Myasthenia Gravis Diagnostic Tests

Myasthenia Gravis (MG) is a chronic autoimmune neuromuscular disorder characterized by varying degrees of weakness in the skeletal muscles. To accurately diagnose this condition, a series of specific diagnostic tests are typically performed alongside a thorough evaluation of clinical symptoms.

Common Diagnostic Tests for Myasthenia Gravis

Muscle Fatigue Test

During a muscle fatigue test, a healthcare provider asks the patient to perform repetitive movements to assess muscle endurance. For example, the patient may be asked to look upward continuously for one minute to check for eyelid drooping. Alternatively, the patient may be instructed to blink repeatedly for 30 seconds to see if symptoms appear. Limb fatigue can also be tested by asking the patient to hold their arms outstretched for two minutes or perform 10–20 squats to evaluate for weakness or difficulty. A positive result occurs when these symptoms manifest during the test.

Edrophonium Test

The edrophonium test involves administering a short-acting anticholinesterase medication, such as neostigmine methylsulfate, via intramuscular injection. The response is monitored for about 30 minutes. If there is a noticeable improvement in muscle strength following the injection, the test is considered positive, supporting a diagnosis of Myasthenia Gravis.

Electromyography (EMG)

Electromyography is used to evaluate the electrical activity of muscles. In the context of MG diagnosis, repetitive nerve stimulation tests are performed at low frequencies. A decrement in muscle response of more than 10% during low-frequency stimulation is considered a positive finding, indicating impaired neuromuscular transmission.

Antibody Testing

Blood tests are often conducted to detect the presence of specific antibodies associated with Myasthenia Gravis. These typically include antibodies against acetylcholine receptors (AChR), muscle-specific kinase (MuSK), or lipoprotein-related protein 4 (LRP4). The detection of these autoantibodies supports the diagnosis of MG.

Chest CT Scan

A chest CT scan is performed to examine the thymus gland, which is located in the chest behind the breastbone. Approximately 70% of patients with Myasthenia Gravis have thymic abnormalities, such as thymic hyperplasia or thymoma. Identifying such abnormalities through imaging provides strong supportive evidence for the diagnosis of MG.

Importance of Clinical Evaluation

While these diagnostic tests are essential in confirming Myasthenia Gravis, the clinical presentation of the patient plays a crucial role in the diagnostic process. If a patient exhibits classic symptoms of MG and at least one of the above tests yields a positive result, a definitive diagnosis of Myasthenia Gravis can be made. Early and accurate diagnosis is key to initiating appropriate treatment and improving quality of life for individuals living with this condition.