A 62-year-old man with a lung mass reports difficulty rising from a chair and climbing stairs. Examination shows proximal muscle weakness that improves after brief exertion, hyporeflexia, and ptosis. Antibodies against which target are most likely present?

• A Postsynaptic acetylcholine receptor
• B Presynaptic voltage-gated calcium channel ✓
• C Muscle specific kinase
• D Voltage-gated potassium channel

Explanation

This is Lambert-Eaton myasthenic syndrome, a paraneoplastic disorder most often associated with small cell lung carcinoma. Autoantibodies against presynaptic P/Q-type voltage-gated calcium channels reduce acetylcholine release, causing proximal weakness, hyporeflexia and autonomic symptoms. Improvement after brief exercise reflects facilitation, which distinguishes it from myasthenia gravis, where antibodies are postsynaptic against the acetylcholine receptor and fatigability worsens with use.

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.