4.08 Myasthenia Gravis and Lambert Eaton Syndrome
MSK/Rheumatology review for the USMLE Step 1 Exam
- Introduction:
- Review of neuromuscular junction and its components: presynaptic part, postsynaptic part, synaptic cleft.
- Cascade of events leading to the release of acetylcholine into the synaptic cleft.
- Myasthenia Gravis:
- Autoimmune neuromuscular junction disease.
- Fluctuating muscle weakness, especially ocular and eyelid weakness, distal limb weakness.
- Antibodies target nicotinic acetylcholine receptors (n-AChR's).
- Association with thymic hyperplasia and enlarged thymus.
- Treatment: Acetylcholinesterase inhibitors (AChE inhibitors), immunosuppressants.
- Lambert Eaton Syndrome:
- Autoimmune neuromuscular junction disease associated with cancer.
- Fluctuating muscle weakness, autonomic dysfunction, decreased reflexes.
- Antibodies target presynaptic calcium channels on nerve terminals.
- Autonomic manifestations due to calcium channels also present in smooth muscle.
- Around 50% of cases associated with an underlying malignancy.
- Treatment: Immunosuppression, addressing underlying malignancy if present.
