SFEMG, or single-fiber electromyography, was established in the 1960s and has become an indispensably valuable method for diagnosing a variety of muscular disorders, particularly myasthenia gravis, especially when other tests prove inconclusive.
SFEMG requires a needle electrode with a very small recording surface necessary for measuring muscle fiber fatigue. Typically, single-fiber electrodes are prohibitively expensive and can cost $350 for each reusable needle.
However, fairly recent studies have suggested that concentric EMG needles, which are significantly more affordable, may offer a serviceable alternative to the single-fiber electrodes that are conventionally used in SFEMG.
SFEMG, Jitter, and Concentric EMG Needles
The core of single-fiber electromyography it to provide measurement of the interval between two action potentials of a single motor unit. The variation in the intervals is called “jitter” and increased levels of jitter are interpreted as indicators of myasthenia gravis, for the detection of which the SFEMG test is often administered.
Often, a single-fiber EMG needle is used to record jitter, and placed between two individual muscle fibers of the same motor unit. It can also detect fiber density, a measure of reinnervation.
However, recently, studies have suggested that concentric EMG needles may be used in place of single-fiber EMG needles for the purposes of recording jitter.
One 2006 study, in particular, showed that CNE, or concentric needle electrodes, may serve as a justifiable alternative to SFEMB needles.
In it, the values for orbicularis oculi (OO) and extensor digitorum communis (EDC) were obtained from2 0 subjects, 9 men and 11 women, using concentric EMG needle electrodes. None of these subjects were taking medicine or exhibited the symptoms of any medical conditions that could have interfered with the study.
A separate myasthenia gravis cohort of 56 individuals was examined between 1999 and 2003. These patients were selected because they had a positive AChR antibody tither as well as an MG diagnosis.
In the normal subjects, SF jitter was analyzed according to Stålberg’s method, the MCD values recorded were not different between the two muscles, and no potential pair with impulse blocking was recorded in these subjects.
In the MG patient subjects, a series of ROC, or receiver-operating characteristics, were constructed in order to evaluate the viability of concentric EMG needle electrodes for the purposes of detecting jitter and diagnosing MG.
Typically, the standard method for SFEMG uses a single-fiber EMG needle with a 25μm active recording core set in the side of the cannula. This test utilized concentric EMG needles with a .3mm diameter and a recording area of .03mm2. In order to suppress low frequencies and leave potentials with fast rise-time spike components, the testers adopted 2kHz low-frequency filtering.
This low frequency filtering setting reduced spike amplitudes, so the test administrators also adopted a lower amplitude criterion of 100μV. They also ensured that the spike potentials used for analysis were clearly separated from the baseline and had a fast rise time.
Potentials with two or more spike components were recorded and recordings were rejected if there were overlapping potentials, if fewer than 20 consecutive discharges were recorded, there was an interpotential rate greater than 4ms, or if the variation is discharge rate contributed to jitter, with an MCD/MSD ratio of greater than 1.25.
Ultimately, the sensitivity of the CNE tests was determined to be 96.4% and delivered no false positives, indicating that concentric EMG needles electrodes may be a suitable alternative to traditional single-fiber electrics.
(It should however be noted that there are instances in which SFEMG needles should still be used. For instance, only SFEMG needles can be used to detect fiber density [FD], and should be used in borderline cases.
Another study also corroborated the finding that concentric EMG needle electrodes can be used to record muscular jitter as an alternative to single-fiber electrodes, with two caveats: reference values obtained using CNE generally correspond to SF EMG electrodes, but are a few microseconds lower, and that borderline cases should be assessed with caution. Nonetheless, CNE show potential in cases in which traditional single-fiber needle electrodes cannot be used.
A Viable Alternative and Cost Savings, and Potentially Reduced Infection Risk
The potential for concentric EMG needles as a replacement for SF needle electrodes in SF EMG is welcome for two reasons: cost and safety.
The expense of SF EMG needles is well attested, with a single reusable needle costing many times more than disposable concentric EMG needles, at as much as $350 each. Concentric EMG needles are substantially more affordable, and in some cases, can cost as little as $170 for a box of 25 disposable needles. This drops the per-unit cost of these single-patient disposable alternatives to as low as $14, less than 5% of the cost of the traditional reusable alternative.
In addition to the potential cost savings of using disposable concentric EMG needles in place of single-fiber EMG electrodes, there is also concern about the risk of spreading prions, which disposable electrodes can help prevent. Given the difficulty of removing these infectious particles via conventional means, the use of single-use disposables is a much more secure failsafe.
LifeSync Neuro is proud to carry some of the industry’s highest-quality concentric EMG needles, in a variety of gauges and lengths, as well as EMG cables. Our high-quality, color-coded concentric EMG needles are pre-sterilized, with a stainless steel electrode core, as well as a silver-plated cannula and a gold-plated coaxial connector. They’re optimized to deliver high signal quality for accurate EMG recordings.
If you have any questions about disposable concentric EMG needle electrodes or their suitability for SFE EMG recordings, or would like to speak with one of our representatives about how to streamline fulfillment, please contact us at 1-800-358-2468.
Sources:
- Selvan VA. Single-fiber EMG: A review. Ann Indian Acad Neurol. 2011 Jan;14(1):64-7. doi: 10.4103/0972-2327.78058. PMID: 21654930; PMCID: PMC3108086. Retrieved 5/26/2023 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3108086/
- Sarrigiannis PG, Kennett RP, Read S, Farrugia ME. Single-fiber EMG with a concentric needle electrode: validation in myasthenia gravis. Muscle Nerve. 2006 Jan;33(1):61-5. doi: 10.1002/mus.20435. PMID: 16175626. Retrieved 5/26/2023 from https://pubmed.ncbi.nlm.nih.gov/16175626/
- Sanders DB, Kouyoumdjian JA, Stålberg EV. Single fiber electromyography and measuring jitter with concentric needle electrodes. Muscle Nerve. 2022 Aug;66(2):118-130. doi: 10.1002/mus.27573. Epub 2022 Jun 13. PMID: 35694863. Retrieved 5/26/2023 from https://pubmed.ncbi.nlm.nih.gov/35694863/
Stålberg EV, Sanders DB. Jitter recordings with concentric needle electrodes. Muscle Nerve. 2009 Sep;40(3):331-9. doi: 10.1002/mus.21424. PMID: 19705424. Retrieved 5/26/2023 from https://pubmed.ncbi.nlm.nih.gov/19705424/