Deep Motor Branch Ulnar Neuropathy

[DistantMets]

We had an interesting case last week of a lady with a deep motor branch ulnar neuropathy from a pretty severe 5th metacarpal fx. Ulnar CMAP to the ADM was normal (didn't compare her other side though) and to the FDI the amplitude was less than 1 (0.4? I'd have to look again). Ulnar SNAP was normal. My attending was able to get a low amplitude DUC despite the surgical scar. She couldn't adduct her 2nd and third fingers and had 3/5 finger ADM/FDI. Needle of her FDI>ADM showed denervation while her ulnar FDP and FCU were normal.

Just thought I'd share, I don't see many ulnar CMAPs to the FDI and it was really what made the dx. I will probably do it more also to catch the differential slowing across the elbow when I'm really suspicious and the ADM is normal.

---

Members don't see this ad.

 

[topwise]

Interesting. I wonder how many EMGers commonly record off the FDI when doing an ulnar study.

 

[PMR 4 MSK]

Interesting. I wonder how many EMGers commonly record off the FDI when doing an ulnar study.

Uncommon as primary muscle, but some do it. I'll use it as confirmatory in quesitonable cases.

 

[latinman]

Why did you guyz do a DUC study? Did she have sensory problems in the dorsum of the hand? I hate to play the devils advocate, but the DUC came back low in that arm which raises the concern about whether this compression or nerve damage is taking place proximal to the wrist. I understand how the dorsal hand area might have been scarred. The fact that her FCU and FDP muscles were spared would speak against UN at the elbow. However, did you guyz run the FDI across the elbow?

At times ulnar neuropathies at the elbow will have preference when it comes to the nerve fibers that are damaged/involved (At least theoretically). In other words, the ulnar fibers across the elbow that go to the FDI might be affected while the ulnar fibers that go to the ADM are spared.

Also, what was the latency difference between the FDI and ADM (If less than 2; that would speak against UN at wrist). Other things to have considered would have been inching across the ulnar wrist while recording at the FDI (looking for focal slowing delay greater than 0.5 ms for every inch) or wrist/midpalm stimulation looking for conduction block or conduction velocity slowing > 37.

 

[DistantMets]

Why did you guyz do a DUC study? Did she have sensory problems in the dorsum of the hand? I hate to play the devils advocate, but the DUC came back low in that arm which raises the concern about whether this compression or nerve damage is taking place proximal to the wrist. I understand how the dorsal hand area might have been scarred. The fact that her FCU and FDP muscles were spared would speak against UN at the elbow. However, did you guyz run the FDI across the elbow?

At times ulnar neuropathies at the elbow will have preference when it comes to the nerve fibers that are damaged/involved (At least theoretically). In other words, the ulnar fibers across the elbow that go to the FDI might be affected while the ulnar fibers that go to the ADM are spared.

Also, what was the latency difference between the FDI and ADM (If less than 2; that would speak against UN at wrist). Other things to have considered would have been inching across the ulnar wrist while recording at the FDI (looking for focal slowing delay greater than 0.5 ms for every inch) or wrist/midpalm stimulation looking for conduction block or conduction velocity slowing > 37.

We did do a full ulnar motor to the FDI around the elbow and no slowing. My attending is very thorough and does a lot of FDI studies (she has a hand surgeon that is probably putting her kids through college). She did have some numbness in the DUC distribution but not on the hypothenar eminance or palmar 4th/5th digits. We suspected it was post-surgical. We did the DUC just to see if we could get it and I was surprised when we did. The fact that it's not normal does muddy the waters a little admittedly. She had a scar the entire length of the 5th met and I think her surgery was 2 months ago. We looked up some articles and found that the usually ADM gets one the 1st branches to the hypothenars, so we suspect the fracture did most of the damage in the hand, rather than at the wrist. There was no associated wrist injury. She denied any N/T or weakness in the hand before the accident. Plus, I would be surprised to see a 90% distal amplitude drop going to the FDI with a completely normal ADM if you had a severe lesion across the elbow...maybe one's normal and you'd have slowing or mild conduction block in the other.

Anyway, thanks for the feedback...I like these kind of cases!

 

[DistantMets]

Why did you guyz do a DUC study? Did she have sensory problems in the dorsum of the hand? I hate to play the devils advocate, but the DUC came back low in that arm which raises the concern about whether this compression or nerve damage is taking place proximal to the wrist. I understand how the dorsal hand area might have been scarred. The fact that her FCU and FDP muscles were spared would speak against UN at the elbow. However, did you guyz run the FDI across the elbow?

At times ulnar neuropathies at the elbow will have preference when it comes to the nerve fibers that are damaged/involved (At least theoretically). In other words, the ulnar fibers across the elbow that go to the FDI might be affected while the ulnar fibers that go to the ADM are spared.

Also, what was the latency difference between the FDI and ADM (If less than 2; that would speak against UN at wrist). Other things to have considered would have been inching across the ulnar wrist while recording at the FDI (looking for focal slowing delay greater than 0.5 ms for every inch) or wrist/midpalm stimulation looking for conduction block or conduction velocity slowing > 37.

Oh, and she did do the palm stim. No conduction block and I don't recall a latency difference. We didn't do any inching.