Investigations

There is an established series of tests for diagnosing myasthenia gravis:

• diagnosis can be confirmed by observing an improvement in strength after administering a short-acting anticholinesterase drug, for example, edrophonium chloride.
• electromyography may reveal that repetitive supramaximal nerve stimulation at low frequencies (3Hz) causes an abnormal decrement of the compound muscle potential due to blocking of transmission to individual muscle fibres
• in approximately 75% of patients with ocular symptoms, acetylcholine receptor antibodies are present. These are present in approximately 90% of patients with generalised disease
• a mediastinal computerise tomographic or magnetic resonance scan is required to detect a thymoma

N.B. anti-striated muscle antibody is associated with an increased risk of thymoma.

Reference

1. Narayanaswami P, Sanders DB, Wolfe G, et al. International consensus guidance for management of myasthenia gravis: 2020 update. Neurology. 2021 Jan 19;96(3):114-22.