Myasthenia Gravis Diagnosis Criteria

Myasthenia Gravis (MG) is an autoimmune disorder that affects the neuromuscular junction. The diagnostic criteria for Myasthenia Gravis are outlined below, based on clinical evaluation and supporting tests.

Clinical Presentation

Fluctuating muscle weakness is a hallmark of Myasthenia Gravis. Many patients experience weakness in the eye muscles, such as drooping eyelids (ptosis), and may also develop weakness in the limbs or respiratory muscles. This weakness typically fluctuates in severity — it may improve with rest and worsen after physical activity. A characteristic feature observed in clinical practice is the "waning strength throughout the day." Symptoms often appear milder in the morning upon waking and become more pronounced as the day progresses and physical activity increases.

Fatigue Test

During a fatigue test, patients are asked to perform repetitive movements. In individuals with MG, this type of sustained activity leads to a noticeable decline in muscle strength in the tested area. This test helps clinicians observe the fatigability of muscles, a key indicator of the disease.

Edrophonium (Tensilon) Test

The Edrophonium test, also known as the Tensilon test, is another diagnostic tool used in clinical settings. When a cholinesterase inhibitor like Edrophonium is administered, a temporary improvement in muscle strength is observed in MG patients. This positive response is referred to as a positive Edrophonium test and serves as a significant diagnostic marker.

Electrophysiological Studies

Repetitive Nerve Stimulation (RNS)

Electromyography (EMG) with repetitive nerve stimulation is a key diagnostic investigation. During this test, a decrease in the amplitude of the muscle action potential by 15% or more is considered significant and highly suggestive of Myasthenia Gravis. This electrophysiological finding supports the clinical diagnosis and helps differentiate MG from other neuromuscular disorders.