Abstract Details

Title Concentric Needle Voluntary Jitter Assessment in Patients with Mitochondrial Myopathy.

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P3 - Poster Session 3 (5:30 PM-6:30 PM)

Poster/Presentation
Number 1-008

Objective To describe jitter abnormalities in voluntary single fiber electromyography using disposable concentric needle electrode (CNE) in patients with mitochondrial myopathy (MM).

Background

Patients with MM may show the same abnormalities in single fiber electromyography (SFEMG) as patients with myasthenic syndromes. More recently, disposable CNE is replacing single fiber electrode for jitter assessment, but there are no reports of its use in MM.

Design/Methods We selected 19 subjects (mean age 48.2 ± 16.5 years) with chronic progressive external ophthalmoplegia diagnosed with MM confirmed by muscle biopsy. In all patients, we collected 20 apparent single fiber action potential (ASFAP) pairs during minimal voluntary activation of orbicularis oculi muscle using disposable CNE. Jitter values were expressed as the mean consecutive difference (MCD) and those values exceeding 150µs were fixed to 150µs to avoid the effect of the velocity recovery function. CNE jitter assessments with 3 or more ASFAP pairs with individual MCD above 45µs (criterion A) and/or mean jitter above 31µs (criterion B) were considered abnormal.

Results Five of 19 patients (26.3%) presented an abnormal jitter analysis. Of these, four patients met criteria A and B. The other patient had only two abnormal ASFAP pairs, but had a mean jitter of 39µs and met criterion B. All of these five patients had at least one ASFAP pair with evidence of impulse blocking. Three of 19 patients (15.8%) had only one abnormal ASFAP pair, with no impulse blocking and did not meet criteria A or B. The remaining 11 patients (57.9%) had a completely normal test. The average jitter of all patients was 27.9 ± 9.4µs (range 18.5–46.9).

Conclusions

Similarly to studies with SFEMG, CNE voluntary jitter assessment can present various abnormalities in patients with MM, including impulse blocking. These findings may lead to a misdiagnosis of a myasthenic syndrome if not interpreted in the right clinical context.

Authors/Disclosures
Vitor M. Caldas, MD (Hopital Das Clinicas Da Universidadede Sao Paulo) PRESENTER	No disclosure on file
Eduardo Estephan	No disclosure on file
Andre M. Silva, MD (Departamento De Neurologia Do Hospital Das Clinicas FMUSP)	No disclosure on file
Rodrigo de Holanda Mendonça	No disclosure on file
	No disclosure on file
	No disclosure on file
Edmar Zanotelli	No disclosure on file

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