Myasthenia Gravis: autoimmune – directed against post-synaptic NM junction; look for bulbar muscle involvement that gets worse with activity.

Sign/Symptoms:

1. Ocular: ptosis/diplopia, EOM involvement, no pupillary involvement
2. Bulbar: dysarthria, dysphagia, fatigue with chewing
3. Weakness: proximal limb weakness, facial/neck weakness
4. Respiratory muscle weakness ⇒ Myasthenia crisis

Tests:

Bedside

• Ice-pack test – improved ptosis with ice pack administration
• Tensilon (edraphnium) – acetylchoinesterase inhibitor with rapid onset/short duration; NOT SPECIFIC

Serologic

• Acetylecholine receptor antibody
• Muscle specific tyrosine kinase antibody (Anti-MUSK)

Electrophysiologic

• Repetitive nerve stimulation: ↓ amplitude with repetitive stimulation ~75% have thymic abnormalities (85% thymic hyperplasia, 15% thymoma)

GBS: ascending motor and sensory involvement, symmetric

Timing: <4 weeks

Pathophysiology: Due to molecular mimicry → immune response to preceding infection cross reacts to peripheral nerve

Common trigger: Campylobacter Jejuni (most common), CMV, EBV, HIV, VZV, mycoplasma, Zika

Physical Exam:

• Absent/depressed DTRs (90%)
• Ascending weakness (~90%)
• Paresthesias (80%)
• Facial weakness/bulbar signs (55%)

LP: Albumino-cytologic dissociation

Miller Fisher Variant

• Ophthalmoplegia
• Ataxia
• Areflexia

Botulism: bulbar involvement – spread in craniocaudal direction ~ “descending paralysis” with CN/eye involvement