S89 Neuromuscular junction assessment in children

Abstract

Disorders of the neuromuscular junction in children include the autoimmune conditions and congenital myasthenic syndromes (CMS). They are difficult to diagnose. The neurophysiological tests available are repetitive nerve stimulation (RNS), which is not as sensitive as the single fibre EMG (SFEMG) techniques. Stimulation SFEMG (StimSFEMG) is the preferred technique in children. StimSFEMG rarely allows single fibres to be identified particularly when using a concentric needle electrodes (CNE). For this reason the technique is described as Stimulated Potential Analysis using Concentric needle Electrodes (SPACE). It is performed on orbicularis oculi. A monopolar needle is placed near the facial nerve as it passes over the zygomatic arch. A CNE is placed in the orbicularis oculi at the outer canthus. Stimulation at less than 1 mA is used to evoke responses from the orbicularis oculi. Stimulation frequency is increased to 10 Hz and minimum of 20 repetitions were recorded. The automatic peak detection algorithm is used for the identification of potentials and calculation of the MCD. At least 10 potentials are collected. The results are presented as the MCD- I % (MCD/upper limit of normal for age). SPACE had 84% sensitivity and 74% specificity for the primary NMJ disorders. Receiver operating characteristics (ROC) curve identified an MCD-I >115% as providing best diagnostic accuracy with sensitivity of 77% and specificity of 84%. SPACE is practicable and safe in unsedated children. It can be used as an effective screening technique for neuromuscular junction abnormalities in children.