Negative EMG/NCV so I don’t have neuropathy? Not so fast!!
(You can skip to the chase here – you CAN have peripheral neuropathy with a normal EMG/NCV)
A very common method of testing for peripheral nerve damage are electromyelegrams (EMG) and nerve conduction velocity (NCV) tests, they are called electrodiagnostic tests as well. A good way to think about how they work is that they shoot electrical impulses into one end of your nerves and measure how fast and how “big” the impulses come out of the other end.
Based on this testing, the clinician might be able to get a sense of whether the damage is to the ENDS of the nerves (like the hands/feet) or if the problem is at the BEGINNING of the nerves (like a herniated disc by the spine).
You are entitled, however, to have multiple things wrong with you
Keep in mind that there is no limit on what you can have wrong with you. Can anyone think of a reason why you couldn’t have a nerve issue up top (like sciatica or a “pinched” nerve) as well as some damage at the ends of the nerves? Nope! You are entitled to have many things wrong with you at once.
Off of the top of my head I would guess that about 20% of the patients that I see in my practice have issues at the ends of their nerves (from peripheral neuropathy) as well as some problems at the beginning of their nerves (like disc degeneration or lumbar stenosis or something).
But many times it is one or the other or the symptoms are from mostly one or the other. These tests can help determine if it’s one or the other or both.
But what if you have a “negative” EMG/NCV?
Does that mean that you don’t have neuropathy? Not necessarily. You see, these two tests are only good for nerves that have a myelin sheath. Think of myelin as the insulation around an electrical wire. Its purpose is to speed up nerve impulses for things that have to go FAST like all of the quick corrections we do to stand and walk upright, feel touch, vibration, etc. In general, these types of nerves are called large diameter nerve fibers. Large fiber damage will mostly give symptoms of numbness, tingling, weakness, and loss of coordination (the body loses track of its feet/parts).
If there are large diameter nerve fibers, there must be small diameter nerve fibers right?
And problems with these nerves are not picked up by the EMG/NCV tests.
John Hopkins School of Medicine website lists the symptoms of small fiber neuropathy as:
That covers a lot of symptoms right?
Confusingly enough there is overlap between the symptoms caused by small fiber damage and large fiber damage. This overlap is not normally a major issue, as many times there is both large and small fiber damage. Here; however, we are addressing someone that might have only small fiber damage.
Since the EMG/NCV only picks up large fiber dysfunction, one can certainly have a negative EMG/NCV and still have peripheral neuropathy.
Just small fiber peripheral neuropathy – not large fiber peripheral neuropathy.
If someone has the signs and symptoms of peripheral neuropathy and they get a normal EMG/NCV, there is testing that can be done for small fiber neuropathy. It’s a tissue biopsy where a small plug of tissue is taken and sent off to a lab. In the lab the tissue is stained and the small fibers are literally counted under a microscope. (Sounds like a thrilling job)
With small fiber neuropathy there will be FEWER nerve fibers than normal. Counterintuitive right? Well neuropathy is weird.
At my clinic, we treat both large and small fiber neuropathies. The small fiber folks see a reduction in intensity and surface area symptoms. The same goes for those with large fibers in regards to numbness, but they have additional work to do on some of the strength and coordination issues. Many patients have both small and large fiber damage and have pain AND numbness.
How on earth can you have pain AND numbness? If you are going numb then why does it hurt?
I write about that here