END-PLATE SPIKE MORPHOLOGY - A CLINICAL AND SIMULATION STUDY

Objective: To describe the various morphologic appearances of endplate spikes, define the theoretical volume conduction basis of these wavef orms' morphologies, and simulate ''atypical'' endplate spike waveforms documented by other investigators. Design: Endplate spikes were recor ded from the biceps brachii in healthy individuals using a monopolar n eedle electrode. The morphologies of these waveforms were compared wit h those obtained from a computer simulation. Previously documented end plate waveforms were simulated using two fundamental types of biphasic initially negative and positive waveform morphologies. Setting: Unive rsity clinic outpatient electrodiagnostic medicine facility. Subjects: Five subjects without history or physical evidence of neuromuscular d isease. Main Outcome Measures: Endplate potential morphologies were as sessed with respect to overall waveform shape and number of phases. Co mputer-generated waveforms for individual endplate spike waveforms wer e qualitatively compared with those recorded from the subjects. Result s: Three fundamental waveforms were documented to arise from the endpl ate regions of all subjects and were successfully simulated: (1) bipha sic initially negative potential from the endplate itself and up to 0. 2mm from the endplate, (2) triphasic initially positive potential from within 0.2mm of the endplate up to 0.5mm from the musculotendinous ju nction, and (3) biphasic initially positive potential from the last 0. 4mm of the fiber or from impulse blocking. Two biphasic endplate spike waveforms could be summated to generate all other endplate waveforms described in previously documented literature. Conclusion: The combina tion of clinical and simulation studies suggests that endplate spike p otentials can have quite varied morphologies. Triphasic initially posi tive and biphasic initially positive endplate spikes may be mistaken f or fibrillation potentials and positive sharp waves, respectively. The triphasic waveforms most likely arise from an action potential propag ating past the recording electrode adjacent to the endplate, while the biphasic initially positive potential is simulated to arise from the needle electrode blocking action potential propagation. (C) 1998 by th e American Congress of Rehabilitation Medicine and the American Academ y of Physical Medicine and Rehabilitation.