A 58-year-old heavy smoker develops progressive difficulty rising from a chair and climbing stairs over 3 weeks. On examination, proximal limb weakness improves after sustained effort, deep tendon reflexes are reduced, and oculobulbar muscles are spared. The autoantibody implicated targets:

• A Postsynaptic acetylcholine receptors
• B Muscle-specific kinase (MuSK)
• C Voltage-gated potassium channels
• D Presynaptic voltage-gated calcium channels ✓

Explanation

Lambert-Eaton myasthenic syndrome is a paraneoplastic disorder, most often associated with small cell lung carcinoma. Antibodies against presynaptic voltage-gated calcium channels reduce acetylcholine release at the neuromuscular junction. Facilitation, where strength briefly improves with repeated use, and hyporeflexia distinguish it from myasthenia gravis, which involves postsynaptic ACh receptor antibodies, worsens with use, and typically affects ocular muscles first.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.