This week's interesting case

[PMR 4 MSK]

59 y/o female, Workman's Comp case. Bilateral CTS Dx'd last year, underwent open right Carpal Tunnel Release 1/08. Since the surgery, symptoms are worse - numbness, pain in median nerve distribution and new weakness of the thumb. Pt sought 2nd opinion from one of our ortho's. He notices the pt can abduct the thumb, but cannot oppose. He refers for repeat EMG, to look for dystonia - the thinking here that if the APB is working, OP should be too.

Last EMG was about 15 months ago. Ulnar motor and sensories normal then and now. Median motor amplitude has dropped from 2.5 mV to 1.3 since the previous EMG. Median motor distal latency unchanged at 4.8 ms, forearm NCV unchanged around 45m/s. Median sensory improved in distal latency (orthodromic) from previous of 4.5 to 3.2, amplitude increased from 7.0 to 12 from the previous EMG.

Previous needle exam listed increased IA, 1+ fibs and PSW's with decreased recruitment of the APB. Today, APB shows still increased IA, 2+ fibs and PSWs and only 2-3 viable motor units at a time - significantly reduced recruitment.

So I needle the opponens pollicis and it shows increased IA, 2-3+ PSW's and fibs and no MUAP's or recrutiment - completely denervated. Superficial head of FPB shows 1+ Fibs and PSW's and near-normal MUAPs and recuitment, with slightly increased polyphasia. Ulnar and proximal muscles, including pronator teres all normal on needle exam.

Morales of this story - 1) you can get unequal distribution of denervation in the muscles of the thenar eminence in CTS, which in this case, correlates with the inability to oppose, but preserved abduction - probably using FPB to assist APB. 2) Even with open CTR, you may not get release of the carpal tunnel and the nerve can continue to get worse.

Did the surgeon actually harm the nerve while attempting to help it, or did his surgery just fail to work? Would you advise the patient to undergo repeat CTR and/or exploration?

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[SSdoc33]

59 y/o female, Workman's Comp case. Bilateral CTS Dx'd last year, underwent open right Carpal Tunnel Release 1/08. Since the surgery, symptoms are worse - numbness, pain in median nerve distribution and new weakness of the thumb. Pt sought 2nd opinion from one of our ortho's. He notices the pt can abduct the thumb, but cannot oppose. He refers for repeat EMG, to look for dystonia - the thinking here that if the APB is working, OP should be too.

Last EMG was about 15 months ago. Ulnar motor and sensories normal then and now. Median motor amplitude has dropped from 2.5 mV to 1.3 since the previous EMG. Median motor distal latency unchanged at 4.8 ms, forearm NCV unchanged around 45m/s. Median sensory improved in distal latency (orthodromic) from previous of 4.5 to 3.2, amplitude increased from 7.0 to 12 from the previous EMG.

Previous needle exam listed increased IA, 1+ fibs and PSW's with decreased recruitment of the APB. Today, APB shows still increased IA, 2+ fibs and PSWs and only 2-3 viable motor units at a time - significantly reduced recruitment.

So I needle the opponens pollicis and it shows increased IA, 2-3+ PSW's and fibs and no MUAP's or recrutiment - completely denervated. Superficial head of FPB shows 1+ Fibs and PSW's and near-normal MUAPs and recuitment, with slightly increased polyphasia. Ulnar and proximal muscles, including pronator teres all normal on needle exam.

Morales of this story - 1) you can get unequal distribution of denervation in the muscles of the thenar eminence in CTS, which in this case, correlates with the inability to oppose, but preserved abduction - probably using FPB to assist APB. 2) Even with open CTR, you may not get release of the carpal tunnel and the nerve can continue to get worse.

Did the surgeon actually harm the nerve while attempting to help it, or did his surgery just fail to work? Would you advise the patient to undergo repeat CTR and/or exploration?

good case and good questions. i would probably have it re-explored. you have evidence of clinical worsening and possible electrodiagnostic evidence of worsening. you dont have much to lose with a re-exploration. the surgeon may have to somehow enlargen the canal, if thats possible. my guess is that there was no injury to the median nerve during the surgery, but that it was not completely decompressed or there is excessive scarring within the canal. does the patient have dark skin? keloid?

sometimes if find the SNAPs are normal in CTS, but motors are prolonged. i always think thats just weird. i guess you can get anything, though.

 

[PMR 4 MSK]

good case and good questions. i would probably have it re-explored. you have evidence of clinical worsening and possible electrodiagnostic evidence of worsening. you dont have much to lose with a re-exploration. the surgeon may have to somehow enlargen the canal, if thats possible. my guess is that there was no injury to the median nerve during the surgery, but that it was not completely decompressed or there is excessive scarring within the canal. does the patient have dark skin? keloid?

sometimes if find the SNAPs are normal in CTS, but motors are prolonged. i always think thats just weird. i guess you can get anything, though.

Pt eastern-European, mild keloid externally.

 

[Ludicolo]

There are case reports of the motor branch of the median nerve piercing the flexor retinaculum, or even lying superficial to the retinaculum. There are also case reports of anomalous innervation (like an accessory motor branch), which may have not been adequately decompressed.

 

[PMR 4 MSK]

There are case reports of the motor branch of the median nerve piercing the flexor retinaculum, or even lying superficial to the retinaculum. There are also case reports of anomalous innervation (like an accessory motor branch), which may have not been adequately decompressed.

Any reliable way of testing for these pre- or post-op?

 

[Ludicolo]

Any reliable way of testing for these pre- or post-op?

Not sure. Most of the case studies are surgical reports (with little to no mention of EDX studies), or cadaveric studies.

However as SSdoc33 alluded to, if the median motor abnormalities are relatively more severe than the sensory abnormalities this may suggest this possibility. An abnormal median motor amplitude recorded over the lumbricals (axons are normally relatively spared in CTS due to fascicular involvement) - especially in the setting of normal/mild median sensory responses – would be further evidence to suggest that something ain’t right.

Perhaps with more sophisticated improvements in musculoskeletal ultrasound, or maybe MRI, one might be able to better detect this type of anatomy.

The way I approach it – if my EDX findings don’t make sense with the clinical picture either 1) there’s a technical error, 2) the differential diagnosis may need to be re-evaluated, 3) I'm detecting something else subclinically, or 4) consider an anomalous innervation/weird anatomy.