Concentric or monopolar electrode for jitter determination in orbicularis oculi

Abstract

ObjectivesTo investigate if monopolar (MN) and concentric (CN) electrodes are equivalent for volitional contraction jitter estimation in orbicularis oculi (OO), and to study the effect of selecting a specific high-pass filter. MethodsWe studied neuromuscular jitter in OO on both sides in 100 consecutive patients with a clinical diagnosis of ocular myasthenia gravis (MG). We used either MN (50 patients) or CN (50 patients) electrodes in individual patients, according to a randomised protocol, with a 1kH high pass filter on one side and a 3kH filter on the other. Ten or more potential pairs were studied on each side. Results48 patients had a definite clinical diagnosis of ocular MG, and 52 of mimicking-disorders, who were analysed as controls. In controls, jitter (MCD) showed a normal distribution independent of the electrode type or filter settings. The mean jitter value and the number of abnormal pairs (>10%) was similar in MN and CN recordings, with both 1 kHz and 3 kHz filters. Sensitivity was 73% for mean jitter and 94% for number of abnormal pairs. Specificity was 100%. ConclusionsThe jitter in OO using MN or CN was similar in controls and the diagnostic sensitivity was similar using either electrode in patients with ocular MG. The use of high-pass filters of 1 or 3 kHz did not influence these results. SignificanceMN and CN are both suitable for determining volitional jitter in OO.