Seyam S. Salem¹, Amira M. El-Gohary¹, Nevin M. Shalaby², Al-Shaimaa S. Khalil¹

Departments of Clinical Neurophysiology Unit¹, Neurology², Cairo University; Egypt

Background: Peripheral deafferentation is known to induce neuroplastic changes in the neuronal system, but there is paucity in studies addressing pain influence on neuroplasticity. Objective: To assess the relationship between chronic pain and plasticity in somatosensory pathway. Methods: A cross sectional study including 20 Egyptian patients with unilateral cervical radicular pain. Patients were neurologically assessed and pain severity was graded. Magnetic resonance imaging of the cervical spine, and electromyography, for evidence of deafferentation, were performed. Somatosensory evoked potential studies after digital nerve stimulation of thumb, little finger on painful and non painful sides were done. Somatosensory evoked potential parameters were compared within individual patients and with those of 10 age and sex matched control subjects. Results: Pain severity was graded as II in 13 patients and III in 7. The 6^th cervical root was the most involved root clinically and radiologically. There was no evidence of deafferentation in 75% of patients. Amplitudes of EP, N13, N20 and P22 after stimulation of the painful thumb were greater than those of the non-painful thumb, little finger on painful and non painful sides within patients group and those of controls. The amplitude difference of EP showed the least change relative to other waves among patients. The amplitudes correlated with pain severity and duration. Conclusion: Pain can induce neuroplastic changes within the somatosensory pathway, irrespective of presence of deafferentation, involving both peripheral and central levels but more evident centrally. Such changes are selective to the involved territory. [Egypt J Neurol Psychiat Neurosurg.  2012; 49(1): 59-66]

Key Words: cervical radicular pain, neuroplasticity, somatosensory evoked potential.