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Key Features

  • There is defective release of acetylcholine in response to a nerve impulse, leading to weakness, especially of the proximal muscles of the limbs

  • May be associated with small-cell carcinoma, sometimes developing before the tumor is diagnosed, and occasionally occurs with certain autoimmune diseases (eTable 39–1)

eTable 39–1.Paraneoplastic syndromes associated with cancer.

Clinical Findings

  • Variable weakness, typically improving with activity

  • Dysautonomic symptoms may also be present

  • A history of malignant disease may be obtained

  • Unlike myasthenia gravis, power steadily increases with sustained contraction


  • Electrophysiologic diagnosis: the muscle response to stimulation of its motor nerve increases remarkably after exercise or if the nerve is stimulated repetitively at high rates (50 Hz), even in muscles that are ...

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