EMG Service, Local Health Unit 7, Siena, Italy.
Clin Neurophysiol. 2013 Feb;124(2):405-9. doi: 10.1016/j.clinph.2012.07.020. Epub 2012 Sep 18.
Normal sensory nerve action potential (SNAP) amplitude is a classical neurographic rule whether damage is located proximal to the dorsal root ganglion (DRG) as in radiculopathy. The study's aim is to check SNAP reduction in patients with lumbosacral radiculopathy due to herniated disc (HD).
A total of 108 consecutive patients with lumbosacral monoradiculopathy were prospectively enrolled. The diagnosis was based on clinical findings and magnetic resonance imaging (MRI). Electromyography of muscles of L4-S1 myotomes, motor neurography of peroneal and tibial nerves and sensory neurography of saphenous, superficial peroneal and sural nerves were performed. Percentage decrease in SNAP amplitude of nerves between healthy and affected sides was calculated.
Significant SNAP amplitude asymmetry was observed in superficial peroneal nerve in seven patients with L5 (12.1%) and in sural nerve in one patient with S1 (2.4%) radiculopathies. All these patients had foraminal HD.
SNAP amplitude reduction of sensory nerve originating from damaged root is present only in 7% of radiculopathies and is likely due to DRG compression when located proximal to the spinal foramen or within the intraspinal canal.
Preservation of SNAP amplitude in radiculopathy remains an electrophysiological dogma with a little exception. If the reduction of SNAP amplitude affects other nerves, causes other than radiculopathy should be sought.
正常感觉神经动作电位（SNAP）幅度是一种经典的神经图学规则，无论损伤位于背根神经节（DRG）近端，如根性病变。本研究的目的是检查因椎间盘突出症（HD）导致的腰骶神经根病患者的 SNAP 减少。
共前瞻性纳入 108 例腰骶单神经根病变患者。根据临床发现和磁共振成像（MRI）进行诊断。对 L4-S1 肌节的肌肉进行肌电图检查，对腓总神经和胫神经进行运动神经图检查，对隐神经、腓浅神经和腓肠神经进行感觉神经图检查。计算健康侧和患侧 SNAP 幅度的百分比降低。
在 7 例 L5（12.1%）和 1 例 S1（2.4%）神经根病患者中观察到腓浅神经存在明显的 SNAP 幅度不对称，所有这些患者均有椎间孔 HD。
仅在 7%的神经根病中观察到源自受损神经根的感觉神经 SNAP 幅度降低，这可能是由于 DRG 受压位于椎间孔近端或椎管内。
SNAP 幅度在神经根病中的保留仍然是一种电生理学教条，只有很少的例外。如果 SNAP 幅度的降低影响到其他神经，则应寻找其他原因，而非神经根病。
