Neuromuscular Medicine: Disease-Specific Recognition and Management
Know the classic presentations cold
- Guillain-Barre syndrome (AIDP): ascending symmetric weakness, areflexia, albuminocytologic dissociation (elevated CSF protein with normal cells), nadir within ~4 weeks. Treat with IVIG or plasma exchange; avoid corticosteroids as monotherapy. Watch for respiratory failure and dysautonomia.
- CIDP: relapsing or progressive over >8 weeks, areflexia, demyelinating NCS; responds to IVIG, steroids, or plasma exchange.
- Myasthenia gravis: ptosis, diplopia, bulbar and proximal weakness worsening with use; anti-AChR or anti-MuSK antibodies; treat with pyridostigmine, immunosuppression, thymectomy in selected cases. Lambert-Eaton is presynaptic, improves with exercise, associates with anti-VGCC antibodies and small-cell lung cancer.
- Inflammatory myopathies: dermatomyositis (Gottron papules, heliotrope rash, anti-Mi-2), polymyositis, immune-mediated necrotizing myopathy (anti-SRP/HMGCR).
- ALS: progressive mixed UMN/LMN weakness, bulbar onset in some, riluzole/edaravone are disease-modifying.
- Hereditary neuropathies: Charcot-Marie-Tooth type 1 is demyelinating (PMP22 duplication), type 2 is axonal; pes cavus, hammer toes, areflexia.
Traps
- Steroid-responsive confusion: steroids help CIDP but not GBS.
- Antibody-negative myasthenia still exists; do not exclude it on serology alone.
- Lambert-Eaton improves with sustained contraction, unlike MG fatigue.
- Missing respiratory compromise (vital capacity) in acute neuromuscular disease.
Worked example
A patient with diplopia and ptosis worse in the evening, normal pupils and reflexes, and a normal MRI: the fatigable pattern points to NMJ, and serology plus repetitive nerve stimulation confirm myasthenia gravis. Rule of thumb: fatigability plus normal sensation and reflexes equals NMJ until proven otherwise.