Electrodiagnostic Testing
Dr Ivo Waerlop is one of a handful of chiropractic physicians in the state of Colorado who are approved by board of chiropractic registration and can perform electrodiagnostic tests. Dr Ivo performs nerve conduction studies (NCV) and Needle Electromyography (EMG).
What are electrodiagnostic tests?
Electrodiagnostics are a series of “electrical” neurological tests that examine various aspects of neurological function. They are both objective and quantitative and exist as the gold standard for assessing neurological function. They look at either the afferent (information going in to the nervous system) or efferent (information coming out of the nervous system) aspects of different neurological pathways.
Nerve Conduction Studies
Nerve conduction velocity studies (NCV) look at the efferent and afferent function of peripheral nerves. They measure the conduction velocity of an electrical impulse along the axon (or trunk) of a peripheral nerve. It tells us to what degree a nerve is physically “pinched” or damaged. The nerve is tested at various points to determine if there is a “block” along the direction of travel. It can be for problems in the arms or legs.
In order to understand nerve conduction studies we need to understand how nerves respond to injury. Nerves are compound structures consisting of many individual wires in an insulating covering called “myelin”.
When there is compression on a nerve, a “conduction block” will occur. This often temporarily blocks the nerve impulse from traveling along the axon of the nerve. This happens when you cross your legs and your foot falls asleep. When the pressure is removed, the nerve usually returns to normal function. This “reversible conduction block” is short term and most often results in no permanent neurological deficit. It will usually yield a normal NCV test.
If pressure remains on the nerve for a long enough period of time, the nerve will lose some of its myelin sheath. This will cause the nerve to conduct impulses more slowly, causing an increased conduction time or decreased velocity. This will usually yield a slowed speed of conduction along a nerve or what’s called an “increased latency” in an NCV test. This may or may not result in permanent neurological deficit depending upon the degree and extent of injury.
If pressure remains on a nerve for long enough, the nerve will die. This will result in a decrease in amplitude of the overall “nerve signal” as well as a decrease in velocity along the nerve axon. This usually results in some degree of permanent neurological deficit and/or atrophy of the innervated muscle.
Electromyography
A test commonly performed along with an NCV is an EMG. An EMG uses a needle to measure the electrical activity in a muscle at rest and during a contraction. This confirms what is seen on the NCV and will often help determine the difference between a nerve root and peripheral nerve problem. It the nerve to a muscle is damaged, the muscle will start to atrophy or degenerate. As it atrophies, its outer sheath (the sarcolemma) becomes more sensitive, often causing the muscle to fire spontaneously. In the beginning, this occurs in just a few muscle fibers so it can’t been seen with the naked eye but is seen on the EMG. After sufficient degeneration, you can often visually see the muscle firing; this is called a fasiculation. Degeneration causes the muscle to become weaker and when it contracts, will have an incomplete or diminished ability to contract, also seen with the EMG. As the muscle gains its nerve supply back, it does so with larger motor units, increasing the muscles action potential amplitude which is also measurable. So, EMG helps us to see if a nerve and muscle are damaged, and whether it is improving or getting worse.
Nerves can heal. As long as the epineural sheath (the outer covering of the nerve) remains intact, the nerve may regenerate some of its myelin sheath, sprout new axons to innervate the muscle and return to normal function. Since nerves usually grow at a rate of approximately one inch per month, electrodiagnostic studies can tell you the following:
1. Where is the problem?
2. How bad is the condition?
3. Is the condition improving or worsening?
4. How far along is the healing process?
5. What is the prognosis?
If you have further questions about any of these tests, please call and speak with Dr Ivo or Dr John