S/D curve

Richard, thank you for your comment. I agree that the Faradic/Galvanic test is a second possibility (next to the S/D curve) to know whether the muscle is denervated or not. However, I must admit that I didn't think of the F/G test earlier and tried it this morning right after reading your comment. The test took me a little more time than calculating the AQ because the electrotherapy device I used has preprogrammed protocols for S/D curve and not for the F/G test. By the way, same with most electrotherapy devices on the European market that I know.

On the other hand, now that this discussion is somewhat re-opened, let me get back to my question. Taking into account that it only takes 3 minutes, wouldn't it be a good idea to start a S/D curve in every situation of muscle weakness with unknown cause? If the AQ (which is the part that only takes 3 minutes) shows > 2.7 one can stop at that point. Hardly takes time, no harm done and no need to go through a complete anamnesis. But if the AQ shows < 2.7 a complete S/D is necessary.

Patrick

Patrick I think that a Galvanic/Faradic test would save even more time. If the patient has a muscle response with a pulse duration of 1 ms it suggests no nerve injury. The patient's history also helps us to decide what path we should take.

Thank you Tim and Richard.

@ Tim: yes, your comment is of great help, I'll get back to it later on. @ Richard: I agree that without a suspicion of a nerve injury there is no need for a S/D curve. The question is, do we always know if there is a nerve injury? My idea is that we do not and what I'm trying to make here is a clinical reasoning flow chart for the S/D curve. So let's suppose the clinical examination shows a muscle weakness and the therapist hasn't got the slightest idea where that comes from. Taking into account that it doesn't even take more than three minutes to get the accommodation quotient (AQ), my idea is that in every case of muscle weakness of unknown origin, the S/D curve is useful. With an AQ > 2.7 one can say, ok let's use NMES type currents and support the exercise therapy. With an AQ < 2.7 it's all hands on deck because we've got a nerve injury here and that requires a different approach. Does everyone agree so far?

Patrick

I also only use a S/D curve when I suspect the pacient has a peripheral nerve injury. Changes in Rheobase, Accomodation and Cronaxy are very useful to determine the injury type and specially to help us to choose the electrical parameters to perform a selective muscle stimulation. If patient has a muscle weakness without a suspiction of nerve injury I don´t think S/D curves are necessary. You can just use a conventional NMES device to help the voluntary contraction or only perform a voluntary resistive trainning.

Last updated 3 years ago

Patrick. In the scenario that you describe, I would say that the published evidence would support the COMBINED exercise + NMES approach - not that it necessarily changes the outcome, but that it takes less time to get there - and thus from a patient perspective, there is added benefit from the use of NMES as a component of the treatment package. Exercise alone can get a result - we all know that - but adding the NMES has added value. Any help??

Hello Patrick 15 years ago I've taken S/D curves in +/- 100 horses. Since then I've simplified the technique. As most of TENS machines work with pulsewidths of 250usc, When diagnosing horses I increase the intensity and measure the intensity at which the first muscle twitch is visible. This gives me an idea about the severity of the neuro or'muscular lesion. Helps me to make a prognosis and helps me in evaluation the progress of treatment. In some case I had the opportunity to compare my conclusions with EMG and they seemed to be similar. Fo me it is very usefull in my equine practice. In the canine the method is not interesting because muscles are to small and the neighbourgh muscle starts twitching to easy Hope this can help

Thank you for your comments. So far I see the same problems as some of you do, hardly anyone knows what the S/D is hence what the benefits are. So, if it's ok for you all, I'd like to get on with this discussion but let's take it step by step.

I'll come back with my ideas on "why in every case of muscle weakness?". But first I would like to get something else sorted out. Let's suppose a S/D shows all signs of normal innervation in a patient with a clear atrophy. Let's say the patient had a ski accident, broke his femur, had his leg 6 weeks in a cast, after 6 weeks Xrays showed good calcification and the patient can start his rehab. Due to the 6 weeks inactivity his quadriceps shows a clear atrophy. Does in such a case everyone agree that NMES type of muscle stimulation + exercise therapy gives quicker results than exercise therapy alone?

Patrick

Great discussion. I agree with the clinical use of undertaking an SD test to provide an 'important piece of the puzzle' ( ie. one piece of information) to inform clinical decisions as to whether there is value in proceeding with NMES of 300-400 microsec). It is relatively quick, inexpensive and non-invasive. I have used it with several clients who had peripheral nerve injuries and, without exception, the patients and physicians have been appreciative of the information to inform subsequent decisions for management.

Patrick. Agree with other contributors that SD curve has a distinct clinical value - and as Cliff says, if nothing else, it will help to determine whether NMES type stimulation with pulse durations of up to 300 or 400 microsec would be in any way valuable. When I suggest such a test to currently practicing therapists, the majority are neither familiar with the test nor the interpretation of the results - I think that as a professions we are missing the opportunity to deliver quick, low cost but insightful clinical test option - but that may be because I did my physio training 'some while ago' and can see its clinical merit

I like this question because I have performed so many S/D tests over the years. Most often responding to a patient request or Insurance company request in the presence of known peripheral nerve injury to provide a portable muscle stimulator for the patient to use at home. A quick full S/D test will show whether a 300 microsec current has even the remotest chance of producing a contraction. Follow-up tests are indicated. Other occasions include adult hand injuries (one time a radial nerve injury in a child) repaired in the ER with missed nerve involvement that was picked up a few days later with an S/D test in PT dept. And many other interesting cases where status of the nerve was important. My experience has been that mostly clinics did not have the appropriate equipment and the PTs did not have the skills to perform the test so they came to me at an academic centre! I believe that PTs consider S/D tests unimportant because there are far more refined neurological tests. On the other hand, S/D tests can be done without wait time and are invaluable in suburban & rural practice.

Hi Patrick I totally agree with Oscar to use the s/d curves to establish the patency of a nerve. Then you can decide whether to use ac NMES to activate the motor nerve or DC to stimulate the muscle cell directly When a muscle tests weak it may not be due to neural damage but Autogenic Muscle Inhibition (AMI) may occur due to muscle trauma, systemic illness or an adverse reactio to the medication used in ventilation Either way intervening with Muscle Stim is a good modality option BW Cliff

Dear Patrick

I allways use a S/D curve when the patient have a peripheral lesion. With this test it's possible to see the cronaxy and then, determine the type of lesion (total, severe, moderate, slight and finaly, no lesion).

What do you refer to with "weak muscle"?

Best, Oscar