pikachu said:
I had originally posted in neurology but realized it was a low traffic thread so I tried to delete it. I hope to get an answer here...
Can anyone shed some light on the specific clinical indications for nerve conduction studies? I'm working with an internist right now who orders them on any patient complaining of any kind of nerve pain whatsoever - diabetic neuropathy, sciatica, impingement, whatever. Most of the patients do not have clinically detectable weakness or sensory loss (some of the diabetics have mild sensory loss). Not that she would know, she generally doesn't even do a neuro exam. I would guess about 1/4 of her patients have had nerve conduction studies done. I'm only a fourth year but I've never seen anyone else (in internal medicine or neurology) practice this way and I'm just wondering what the standard guidelines are for ordering this test. Thanks.
Yeah, well, you should have left it on the neurology board instead of driving me crazy trying to figure out where it disappeared to before I could answer it . . . By the way, the next most logical place to go would have been the PM&R site, since they do the studies as well.
Oh, boy, can I go to town on this one. I get lots of EMG consults from primary care providers for patients with vague complaints and stone cold normal exams. I usually (but not always) do the test, but I just have to shake my head and wonder to myself "what were they thinking?"
The purpose of nerve conduction studies (NCS) (and it's complementary test, EMG) is to identify, localize, differentiate, and prognosticate with regard to lesions of the peripheral nervous system and muscle. There are really no "specific" indications, but common sense and some idea of neuroanatomy should come into play. NCS and EMG should be thought of as extensions of the neurologic exam -- if you have a patient who fits a pattern of peripheral neurologic disease, it can help you sort things out. Problem is, in the hands of the clueless, it's just about worthless, and may even confuse things more. As you yourself pointed out, it's much more meaningful if your patient actually has some type of objective sensory or motor deficit to correlate to the NCS/EMG. As with any test (radiology, lab, etc) there should be some meaningful clinical correlation between exam findings and symptoms. For example, lets say someone is referred for NCS/EMG for "shoulder pain": normal neuro exam, and the NCS shows only mild sensory slowing across the median nerve at the wrist. Relevant? Probably not. Do they have "carpal tunnel syndrome?" Nope. They may have an asymptomatic mild median neuropathy that nobody is going to do anything about and doesn't explain their shoulder symptoms. On the other hand, how about someone with diabetes and constant burning pain in the feet and some stocking-distribution loss of pinprick sensation, suspected of having peripheral neuropathy? You do their NCS/EMG and it's completely normal. Do they have peripheral neuropathy? Probably. It's just that routine nerve conductions don't adequately assess the small-fiber unmyelinated nerves that mediate pain sensation. Remember: a normal test never rules anything out completely.
The internist you are working with is not doing her patients any favors by sending them willy nilly for nerve conduction tests. In fact, the test itself is kinda painful and her patients with normal tests won't be thanking her for the experience. On the other hand, the neurologists will be happy to do them, since they bring in better $$$ than just another headache referral. The better plan would probably be to refer them to a neurologist for a consult and let the neurologist make the call as to whether the exam will be useful.
