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.