A 55-year-old man with small cell lung carcinoma develops bilateral proximal leg weakness worse with ambulation but improving with repetitive use. Deep tendon reflexes are absent. This paraneoplastic syndrome is caused by IgG antibodies targeting:
- A Acetylcholine receptors at the neuromuscular junction
- B Voltage-gated potassium channels causing hyperexcitability
- C Voltage-gated calcium channels (VGCC) at presynaptic terminals ✓
- D Muscle-specific kinase (MuSK)
Correct answer: C. Voltage-gated calcium channels (VGCC) at presynaptic terminals
Explanation
Lambert-Eaton myasthenic syndrome (LEMS) is caused by IgG antibodies against presynaptic voltage-gated calcium channels, impairing acetylcholine release. Paradoxically, repetitive stimulation temporarily increases calcium accumulation and improves strength (unlike myasthenia gravis, which worsens). SCLC tumor cells express VGCC, triggering the autoimmune response. AChR antibodies cause myasthenia gravis (worse with activity); MuSK antibodies are a variant of MG; VGKC antibodies cause limbic encephalitis.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.