Eaton-Lambert Myasthenic Syndrome

• A rare autoimmune neuromuscular disorder
• Affecting the neuromuscular junction
• Usually associated with malignancy

• Proximal limb weakness
• Can also have bulbar and ocular symptoms, but less common
• Weakness improves with repeated activity (opposite of myasthenia)
• Lambert's sign = improved power with repeated hand grip
• Deep tendon reflexes are often reduced or absent.

There's often autonomic involvement too:

• Dry eyes
• Dry mouth
• Constipation
• Blurred vision
• Slow gastric transit
• Postural hypotension

• IgG antibodies agains the pre-synaptic voltage gated calcium channels at the neuromuscular junction*
• Reduces calcium entry with each action potential
• This means less acetylcholine is released with each action potential
• This causes reduced muscle activity and weakness
• Repeated stimulation allows more calcium in, and increases force of contraction

*Meanwhile in MG, autoantibodies are raised against either the acetylcholine receptor itself or muscle specific kinase

• Supportive management - ABC as per any disease ever
• 3,4-diaminopyridine (amifampridine) enhances ACh release by prolonging depolarisation
• Pyridostigmine (AChE inhibitor) not as useful as in myasthenia gravis

Eaton-Lambert

• Proximal limbs
• Power improves with repeated action
• Most patients have autonomic symptoms

Myasthenia Gravis

• Usually eyes and face affected
• Commonly bulbar as well
• Fatiguable weakness, worsens with repeated action
• Generally no autonomic involvement

• Small cell lung carcinoma

Rare:

• Non-small cell lung cancer
• Thymoma (malignant)
• Breast
• Gallbladder
• Prostate
• Bladder
• Stomach

• Delayed gastric emptying - high aspiration risk, use RSI
• Autonomic instability - cardiovascular support, arterial line
• Sensitivity to both depolarising and non-depolarising neuromuscular blocking agents - reduce dose significantly, neostigmine is safe to use
• Weakness - may need post op ventilation