Types of Autoimmune MG Diagnostic Tests Prognosis
Types of Autoimmune MG
Ocular myasthenia gravis is a form of MG in which the muscles that move the eyes and control the eyelids are easily fatigued and weakened. Common symptoms include double vision, drooping eyelids and/or eye closure. Approximately 15% of people with MG have ocular problems only. Ocular symptoms are often the first symptoms of MG, and many people may develop other generalized muscle weakness issues later on. In approximately 50% of people diagnosed with ocular myasthenia gravis, autoantibodies against acetylcholine receptors (AChR) can be detected with a blood test.
Generalized myasthenia gravis is a form of MG in which muscles outside eyes become weakened. Symptoms may include: droopy eyelids and/ or double vision, difficulty speaking, difficulty breathing, problems chewing and swallowing or trouble performing everyday tasks and generalized muscle weakness. Approximately 85% of people diagnosed with MG have AChR autoantibodies present in their blood tests.
For people with generalized MG, some will not have AChR antibodies present in the blood, but a small percentage will test positive for anti-MuSK (muscle-specific kinase) antibodies. In very rare cases, both AChR and MuSK antibodies can be detected. Approximately 6% of people with MG will test positive for MuSK antibodies, and most patients who are positive for MuSK antibodies suffer the generalized form of myasthenia gravis.
The presence and type of antibody present in blood can help guide treatment choices for people with MG. People with anti-MuSK antibodies may respond differently to medications than people with AChR antibodies.
Seronegative myasthenia gravis is a form of MG where autoantibodies (anti-AChR and anti-MuSK autoantibodies) are not detectable in the blood. Symptoms and response to treatments are often the same as those with AChR and MuSK antibodies. As autoantibodies are undetectable in the blood, resulting in negative test results, additional specialized diagnostic testing may be required to confirm an MG diagnosis. Approximately 10% of people with MG are considered seronegative. Sometimes, antibodies for other proteins such as agrin or LRP4 antibodies are present, signaling that these autoantibodies may be biomarkers of MG. As newer antibodies are discovered for MG, less number of patients are likely to be classified as seronegative.
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In addition to a complete medical and neurological evaluation, a number of tests may be used to establish an MG diagnosis, starting with the clinical exam. To examine for weakness with activity, a clinician may have a patient do a sustained task, like looking upwards to see if the eyelids begin to droop. To test for muscle weakness, a clinician may ask you to do exercises with certain muscles repeatedly and observe your ability to recover and recuperate strength to see if it improves after rest.
A diagnosis of MG is confirmed via several methods, including the following:
- Acetylcholine receptor (AChR) antibody testing- Blood test to detect abnormal antibodies. Approximately 85% of people diagnosed with MG test positive for this group of antibodies.
- Anti-MuSK antibody testing—Blood test for MG patients who have tested negative for the acetylcholine antibody (AChR). Approximately 6% of MG patients without AChR antibodies test positive for the anti-MUSK antibody.
- Ice Pack tests—Ice Pack tests are examinations performed by specialists to evaluate strength and recovery responses that could be consistent with an MG diagnosis.
- Edrophonium test- Edrophonium is a drug that prevents the breakdown of acetylcholine, allowing the clinician to understand your muscle response and whether the results are consistent with an MG diagnosis.
- Electromyography (EMG)— Repetitive nerve stimulations (RNS) applying electrical shocks are often used to gauge muscle response and action potential and whether results are consistent with an MG diagnosis
- Single-fiber electromyography (SFEMG)—Detects neuromuscular transmission defects by recording action potentials from individual muscle fibers using a small needle electrode.
Results from some of these tests can be negative or inconclusive, even for someone who may exhibit symptoms of MG. A clinician skilled in recognizing and distinguishing MG from other conditions is important in determining a proper diagnosis.
The outlook for most people with MG is positive, as current treatment options are often effective. While existing treatments do not cure MG, most patients have improved muscle strength and some even experience remission. New advances in research and clinical trials are helping us understand more about MG every day. We are committed to drive and support research towards a better understanding and a cure for MG. To learn more about our commitment to research, see here.