Diagnosis is based on clinical features, tests for antibodies, Electromyography (EMG), nerve conduction studies, and clinical response to medications. A detailed history is taken and physical examination is performed.
- 85% of
patients with generalized symptoms have acetylcholine receptor antibodies. A blood test is performed to detect these abnormal antibodies
- 15% of patients do not test positive for acetylcholine receptor antibodies. Detection of muscle-specific
kinase antibodies (anti-MuSK antibodies) is done.
- Edrophonium (Tensilon) is a chemical which when injected into veins may transiently improve symptoms due to Myasthenia Gravis. This can hence be used as a test.
- Non specific tests: Electromyography (EMG) studies may reveal characteristic patterns. Single fibre EMG, repeated nerve stimulation, muscle biopsies are also performed.
These tests may be negative in patients even if they have myasthenia gravis.