Myasthenia Gravis Diagnosis: Understanding Symptoms and Testing Methods

Diagnosing myasthenia gravis (MG) primarily relies on clinical evaluation, including a thorough review of the patient's medical history and physical examination. One of the most characteristic signs of this condition is symmetrical muscle weakness, particularly affecting the proximal muscles closer to the body's core. Patients often experience abnormal fatigue, which differs from normal post-exercise tiredness in that it occurs after minimal exertion and lasts disproportionately longer than the activity itself.

Key Clinical Features

A hallmark symptom of myasthenia gravis is fluctuating muscle weakness that tends to worsen as the day progresses—a pattern often described as "better in the morning, worse in the evening." This pattern can also be triggered by physical activity, with symptoms rapidly intensifying after movement and improving with rest. For example, patients may experience drooping eyelids (ptosis) after repeated blinking, which can be assessed during a clinical examination.

Diagnostic Testing and Procedures

While clinical signs are crucial, diagnostic confirmation often requires additional testing. One of the earliest assessments is the edrophonium (Tensilon) test, which involves administering the drug after inducing muscle fatigue through repetitive movement. If the patient experiences rapid improvement in muscle strength within 15–20 minutes, this is considered a positive result, supporting the diagnosis of MG.

Imaging studies such as computed tomography (CT) or magnetic resonance imaging (MRI) are also commonly used to evaluate the thymus gland. Abnormalities such as thymic hyperplasia or thymoma are frequently associated with myasthenia gravis and can provide important diagnostic clues.

Electrophysiological Testing

Electromyography (EMG) plays a vital role in confirming the diagnosis. Repetitive nerve stimulation (RNS) tests can demonstrate a decremental response in muscle action potentials—typically a drop of more than 10% during low-frequency stimulation. Another highly sensitive technique is single-fiber EMG (SFEMG), which detects increased jitter between muscle fibers. This method can identify early or subtle neuromuscular transmission defects even before typical symptoms appear, although it requires specialized equipment and experienced technicians.

Antibody Testing for Confirmation

The gold standard for confirming myasthenia gravis is the detection of acetylcholine receptor (AChR) antibodies in the blood. Approximately 80–90% of patients with generalized MG test positive for these antibodies, while about 50–60% of those with ocular MG show a positive result. With advancements in laboratory technology, antibody testing has become more accessible and reliable, making it a cornerstone of modern MG diagnosis.