Neurology - Lambert Eaton Myasthenic Syndrome Flashcards
(9 cards)
What is Lambert-Eaton myasthenic syndrome?
Autoimmune condition affecting the neuromuscular junction
What is Lambert-Eaton myasthenic syndrome associated with?
Small-cell lung cancer (SCLC)
Can occur as a primary autoimmune disorder without SCLC
What causes Lambert-Eaton myasthenic syndrome at the physiological level?
Antibodies against voltage-gated calcium channels
Antibodies can be produced in response to SCLC that express voltage-gated calcium channels
These antibodies then target voltage-gated calcium channels in the presynaptic membrane of the NMJ
What is the role of voltage-gated calcium channels in muscle contraction?
Release of ACh into the synapse of the neuromuscular junction
If voltage-gated calcium channels are destroyed, less ACh in the synapse causing a weaker signal and reduced muscle contraction
What are the key presenting features of Lambert-Eaton myasthenic syndrome?
- Proximal muscle weakness - difficulty climbing stairs, standing or raising arms
- Autonomic dysfunction - dry mouth, blurred vision, impotence and dizziness
- Reduced or absent tendon reflexes
How do signs and symptoms improve in Lambert-Eaton myasthenic syndrome?
Improve after periods of muscle contraction
Opposite to MG
Can have absent reflexes in resting patient
What is the management focus for Lambert-Eaton myasthenic syndrome?
Excluding underlying malignancy, such as small-cell lung cancer
What is the mechanism of action of Amifampridine?
Blocks voltage-gated potassium channels in the presynaptic membrane, prolonging depolarisation and assisting calcium channels
What are some treatment options for Lambert-Eaton myasthenic syndrome?
- Pyridostigmine (cholinesterase inhibitor)
- Immunosuppressants (e.g., prednisolone or azathioprine)
- IV immunoglobulins
- Plasmapheresis
