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Single fiber electromyography in normal subjects: reproducibility, variability, and technical considerations
1EMG Laboratory, Columbia Presbyterian Medical Center, New York, New York 10032.
Electromyography and Clinical Neurophysiology
|July 1, 1992
Summary
Single fiber electromyography (SFEMG) is reliable for spasmodic torticollis, but interpretation requires care, especially in older patients. Abnormal jitter is rare in normal muscle, often appearing in multiples.
Area of Science:
- Neurology
- Neurophysiology
Background:
- Spasmodic torticollis is a focal dystonia affecting neck muscles.
- Single fiber electromyography (SFEMG) assesses neuromuscular transmission.
- Guidelines for SFEMG interpretation exist but require careful application.
Purpose of the Study:
- To evaluate the diagnostic utility and reliability of SFEMG in patients with spasmodic torticollis.
- To identify the prevalence and characteristics of abnormal jitter in this patient population.
- To assess the impact of age and technical factors on SFEMG findings.
Main Methods:
- 59 SFEMG examinations were performed on 33 patients diagnosed with spasmodic torticollis.
- Serial examinations were conducted on 14 patients over a 12-week period.
- Data analysis focused on jitter values, fiber pairs, and potential technical issues.
Main Results:
- Excessive jitter (>55 microseconds) was found in 1.1% of fiber pairs.
- Abnormal jitter was infrequent, occurring at more than 2 sites in only two elderly patients.
- Technical issues and specific patterns (triplets, pairs) were noted in abnormal findings, particularly in older individuals.
Conclusions:
- SFEMG is a valid and reliable technique for evaluating spasmodic torticollis when interpreted strictly by established guidelines.
- Special consideration is necessary for SFEMG studies in elderly patients due to potential age-related findings.
- Abnormal jitter in normal muscle is rare and typically presents as part of multiplets.