💪 Chapter 67: Acute Neuromuscular Disorders

Guillain-Barré syndrome (GBS) · Myasthenia gravis (MG) · Respiratory muscle weakness · Vital capacity monitoring · Intubation criteria (VC <20 mL/kg, Pi max <-30) · IVIG vs plasmapheresis · Myasthenic vs cholinergic crisis · Tensilon test · Thymectomy

🔍 Core Concepts: Acute Neuromuscular Disorders

📌 Guillain-Barré Syndrome (GBS)
Acute inflammatory demyelinating polyneuropathy. Ascending weakness, areflexia. CSF: albuminocytologic dissociation (high protein, normal cells). Respiratory failure risk. Treatment: IVIG 0.4 g/kg/day x 5 days or plasmapheresis.
💊 Myasthenia Gravis (MG)
Autoantibodies against acetylcholine receptors. Fatigable weakness, ptosis, diplopia, bulbar weakness. Edrophonium (Tensilon) test. Treatment: pyridostigmine, steroids, IVIG, plasmapheresis, thymectomy.
🫁 Respiratory Monitoring
Vital capacity (VC) <20 mL/kg, Pi max < -30 cmH2O, Pe max <40 cmH2O → high risk of respiratory failure. Single-breath count (<10) indicates VC ~15-20 mL/kg. Intubate if bulbar weakness, aspiration, rising PaCO2.
⚡ Myasthenic vs Cholinergic Crisis
Myasthenic: weakness, responds to edrophonium. Cholinergic: excessive pyridostigmine → weakness + muscarinic effects (salivation, miosis, diarrhoea). Treatment: withhold pyridostigmine, atropine.
🧪 Diagnosis
GBS: LP (elevated protein), EMG/NCS (demyelination). MG: anti-AChR antibodies, repetitive nerve stimulation (decrement >10%), edrophonium test.
🏥 ICU Management
Monitor VC Q4-6h. Early intubation for declining VC. Autonomic dysfunction in GBS (BP lability, arrhythmias). DVT prophylaxis. Pain management (neuropathic pain). Slow weaning, tracheostomy for prolonged ventilation.

🩺 Stepwise Approach: Acute Neuromuscular Disorders

1
Assess respiratory function
Measure vital capacity (VC), maximum inspiratory pressure (Pi max), maximum expiratory pressure (Pe max). Single-breath count (count to 20? 30?). VC <20 mL/kg or Pi max < -30 cmH2O → high risk of respiratory failure.
2
Bulbar function & airway protection
Assess speech, swallow, cough, gag reflex. Nasal speech, dysphagia, weak cough indicate bulbar involvement → high aspiration risk → consider intubation.
3
GBS-specific treatment
IVIG 0.4 g/kg/day x 5 days (within 2 weeks of onset) or plasmapheresis (5 exchanges). Steroids not effective. Monitor autonomic dysfunction (BP, HR).
4
Myasthenia gravis management
Pyridostigmine (0.5-1 mg/kg Q4-6h). Myasthenic crisis: IVIG or plasmapheresis, corticosteroids. Cholinergic crisis: withhold pyridostigmine, atropine. Thymectomy for AChR-positive generalised MG.
5
Intubation & ventilation
Indications: VC <15-20 mL/kg, Pi max < -25 to -30, hypercapnia, hypoxia, bulbar weakness. Use pressure support or SIMV. Avoid long-acting paralytics. Tracheostomy for prolonged ventilation (>2-3 weeks).
6
Supportive care
DVT prophylaxis (LMWH). Pain management (gabapentin, carbamazepine for neuropathic pain). Physiotherapy, bowel/bladder care. Slow weaning.