AANEM Connect

Hey all, 

Was hoping to pick the brains of folks who give lots of botox and/or have more experience than me (and what I can find in the literature) in how to interpret rep stim changes in patients who are receiving botox. 

I have a patient in her 30s who had a prior C spine surgery for a left C5/C6 radiculopathy and regained 90% of her strength after this surgery. For chronic neck/shoulder pain and migraines she has been receiving botox for migraine and also to the neck and trapezius muscles (around 350-400 units every 3 months). About a year ago she started to develop recurrent left sided weakness and repeat imaging hasn't shown new nerve root compression. I saw her a few months ago and thought she had bilateral proximal arm weakness. Prior EMG in 2023 reported "neurogenic changes" in several muscles in the left arm in keeping with a presumed radiculopathy. I re-studied her and found myopathic units in proximal muscles in both arms and given the relative symmetry decided to also do rep-stim in the hand (assuming that the trapezius and facial muscles would be clearly impacted by botox). This was positive with decrement of 14% at at baseline with repair of decrement and no facilitation with 10-sec and 60-sec exercise with return of decrement at 2-4minutes post-60-sec exercise.

My question is: is this consistent with systemic effect of botox or is it possible that the botox has unmasked another disorder like MG (antibodies negative) or a hereditary condition like a congenital myopathy, myasthenic syndrome or otherwise? The appearance of a more-typical post-synaptic finding on rep stim in a muscle very far away from any botox injection is what has me questioning whether botox can be blamed. 

Would appreciate any thoughts!

-Tom Ragole