AANEM Connect

Hello all, 

I would like to collect the thoughts and opinions on the interpretation of jitter study/single-fiber EMG. 

Short version: In an otherwise normal jitter/SFEMG study performed with disposable concentric needle electrode, does having 1 pair (out of 20) with increased jitter WITH blocking make the study abnormal?  If so, I am looking for some literature supporting this statement. May be I am missing it while it is in plain sight. I need some help finding this info. 

Long-version: 
Clinical history: 48-year-old African-American woman presenting with 15-year history of generalized weakness, 2 years of fatigable ptosis, 1 year of dysarthria, intermittent binocular diplopia, shortness of breath.  Reports having exposure to Pyrethrin (organophosphate) since the age of 11.  Neurological examination at the time of jitter/SFEMG study was only notable for some dysarthria but ocular and general motor examination was within normal limits.

Current medication regimen: IVIG q. monthly and mestinon with subjective improvement. 

Prior work up: Underwent serological testing for myasthenia gravis X3 times.  One of the times was noted to be positive for  AchR modulating antibodies but on repetietion negative.  Prior EMGs with repetitive nerve stimulation was negative. Also had a muscle biopsy reported to be normal. 

She was evaluated by at least 4 different neurologists and our group is the fifth.

Jitter studies: Patient does not have any history of botulinum toxin.  No more exposure to pyrethrin.  She had been off pyridostigmine for more than 24 hours prior to her study.

Study was performed on the right frontalis muscle with voluntary activation using disposable concentric needle electrode.  Data as documented in the tabular format,  and videos.

Apart from the single pair that shows increased jitter with blocking, rest of the study is normal.  From what I remember, having a block even in a single pair makes the study abnormal.  But, I am not able to find any data supporting the statement.  Here are my questions: 

1.  Is it commonly accepted that having a block (ofcourse with increased jitter) on a single pair makes the study abnormal ? Like I said before, I may be missing it in plain sight. If so, I would like to get some literature evidence to support the statement.  I remember hearing this, but I also remember hearing other views. 

2.  If it is felt that this particular pair has a quality issue and should be excluded out of the analysis, in that case would like to understand why and what could have been done better.

Please note: This question is strictly related to interpretation of single-fiber EMG/jitter studies and would appreciate limiting the discussion towards electrodiagnostic interpretation rather than clinical.

Thank you in adavnce for your time and expertise.

Best,
Sri Raghav Sista, MBBS
Asst. Prof of Neurology - UTHouston