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Myasthenia Gravis &
Lambert-Eaton Syndrome

An algorithmic approach to expedite diagnosis and treatment

Autoantibody profiles aid the diagnosis of myasthenia gravis and Lambert-Eaton syndrome. However, characteristic clinical and electrophysiological features are also required for the diagnosis. Seronegativity does not exclude the diagnosis.


Our diagnostic algorithms consist of tests that are always performed, and then additional testing is performed depending on the initial results. The additional testing in that setting involves looking for other antibody markers, which would support a diagnosis of myasthenia gravis or thymoma.

Myasthenia Gravis

Characteristic findings are weakness and fatiguability that
are improved by rest or anticholinesterase medication.
EMG demonstrates decrement in compound muscle action
potential (CMAP) during repetitive-motor nerve stimulation. Chest CT or MRI may reveal thymic enlargement, thymoma, or thymic carcinoma.

Other neoplastic accompaniments other than thymoma include gynecological cancers, prostate cancer, breast
cancer, bladder cancer, and lung cancer

Lambert-Eaton Syndrome

Characteristic clinical findings include proximal weakness,
sometimes including craniofacial involvement. This can be improved by brief exercise. Limited dysautonomia is frequently encountered, and this can include dry mouth and eyes, impaired sweating, and erectile dysfunction. The EMG findings demonstrate baseline CMAP reduction and facilitation of the CMAP after brief exercise or high-frequency nerve stimulation.

Neoplastic accompaniments include small-cell lung carcinoma in about 90% of paraneoplastic cases

Which test should I order?

Learn more about how to order these evaluations at your institution.