Neurophysiologic assessment of nerve impairment in posterolateral and muscle-sparing thoracotomy

Objective: This study was aimed at analyzing the degree of intercostal nerve impairment in posterolateral and muscle sparing thoracotomy and at correlating the nerve damage to the severity of long-lasting postthoracotomy pain. Methods: Neurophysiologic recordings were performed 1 month after either posterolateral or muscle-sparing thoracotomy to assess the presence of the superficial abdominal reflexes (mediated in part by the intercostal nerves), the somatosensory-evoked responses after electrical stimulation of the surgical scar, and the electrical thresholds for tactile and pain sensations of the surgical incision. Results: The patients who underwent a posterolateral thoracotomy showed a higher degree of intercostal nerve impairment than the muscle-sparing thoracotomy patients as revealed by the disappearance of the abdominal reflexes, a larger reduction in amplitude of the somatosensory-evoked potentials, and a larger increase of the sensory thresholds to electrical stimulation for both tactile perception and pain. In addition, these neurophysiologic parameters were highly correlated to the postthoracotomy pain experienced by the patients 1 month after surgery, indicating a causal role for nerve impairment in the long-lasting postoperative pain. Conclusions: This study shows for the first time the pathophysiologic differences between posterolateral and muscle-sparing thoracotomy and suggests that the minor long-lasting postthoracotomy pain in muscle-sparing thoracotomy patients is partly due to a minor nerve damage. In addition, because nerve impairment is responsible for the long-lasting neuropathic component of postoperative pain, it is necessary to match specific treatments to the neuropathic pain-generating mechanisms.