A 58-year-old man with small cell carcinoma of the lung develops proximal muscle weakness and absent deep tendon reflexes that improve with exercise. Immunofluorescence shows antibodies against presynaptic voltage-gated calcium channels. This paraneoplastic syndrome is best classified as:
- A Myasthenia gravis
- B Lambert-Eaton myasthenic syndrome ✓
- C Dermatomyositis
- D Eaton-Lambert antibody-negative syndrome
Correct answer: B. Lambert-Eaton myasthenic syndrome
Explanation
Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic disorder most commonly associated with small cell lung carcinoma, characterised by antibodies against presynaptic P/Q-type voltage-gated calcium channels that impair acetylcholine release. Unlike myasthenia gravis (postsynaptic), LEMS shows proximal weakness that paradoxically improves with repeated effort (post-tetanic facilitation) and absent or reduced tendon reflexes. Dermatomyositis is an inflammatory myopathy with a different mechanism and skin findings.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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