Which test is used to support the diagnosis of myasthenia gravis?

Which test is used to support the diagnosis of myasthenia gravis?

• A. MRI brain
• B. Nerve conduction studies
• C. Serology for acetylcholine receptor antibodies
• D. ECG

Answer: (C)

Myasthenia gravis is an autoimmune disorder where antibodies attack the postsynaptic acetylcholine receptors at the neuromuscular junction, leading to fatigable weakness. Testing for acetylcholine receptor antibodies serves as a direct immunologic marker of this disease, making it the strongest single test to support the diagnosis. In most people with generalized MG, these antibodies are present, so their detection in the blood provides a highly specific indication that aligns with the clinical picture. This positivity helps confirm MG and also prompts evaluation for thymic abnormalities that often accompany the condition. Other tests mentioned aren’t as definitive for confirming MG. An MRI of the brain looks for central nervous system pathology and won’t confirm MG. Nerve conduction studies can show a characteristic decremental response at the neuromuscular junction and can support the diagnosis, but they don’t provide the direct autoimmune evidence that antibody testing offers. ECG isn’t used to diagnose MG. It’s also worth noting that a minority of MG patients may be seronegative or have different antibodies (like MuSK), so a negative acetylcholine receptor antibody test doesn’t completely rule out MG and may prompt additional testing.

Myasthenia gravis is an autoimmune disorder where antibodies attack the postsynaptic acetylcholine receptors at the neuromuscular junction, leading to fatigable weakness. Testing for acetylcholine receptor antibodies serves as a direct immunologic marker of this disease, making it the strongest single test to support the diagnosis. In most people with generalized MG, these antibodies are present, so their detection in the blood provides a highly specific indication that aligns with the clinical picture. This positivity helps confirm MG and also prompts evaluation for thymic abnormalities that often accompany the condition.

Other tests mentioned aren’t as definitive for confirming MG. An MRI of the brain looks for central nervous system pathology and won’t confirm MG. Nerve conduction studies can show a characteristic decremental response at the neuromuscular junction and can support the diagnosis, but they don’t provide the direct autoimmune evidence that antibody testing offers. ECG isn’t used to diagnose MG. It’s also worth noting that a minority of MG patients may be seronegative or have different antibodies (like MuSK), so a negative acetylcholine receptor antibody test doesn’t completely rule out MG and may prompt additional testing.