What Is an EMG Test Used to Diagnose?
- Dr. Matt Johnson
- September 25, 2025
Many people call us after feeling strange symptoms like tingling in a hand, sudden weakness in a leg, or numb spots that won’t go away. It’s natural to wonder what’s behind those sensations and whether an EMG test can really give you answers.
At Neuromuscular Diagnostics, we’ve seen patients who were surprised by how much clarity this test provides. In this post, we’ll walk you through what an EMG actually tests, what kinds of conditions it can detect, and how it fits into the bigger picture of diagnostic care.
What Is an EMG Test?
An EMG measures how your muscles respond to signals from your nerves. A fine needle electrode is placed in a muscle, and it records the electrical activity when the muscle is at rest and when it contracts.
If there is damage to the nerve or the muscle, the electrical signals look different. This helps doctors figure out whether your symptoms are caused by a nerve problem, a muscle problem, or both.
In many cases, an EMG is done alongside a nerve conduction study (NCV test). The NCV measures how quickly electrical signals travel through your nerves. MedlinePlus provides a clear overview of how EMG and NCV work together.
At Neuromuscular Diagnostics, we specialize in EMG and NCV testing. If you are looking for an EMG testing clinic in Chicago, our team provides expert, accurate testing in a comfortable setting.
What Is an EMG Test Used to Diagnose?
Doctors order EMG tests to find the root cause of symptoms such as:
Persistent tingling or numbness
Unexplained muscle weakness
Pain that radiates down the arm or leg
Muscle twitching or cramping
The test helps answer an important question: are the symptoms coming from the nerves, the muscles, or another source? The Cleveland Clinic explains how EMG testing provides this clarity.
Common Conditions an EMG Can Diagnose
1. Carpal Tunnel Syndrome
Carpal tunnel happens when the median nerve is compressed at the wrist. Patients often feel tingling or numbness in the fingers, especially at night. EMG confirms whether the nerve is being affected and how severe the compression is.
2. Radiculopathy (Pinched Nerves in Spine)
A pinched nerve in the neck or lower back can cause pain that radiates into the arm or leg. Conditions like herniated discs and sciatica fall into this category. EMG testing shows if the nerve root is damaged and helps doctors measure how much function is affected.
3. Peripheral Neuropathy
Peripheral neuropathy is common in people with diabetes or long-term alcohol use. It causes burning, tingling, or loss of sensation in the hands and feet. EMG can confirm nerve damage and help track how advanced the condition is.
4. Muscle Disorders (Myopathy, Dystrophy)
Sometimes muscle weakness is caused by the muscle itself rather than the nerve. EMG can detect muscle diseases such as myopathies or muscular dystrophy by showing abnormal electrical activity in the muscle tissue.
5. Nerve Compression or Injury
Injuries from accidents, surgery, or repetitive stress can damage nerves. EMG testing helps identify whether the nerve is healing properly or if long-term damage is present.
6. Neuromuscular Diseases (ALS and Others)
Though less common, EMG is a key tool in diagnosing serious neuromuscular conditions such as ALS. While not the only test used, it provides important evidence for specialists.
Can an EMG Test Diagnose All Nerve Problems?
It is important to know that EMG does not replace imaging tests like MRI or CT scans. Instead, EMG focuses on function — how well nerves and muscles are working together. In some cases, doctors may also recommend SSEP testing to evaluate sensory pathways in the spinal cord and brain, providing additional insight beyond what EMG alone can show — a service we also perform at our Chicago clinic.
For example, an MRI might show a disc pressing on a nerve in the spine, while EMG can show if that pressure is actually stopping the nerve from working correctly.
This makes EMG a powerful complement to other diagnostic tools. If you’re also wondering about the test experience itself, read our article: Does an EMG test hurt?
Why Doctors Recommend EMG Testing
Doctors recommend EMG because it:
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Helps find the exact cause of symptoms.
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Distinguishes between nerve and muscle disorders.
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Provides clear data to guide treatment plans.
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Detects conditions early before they worsen.
Patients often ask about how much an EMG test costs before scheduling. Understanding pricing is part of feeling prepared, and it helps reduce stress before the appointment. If you’re not sure whether you need this test, read our guide on the signs you may need EMG testing.
Final Thoughts: What Can EMG Testing Tell You?
So, what can an EMG diagnose? The test is used to detect conditions like carpal tunnel, sciatica, neuropathy, muscle disease, and nerve injury. It shows whether symptoms are coming from nerve or muscle problems, and it provides answers that imaging alone cannot.
If you are dealing with numbness, weakness, or unexplained pain, don’t wait for symptoms to get worse. An EMG test can help you and your doctor find the right path forward.
Schedule your EMG or NCV test with Neuromuscular Diagnostics today and get the answers you need.
Matt Johnson, PT, DPT is the founder of Neuromuscular Diagnostics in Chicago. As one of the few licensed physical therapists in Illinois trained in advanced electrodiagnostic techniques, Dr. Johnson specializes in EMG and Nerve Conduction Velocity (NCV) testing. His clinical focus is on accurately identifying neuromuscular disorders to support effective treatment planning and improve patient outcomes.
