radic vs sciatic nerve?

[topwise]

Any thoughts on this one:

Woman s/p left hip replacement, which dislocated. Now with footdrop on the side of the THA. She also has an MRI showing a herniated disc at L4-5.

NCS: Peroneal response unobtainable at EDB, very small at TA on left. Borderline normal peroneal on right. Tibial CMAP amp somewhat smaller on left. H's normal bilaterally. Sural's normal bilaterally. Superficial peroneal unobtainable bilaterally.

EMG: TA and FDL strongly positive. Gastroc negative, biceps femoris (short head) negative, quads neg. TFL and gluteus medius 1+ PSW. Paraspinals negative.

We were kind of stumped. I was going to go with an L5 radic, even though the paraspinals were negative.

---

Members don't see this ad.

 

[Ludicolo]

What does “tibial CMAP amplitude ‘somewhat’ smaller” mean? Either it’s low amplitude or not. Wouldn’t call it abnormal unless it’s below normal values, or there is a 50% side-to-side difference.

If your TFL and Gmedius are abnormal, lesion has to be proximal to the sciatic nerve, either radic or plexus. But you might also have mild abnormalities in these muscles - residua from her prior surgery. You can see normal paraspinal EMG findings in old radics, but with the absent super-p’s I don’t think you can say definitively this is a radic. Clinically, assuming her foot drop came on after her hip dislocation, this sounds sciatic. Invoke “fascicular involvement” with the short head of the biceps femoris.

You’re trying to get me to say “double crush”, aren’t you?

 

[topwise]

Tibial CMAP amp was like 5.5 on the good side, 3.5 on the bad side. So kind of borderline.

I thought maybe the superficial p's were unobtainable because of her age (80 years). I figured since they were absent bilaterally, it wasn't helpful.

Yes, we were kind of thinking double crush I thought maybe she had an old L5 radic causing the proximal findings and then a sciatic neuropathy on top of that causing her footdrop. What confused me also though was that the TA and FDL were SO strongly affected and the gastroc was completely spared. I know that sciatic neuropathies tend to preferentially affect peroneal fibers so that explains the lack of findings in the gastroc, but the FDL is tibial, so what gives?

And one thing I forgot to mention was that in the short head of the biceps, even though there were no psw's or fibs, there was one CRD we kept finding.

 

[SSdoc33]

TA is more 4 than 5, and the MRI can be helpful here, IMHO. plus, FDL isnt exactly the easiest muscle to be sure that you are in. if the herniation looks bad and it is directly on the L5 nerve, than a radic copuld be more likely. in an 80 y/o, there may be a decent amount of baseline stenosis, so the CRD is likely non-specific and has probably been there for years

 

[olafa]

Did you do an H-reflex?

 

[topwise]

In answer to questions:

MRI showed significant stenosis at L4-5 that seemed to be impinging on L5 root.

I originally said H's were normal, but on checking again, they were slightly prolonged on the affected side. I'm not sure how that helps though, since it would be for an S1 radic.

 

[njdevil]

I think your history and clinical exam must be utilized to tease this out. MMT, sensory, reflexes. Also, how long has it been since the surgery to the emg/ncs?

 

[topwise]

The symptoms started a few days after the hip replacement. But the surgery was especially traumatic and it was felt that there might have been stress on the already damaged spinal nerves.

 

[Ludicolo]

njdevil raises an important point: when was the EMG performed with respect to the hip surgery/injury? What did the MUAPs look like in the affected muscles?

 

[PMR 4 MSK]

I've struggled with similar cases over the past few years. EMG greatly loses it's utility for proximal lesions, especially in the leg. The lumbosacral plexus is quite complex, and there is more variability in the leg with regards to innervation than there is the hand.

I once had a case of an "All Tibial Foot" - no sigificant peroneal innervation. Tibial innervated EDB. I believe it was unilateral.

 

[spondy14]

I have also had difficulty confirming these cases with EMG. I also rely heavily on the clinical story. Also, I am guessing that the pt. is not currently complaining of any pain, which in this case would mean that you stick on an AFO and wait for it to come back. I don't see a spine surgeon going in if it is likely a sciatic problem (which from clinical history is more likely). You would expect more pain with a radic, although having said that I have seen older patients with weakness and very little pain. I have a hard time even using paraspinals for diagnosis, and even if you did see PSW's in the PS, would it confirm a radic for you? Not hardly for me. If someone has a dislocated hip with foot drop, I would have a hard time calling a radic the cause. Tough case.

 

[topwise]

We ended up calling it a sciatic neuropathy, with the spont activity in the gluteus medius and TFL a result of surgical manipulation. (FYI, the EMG was done 3 weeks after the surgery)

 

[PMR 4 MSK]

You also have to be very, very careful with over-calling these exams, as there is a significant chance of the ortho getting sued. And since this is not cut-and-dry, he will hire another EMG'r to rip your report apart.

You gotta be neutral, but don't over-call. You could make bad enemies.