Lambert-Eaton myasthenic syndrome. Lambert-Eaton syndrome is a paraneoplastic disorder that manifests as muscular weakness, wasting, and fatigability of the proximal limbs and trunk. Also termed myasthenic-myopathic syndrome, the disease is usually associated with small cell carcinoma of the lung, although it may also occur in patients with other malignant diseases. Like myasthenia gravis, the disease seems to have an autoimmune basis because it can be transferred to mice by IgG from patients and it responds to treatment with corticosteroids. The pathogenic IgG autoantibodies recognize voltage-sensitive calcium channels that are expressed both in motor nerve terminals and in the cells of the lung cancer. The calcium channels, which are necessary for release of acetylcholine, are greatly reduced in the presynaptic membrane in these patients, thereby interfering with neuromuscular transmission. Antichannel antibodies are not encountered in the other choices.Diagnosis: Lambert-Eaton myasthenic syndrome