Myasthenia Gravis Diagnosis: Key Indicators and Testing Methods

Myasthenia Gravis (MG) is an autoimmune disorder characterized by dysfunction of acetylcholine receptors at the neuromuscular junction. The diagnostic process for this condition typically begins with a thorough review of the patient's medical history and clinical symptoms. Common indicators include fluctuating muscle weakness, a pattern of improvement in the morning and worsening in the evening, and increased fatigue following physical activity.

Initial Diagnostic Considerations

When these symptoms are present, healthcare providers should consider MG as a potential diagnosis. At this stage, targeted laboratory tests are essential. Blood tests are performed to detect specific antibodies associated with the disease, including acetylcholine receptor (AChR) antibodies, muscle-specific kinase (MuSK) antibodies, lipoprotein-related protein 4 (LRP4) antibodies, and R90 antibodies. These markers are highly specific and can offer direct diagnostic value.

Supporting Diagnostic Tools

In addition to antibody testing, thyroid function and rheumatologic antibody panels are often included in the initial workup, as autoimmune conditions frequently coexist. Another helpful diagnostic tool is the edrophonium (Tensilon) test. This involves administering a drug that temporarily improves muscle strength—typically within 20 to 60 minutes—providing a clear indication of MG if a noticeable improvement occurs.

Electrophysiological Assessments

Electrophysiological studies are also crucial in confirming the diagnosis. Repetitive nerve stimulation (RNS) testing may reveal a characteristic decrement in muscle response during low-frequency stimulation. Additionally, single-fiber electromyography (SFEMG) is a highly sensitive test that can detect impaired neuromuscular transmission, further supporting the diagnosis of MG.

Imaging and Long-Term Monitoring

It's also important to evaluate for associated conditions, particularly thymic abnormalities. Approximately 10–15% of MG patients have a thymoma, and many others may exhibit thymic hyperplasia. Therefore, a chest CT scan is recommended to assess the thymus gland. If initial imaging is normal, follow-up scans should be considered annually, as thymic changes may develop over time.