Introduction: Complex repetitive discharges (CRDs) are thought to result from depolarization of a single denervated muscle fiber, followed by ephaptic spread to adjacent fibers. This leads to cyclic spread of the depolarization to produce a recurrent discharge. Another explanation is suggested.
Methods: CRDs were recorded with single and multiple electromyographic needles longitudinal to muscle fibers in 39 neuropathy patients.
Results: The mean frequency of CRDs was 26 Hz, mean number of negative spikes was 5.4, and blocking of spikes occurred in 53% of CRDs. In multi-needle recordings most CRDs were local, but propagation of the discharge was sometimes observed.
Conclusions: The prevailing hypothesis of CRDs cannot explain local CRDs. Type II afferents of bag2 and chain fibers branch widely in the juxtaequatorial region of muscle spindles where they may intermingle with motor terminals. Ephaptic transmission from type II afferents to static γ and β efferents may cause CRDs and fix the CRD frequency.
Keywords: complex repetitive discharge; electromyography; fusimotor; muscle spindle; type II afferent.
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