self-escalating high-dose Mestinon >120 mg q2–3h). |
| Pupil Size & Reactivity | NORMAL or DILATED (mydriatic from sympathetic stress/hypoxia), briskly reactive to light. | PINPOINT MIOSIS (<2 mm constriction due to muscarinic M3 sphincter pupillae overstimulation). |
| Heart Rate & Hemodynamics | SINUS TACHYCARDIA & Hypertension (sympathetic surge secondary to respiratory distress and hypercapnia). | SINUS BRADYCARDIA, AV block, and Hypotension (vagal muscarinic M2 activation). |
| Secretions, GI & Autonomic ("SLUDGE") | Absent / Normal secretions (unless concurrent pneumonia); normal bowel sounds; warm/diaphoretic only from work of breathing. | MARKED SLUDGE SYNDROME: Copious bronchorrhea/sialorrhea (frothy airway secretions), severe abdominal cramping, explosive diarrhea, profuse sweating, lacrimation, bronchospasm/wheezing. |
| Muscle Fasciculations & Cramps | ABSENT (flaccid weakness without fasciculations, except occasionally in MuSK+ patients on normal doses of pyridostigmine). | PROMINENT DIFFUSE FASCICULATIONS (tongue, eyelids, calves) and painful skeletal muscle cramps. |
| Immediate ICU Action & Definitive Management | 1. Intubate if FVC <15–20 mL/kg or NIF worse than -20 to -30 cmH2O. 2. HOLD Pyridostigmine while intubated! 3. Start PLEX (5 sessions) or IVIG (2 g/kg) + Corticosteroids + Treat infection. | 1. Secure airway / Intubate if respiratory failure or severe bronchorrhea. 2. IMMEDIATELY STOP ALL AChE Inhibitors (Pyridostigmine/Neostigmine)! 3. Administer ATROPINE 0.4–2.0 mg IV q15–30min PRN to dry life-threatening bronchial secretions and reverse bradycardia. |
Mechanism: Aminoglycosides inhibit presynaptic voltage-gated Ca2+ influx (mimicking LEMS/Mg2+ block); Fluoroquinolones & Macrolides cause direct postsynaptic AChR channel blockade.
Safe Alternatives / Action: Penicillins (Amoxicillin-Clavulanate, Piperacillin-Tazobactam), Cephalosporins (Ceftriaxone, Cefepime, Cefazolin), Carbapenems (Meropenem), Vancomycin, Doxycycline (use with mild caution), Trimethoprim-Sulfamethoxazole (TMP-SMX), Nitrofurantoin.
Mechanism: Breaks peripheral T-cell self-tolerance, triggering fulminant de novo autoimmune MG or fatal flare of pre-existing MG, frequently presenting as the lethal "Triple M Syndrome" (Myasthenia Gravis + Necrotizing Myositis + Fulminant Myocarditis) within 2–6 weeks of cycle 1–2!
Safe Alternatives / Action: Immediately hold ICI, check Serum CK + Troponin I/T + ECG + Echocardiogram, admit to ICU, and treat aggressively with High-Dose IV Methylprednisolone (1–2 mg/kg or 1,000 mg/day) + PLEX/IVIG + Abatacept/Rituximab if myocarditis is present.
Mechanism: Mg2+ competitively blocks presynaptic P/Q-type Calcium channels, drastically arresting acetylcholine vesicle exocytosis AND reducing postsynaptic membrane excitability — can cause immediate apnea/quadriplegia within minutes!
Safe Alternatives / Action: Avoid IV MgSO4 unless life-saving (e.g., Torsades de Pointes). In preeclampsia with MG, use Levetiracetam or Labetalol/Hydralazine/Nicardipine cautiously; if MgSO4 causes paralysis, reverse immediately with IV Calcium Gluconate 1–2 g!
Mechanism: EXTREME SENSITIVITY to Non-Depolarizing blockers (Rocuronium/Vecuronium): Because MG patients have ~70% fewer functional AChRs, even 10–20% of a standard dose can cause prolonged complete paralysis! Conversely, MG patients are relatively RESISTANT to Succinylcholine (requires ~1.5–2x dose to depolarize the reduced receptors, but risks prolonged Phase II block if pyridostigmine inhibits pseudocholinesterase).
Safe Alternatives / Action: Use Total Intravenous Anesthesia (TIVA with Propofol + Remifentanil) without NMBAs if possible. If paralysis is required, use reduced-dose Rocuronium (0.2–0.3 mg/kg) guided by quantitative Train-of-Four (TOF) monitoring and reverse completely with SUGAMMADEX (2–4 mg/kg IV)!
Mechanism: Procainamide/Quinine block postsynaptic AChR channels and reduce presynaptic ACh synthesis; CCBs impair presynaptic Ca2+ entry; Beta-blockers impair neuromuscular transmission efficiency (even Timolol glaucoma drops can unmask ocular ptosis/diplopia!).
Safe Alternatives / Action: ACE Inhibitors (Lisinopril, Enalapril — note: hold 24h prior to PLEX), ARBs (Losartan, Valsartan), Thiazide/Loop Diuretics (monitor K+ so hypokalemia does not worsen weakness), Amiodarone (if antiarrhythmic needed).
Mechanism: D-Penicillamine modifies MHC/AChR epitopes triggering true autoantibodies (resolves 6–12 months after stopping drug); Botulinum toxin cleaves presynaptic SNAP-25.
Safe Alternatives / Action: Use Trientine or Zinc instead of D-Penicillamine for Wilson disease; strictly avoid cosmetic Botox in MG patients.