A 62-year-old smoker with a biopsy proven small cell lung carcinoma develops proximal limb weakness that improves after brief sustained effort. Deep tendon reflexes are reduced. The underlying autoantibody targets which structure?

• A Postsynaptic acetylcholine receptor at the neuromuscular junction
• B Presynaptic voltage gated calcium channel ✓
• C Voltage gated potassium channel of peripheral nerve
• D Acetylcholine esterase enzyme at the synaptic cleft

Explanation

Lambert Eaton myasthenic syndrome results from IgG antibodies against presynaptic voltage gated calcium channels, reducing acetylcholine release. Repetitive activity raises intracellular calcium enough to improve transmission, hence the characteristic facilitation with sustained contraction, which distinguishes it from myasthenia gravis where postsynaptic acetylcholine receptors are targeted and strength fatigues further with use. Voltage gated potassium channel antibodies cause acquired neuromyotonia, not this syndrome.

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.