Perineal and foot muscle synkinesis following trauma to the sacrum in an adult male - A case of motor root ephaptic transmission?

Ephaptic transmission has been proven as an alternative to chemical synaptic neural transmission and occurs in pathological situations, such as epilepsy and demyelination. Hereby, we report the case of an adult male that in 2012 was involved in a low-speed motorcycle accident with sacrum impact that from day three onwards reported unwanted penile movement when performing hallux and toe plantar flexion of the right foot. Urologic studies and perineal MRI were unremarkable but sacral MRI showed a significantly stenotic canal at the S1-S2 level while EMG displayed chronic moderate right S2 radiculopathy. Nine years later the patient underwent surgical decompression of the sacral canal with complete resolution of the synkinesis. We hypothesize ephaptic transmission between adjacent motor nerve fibres at the S2 sacral nerve root to be the likely mechanism explaining this phenomenon.