Electrodiagnostic testing (EMG and nerve conduction studies) can play in important role in the correct diagnosis of work-related injuries. Pain, numbness, or weakness are common presenting symptoms in the injured worker. A timely and accurate diagnosis for the cause of these symptoms can lead to an appropriate treatment plan and reduce lost time from work. So how can an EMG help accomplish this?
What can an EMG do for you?
- Confirm the diagnosis
- Exclude other diagnoses
- Localize the lesion
- Determine the severity
- Define the pathophysiology (what part of the nerve is affected)
- Provide prognostic information
- Detect sub-clinical disease
Electrodiagnostic testing is up to 95 percent sensitive in detecting peripheral nerve compression, such as carpal tunnel syndrome. A negative EMG can essentially rule out this diagnosis. For cervical or lumbar radiculopathy, the sensitivity is less and can range from 50 to 70 percent. Other common diagnoses made on EMG include post-traumatic nerve injuries, cubital tunnel syndrome, and brachial plexopathies. Non-work related pathologies such as peripheral neuropathies, myopathies, or neuromuscular junction disorders can also be identified.
What an EMG cannot diagnose:
- Brain or spinal cord injury
- Muscle or tendon injury
- Bone or joint injury
Common EMG pitfalls
Electrodiagnostic testing is an operator dependent test. Be cautious with results from “automated” devices or studies performed by non-physicians, as these are not as reliable as tests performed by trained physicians. Only Physiatrists and Neurologists undergo specialized residency training in EMG and nerve conduction studies. Skin surface temperatures can also influence test results and so it is imperative to perform nerve conduction studies only when the affected limb is appropriately warmed.
Another important factor to consider is when to order an EMG. It can take between 2 to 6 weeks to see electrodiagnostic changes after a nerve injury has occurred. Therefore, it is best to wait on ordering electrodiagnostic testing for a least the first 4 to 6 weeks after an acute injury. Conversely, if an acute injury is claimed, an EMG could be helpful immediately to determine if the injury is actually pre-existing.
Navigating the EMG report
EMG reports can be difficult to follow. A good EMG report, however should include the following:
- The reason for requested study
- A brief history and physical examination
- Raw data in table form
- Narrative summary of nerve conduction studies and EMG
- Clear statement if test is normal or abnormal
- Conclusion to include diagnosis, severity, localization, and prognosis if applicable
In conclusion, EMG and nerve conduction studies can provide an accurate assessment of muscle and nerve function. These tests are commonly used to diagnose conditions such as carpal tunnel syndrome or other peripheral nerve compression, pinched nerve in neck or back, peripheral neuropathy, or muscle disease. When a precise diagnosis is needed to evaluate numbness, tingling, or weakness, electrodiagnostic testing performed by a board certified Physiatrist or Neurologist should be considered.