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Relative sparing of EDB on NCS
Hi all,
I'm interested in your opinion regarding relative sparing of the EDB muscle compared to an atrophic tibialis anterior. I have seen this occasionally in myopathy and dystrophy patients.
I recently had a very complicated study for left foot drop and bilateral lower extremity numbness/burning in a 77 year old in which the left tibialis anterior muscle was visibly atrophic and bilaterally the TAs had low amplitude CMAPs [1.0;symmetric], yet the EDB were bulky with high normal CMAP amplitudes (left [foot drop side] was 3.6; the other was 8.7). There were not sensory or tibial abnormalities. A very comprehensive EMG Bilateral lower and some uppers) showed no myopathic findings at all. There were very significant, mostly chronic or sub-chronic reinnervation changes in all distal > proximal leg muscles bilaterally and in the left FDI with denervation (PSWs and fibs) in the left tibialis anterior only (the foot drop side).
The lumbar MRI doesn't show anything that would cause multilevel radiculopathy -- it's pretty normal. I feel that the time course (onset of foot drop 7 years ago) and relative paucity of active denervation would be atypical for ALS plus the robustly normal EDB muscles in the setting of ALS with foot drop would also be atypical.
Is this EDB sparing significant? What does it make you think of?
Thanks for your thoughts--
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